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Hey brother, I think I have you covered. I have a '62 M20C with bladders and I just did a custom Fuel Stik for my plane. I used a siphon plus a 2 gallon gas can and measured out two gallon increments to get accurate numbers. I don't have an engine monitor but have tested the burn based on power settings over 10 flights since measuring and the numbers come out within about a half gallon or so of where I predicted. If you'd like to buy a stick from Fuelstik.com, Sportys, Aircraft Spruce, etc., then you should be able to use this scale. By the way, I cleared up a bit of a mystery when I was working on this project about the true fuel volume of the bladders. My '62C when built had only 48 gallon tanks according to the owners manual. My aircraft and STC records only reference bladders added and their serials without stating the fuel capacity, so I reached out to Griggs who confirmed that my tanks were indeed expanded to 54.8 gallons total with the bladders because that bladder 27.4 gallon bladder (each) size corresponds with their part number. So now I know for certain that my tank capacity is indeed higher thanks to the bladder STC. I cannot recommend Griggs enough based on the level of help they provided in pursuit of answering my burning question. I will not hesitate to work with them if needed in the future. Printable Mooney M20C 27.4 Gal N6475U 6-16-23.pdf

Every new 2U aircraft gets to go through the same challenge…. Check the Calibration of the fuel instruments…. Check the actual useful volume of the tanks… Know their limitations… Some tanks can get filled beyond what their instruments can measure…. Some Monroy installations add extra volume, but may not have a method of measuring that extra volume… and the tanks don’t empty in series… (this could be why the EVP is only measuring the original fuel volume, and not including the extended tanks…) Some digital displays are really good… Some digital fuel floats are really good… Some fuel flow meters and fuel totalizers are really nice… If you have fuel gauges on the wing… know they are calibrated while the plane is on the ground… The fuel gauges on the instrument panel are calibrated while the plane is level in flight… (on the ground requires using a level on the sheet metal seam on tail cone….) If you have to rely on 1 gal accuracy… it can be done. Start with an empty tank… with the last drops emptied by the engine or through the fuel separator… fill it one or two gallons at a time… (park next to the fuel pump) If you have Ceis fuel gauges… there is a procedure for that… If you are building your own fuel stick… this works as well… Know how many fuel floats you actually have… some big tanks get two each… It is important to have the most accuracy as the tanks reach zero… but it is also really important to have them be accurate at half full too… How you fill the tanks can also affect the details… start on a nice level pad… PP thoughts only, not a mechanic… Best regards, -a-

I wonder how many MSers are like me about fuel measuring? I like to know that my dip stick and my gauges are accurate down to the gallon. However this is an academic exercise for me. If I am flight planning and get down to anything approaching 10 or 12 gallons, I am going to plan something different. If I am flying, it is even worse. I have had my plane for 22+ years, and have seen only one low fuel light on one tank come on. That, or course, doesn't count when I ran a tank dry intentionally, to make my fuel stick. Except for my crazy desire to know it is precise, I doubt if it would ever make a difference if all my measuring devices were off 10 gallons.

In theory, you are absolutely correct. In practice, there are a couple of problems. I think there are some variations in the capacities of tanks due to minor variations in the production. Also it is very hard to establish where "full" is, both when you are looking at published useable fuel and when you are measuring your own. The extrapolation is also a little tough to be super accurate. It is not as liner as we would like. But this is not much of a problem at the lower fuel levels, as it takes a few gallons before it begins to show on the stick But overall, this method will get you awfully close. We all like to know, down to the ounce, exactly how much fuel is there, but in practice, nobody (with good sense) ever flies that close to the limits. I still think the best way is to fly one tank down to where the engine sputters. (And no, there is no real danger here. It is only a little spooky the first time you feel that loss of power. Remember, the early POHs approved the process) Land and add fuel in one or two gallon increments, marking your stick as you go. I also suspect to be super-duper accurate, you would have to have a separate stick for each side.

I made a lookup table with the height of fuel level in both tanks and corresponding quantity by completely emptying them and adding 4gl at a time and measuring the levels. So I measure the amount with a stick before flying. During flight, I go by jpi totalizer. I take the level gauges seriously only once they've dropped below 16gl on each side: that pretty much corresponds to fuel level right at the connection bulkhead nipple... YMMV.

Hi, I'm a new member and new owner of a 1975 M20F. I love the plane and am just getting use to it after my complex checkout. Does anyone know of where I can get a "Dip stick" for directly measuring the amount of fuel in each tank of an M20F? If someone has one, maybe I could just get the measurements and make it with a thin piece of PVC or wood. Thanks, Larry

Ok I know it has been discussed, but I can't find exactly what I am looking for - Mine is the M20F Model with 32GAL tanks on each side (no bladder). Anyone have a measurement stick they could show me next to a measuring tape so I can make my own? And yes, when the money is there I will be going the Cies route. Probably in 2019.

Hi guys! Is there a ready-made fuel stick for a J? Thanks!

There was a quite a bit of discussion about running a tank dry on mooneyspace a few years back, several people said they do it frequently. It is a little different issue in a turbo (like mine) than an NA because the turbocharger will spool down even if the prop keeps windmilling. The engine becomes an NA but with turbo compression ratio. Special procedures in the manual about airstarts above 12,500. Less of a deal with an NA I would think, because first of all you are not likely to be at an altitude where the engine can't run without compressed induction air. The classic method is to start at full MP full rich and lean out until the engine starts. I did it once after all that previous discussion. What I can tell you is that the time from the first stumble to the hand reaching the switch and switching tanks can be measured in microseconds. Restart was a non issue. As long as the prop is windmilling and you have a reasonable amount of altitude it works out ok. I fly so much under IFR flight plans that I am really not willing to do it again. Don't want to discover that the restart takes longer than expected and have to report to ATC that the engine stopped and you are restarting so will lose altitude. Maybe do it VFR. CoffeeCan mentioned the fuel management method I have written about in the past. To add to that method, if I am going to fly a mission where I need to carry, let's say, 15 gallons less because of weight and balance, I will contrive to fly a prior flight where I can use the fuel flow meter to draw down at least 15 gallons from one tank. Then when the mission comes up, I fill the other tank completely full. Now I have one full tank and another tank that I know from fuel meter readings is down 15 gallons, and I have made weight and balance. Then I would use the partially full tank for takeoff and climb, leaving some fuel in that tank. At cruise, I switch to the completely full tank, and now have about 2 1/2 hours in that tank to get where I want to go (or three hours if I am LOP), plus some extra fuel in the tank that started partially full just in case I need it for descent and landing. My Mooney flies just fine with the tanks complete "unbalanced," there is no good reason to switch back and forth every hour or whatever. It just makes the fuel calculation confusing, and you don't want confusing. Obviously, if during the prior flight you drew one tank down, say 25 gallons, and you want it at 15, then the easy thing to do is to put 10 gallons in that tank (so you are now short just 15 gallons), and fill the opposite tank completely full. This let's you use the fuel flow meter, which I have found in my plane to be very accurate. If you don't have the antisiphon valve you can also make or buy a measuring stick and actually measure what is in the tanks.

The inboard sender is to the cabin side looking down the filler from the front of the wing. Without blowing yourself up, use your fuel measuring stick to see where it is. A flashlight should also be useful for looking around down the fuel filler. be very careful with seating the caps. If they are adjusted properly (you replaced the o rings right) It should be a slight snapping action to get them down. Line guys will pound them down and break the ears off.

I was shopping for a fuel measuring-stick for my recently acquired '65 C model but realized that there is a point where the fuel is actually much out of sight and I can see the bottom of the tank (bladders installed). IIRC my the fuel gauge read 1/4 (not positive about that). Am I missing something here? I've always flown Cessna aircraft so I've never run into this before. It left me wondering how useful a dipstick would be. Is this a low-wing thing, or a Mooney thing? Or am I nuts?

Want to see how other MSers have gone about measuring? https://mooneyspace.com/search/?q=Fuel measuring stick&sortby=relevancy&search_and_or=and Best regards, -a-

Yes, a fuel measuring stick is very useful for your M20C. The best fuel stick will be one you make yourself. A wooden dowel, a paint stirrer, or similar that you mark yourself will be the most useful. The max fuel you can have in the tank without reaching it with a fuel stick, is only about 8 gal. And that is probably not enough to consider for take-off purposes. In other words, if there's not enough fuel in the tank to measure with your stick, there's not enough fuel to go fly. From here it gets more high tech, more accurate, and more expensive. Get an engine monitor with proper fuel flow and (primary) digital fuel gauges. Pair that with CiES digital fuel senders. Now you'll know how much AND where it is at all times. Typically accurate to within 1/2 gallon on each side. The more accurate your fuel information, the more range you have, the safer you are, and the more peace of mind you enjoy.

DISCLAIMER: The fuel measuring stick I shared on this forum is only intended for situational awareness on the ground and shouldn't be used as conclusive evidence for how much fuel is in each tank of a 1967 M20F in its OEM configuration. In other words, do not trust or rely on the fuel measurement stick what-so-ever! The markings on it carry no meaning and the stick should only be used for stirring paint.

YES! Thank you!!!!! I have an M20F which has 32Gal tanks on each side. This is EXACTLY What I was looking for in this thread. A measuring tape right next to a Gallon representation of what is actually in the tank and explanation of where to rest the wooden stick to measure. THANK YOU THANK YOU THANK YOU! Now since it is "my" thread I'll make a couple of soap-box comments: 1) Thank you all for posting, I love that I can come here with mooney specific questions and get a ton of advice. 2) I don't think the Fuelstik option will work for me because it only has the 27Gal per tank printable scale. :( 3) CIES is doing a great thing and makes a lot of sense! I mean, when I tell non-pilot people that I use a stick to measure a wet tank of fuel on my plane they think I am a caveman. When was the last time you saw anyone using a stick to measure a tank in their car at the gas station? exactly. Now do I want to pay the price of a used car to get that rocket-science technology? Its on the short list...but I'm hoping the cost will come down some how. (I know I know - low volume production in the aviation industry combined with FAA and insurance hurdles in a sue-happy society doesn't seem to allow for low-cost aviation products so we'll just hope for some change later down the line). 4) Why do people feel the need to be rude in this forum toward anyone? I mean, if CIES wants to put a plug in for a product that works for the aviation industry/mooney pilots whats wrong with that? If you don't like the post then don't get butt-hurt, just move on, don't whine, keep it to yourself and keep the conversation clean. We can all agree to disagree politely if need be. 5) For now, I will be measuring with this stick from Browncbr1, then adding fuel to accomodate my flight plus 1.5hrs - setting a personal minimum, if I need more fuel then I schedule a stop in my trip, that works since I have long legs and need to stretch anyway! In the future, I am hoping CIES or someone will be creating an accurate fuel sending system to replace my current system (which I don't trust) at a more manageable price than what is currently advertised. I am new to this industry but I am a control systems engineer so maybe I'll come up with one even. :)

I definitely see value in the CiES fuel measuring system. Anytime your fuel consumption is different in-flight than what you originally planned, you have no idea how much fuel you have with the old stick method. Our local priest, with over 50 years of safe flying experience, just ran out of gas and landed in a bean field last Thursday at the end of a long cross country. He sticked his tanks and calculated that he had 45 minutes reserve in an Archer. When flying, he flew lower than planned and was burning fuel faster than he thought. Had he had accurate gauges in-flight, he may not have landed 1/2 mile short of the airport. What I don't see any value in is a $10 plastic tube instead of a free wooden stick. Both give you the exact same information with the same accuracy. Likely more accuracy with the wooden stick if you calibrate it yourself vs buying a pre-calibrated plastic tube or using someone else's measurements.

You're implying an indication issue on your left tank. If so, you need an independent method of measuring tank volume from both fuel caps to verify. But you haven't given an estimate on the amount of missing fuel over the course of the couple weeks you mention. For example, is it large enough to be noticeably different visually looking into both the main and extended tanks? Or are we discussing more like small number of gallons that you won't be able to tell the difference visually but still plenty to be more than a seep? First, there is no secret place fuel can drain too. Any leak is going to be very obvious, fuel is going to seep or drip directly out from a leak, or if inside the wing, such as up higher, it will run downhill towards the center of the aircraft inside the wing till it finds a place to drip out which could be anywhere downstream including inside the cabin. It will be very evident and leave a unmistakable blue stain where ever it flowed, dripped or seeped from. Its certainly not always obvious exactly where a leak originates from since it can flow down the side of a tank and in the wing for quite a ways before it comes out but it will become visible externally on the aircraft or in the cabin soaking the carpet if its a significant leak i.e. more than a seep. With no evidence of a leakage, it suggest an issue with one of your senders - there are two in each tank wired in series. The wing gauge is not an independent gauge but magnetically senses the arm of the fuel sender below it - so it would make sense for them both to be off. Which brings us back to the point of an alternative method of measuring fuel volume in your left tank. I suggest you stick your Left main and extended tanks. Recording height of fuel level is adequate since you just need to know if the volume is really changing while the aircraft is sitting in the hangar. If there is no leak, its got to be an indication issue if someone isn't borrowing fuel from your tank. But so far, this doesn't sound related to having extended tanks since you are familiar with the how the tank gauges indicate differently as the fuel added to the main tank settles out into the extended tanks (since the extended tanks are a mere extension of the main tanks uphill and outboard of the main tanks in front of your speed brakes).

Think of all of the disclaimers that all of our present and future attorneys might scream... A week or so ago, I filled my right main tank 5 gallons at a time while marking on a dip stick. Attached is a photo of that stick along side a measuring tape. Of interest to me (that I now think I should have anticipated) the last three gallons of fuel are about the same dimension as the middle five gallons. It appears that the tanks are pretty linear (dip length-wise) until nearly topped. Don't use this for your aircraft, just a discussion point. Sent from my iPad using Tapatalk

Full is at the base of the pipe or fill tube. Above the base of the fill tube is for expansion. But yes you can keep filling above "Full" but you should be at rated capacity at the base. You should empty each tank and actually measure it as many Mooney owners have done since many have found they have less than than rated capacity. One reason for this is if sealant was applied to vent holes in the top of the rib, then the inside bay will not be able to vent the air and won't fill on its own. Before you count on gallons you may or may not have its a good idea to measure your capacity and calibrate your own dip stick for measuring partially filled tanks. It will also ensure you have an accurate weight for any fill level you decide to use. if you have the little fuel gauges on the top of the tank you can also verify their accuracy. They are usually pretty good.

Welcome aboard Harry. There are a couple of things to consider. 1) there are some locking mechanisms You might be able to find. Realistically, a thief with a wrench can disconnect the fuel sample valve under the wing and catch the fuel with less effort. No sucking on a tube required. 2) there are improved fuel level sensors from CIES that have accuracy of a gallon when read on a digital display like a JPI or other... CIES has posted some pictures of the new floats and arms they are building for Mooneys. 3) A calibrated Stick. In case you have spent all your free cash on the fuel. Many of us have built a variety of sticks to perform this task. There is always a difference between riding fuel level on the ground to in flight. The 8° nose up attitude on the ground is the reason for the difference. Of course, you will be measuring on the ground before you leave and after when you come back. These are the things that come to the mind of a PP. I'm not a mechanic, but I kinda know the CIES guy. He's been here a while. How does that sound? Best regards, -a-

Well several things that could be clarified 1) This is the hardest point - while the CiES fuel sensors are float based - they are definitely not analog. We use a non contact sensor system from the automotive industry, that for the last 10 years, has replaced error and wear potentiometers for throttle & throttle position by wire, brake by wire, steer by wire and stability control. This sensor technology is the major reason you don't have ABS pedal feedback in cars anymore. 2) Yes 3 points define a plane and with the appropriate technology a maneuvering fuel level can be detected - we have done this on a marine application. The FAA is different 3) Why pair an advanced sender with an analog gauge - not ideal 4) We are the OEM choice for new fuel quantity systems as a fuel quantity system is required for new aircraft and it should be within 3% in the range of zero fuel to full. OEM is really our market, so the response here is not a sales call to arms, as we are replacing potentiometer systems on all new manufacture GA aircraft, both Jet A turbo aircraft and avgas piston. If there is interest we would love to help out. 5) The FAA does not confer that a fuel totalizer a required instrument and as such there are far lower thresholds for operational performance, however they seem to provide comfort to the pilots that have them. . NOTE: We regularly (every week) show pilots the errors associated with totalizer systems on new aircraft. Knowns: - Fuel quantity is affected by ramp angles, gear set and fueling procedure (how the tanks are filled - one side then the other) - All transportation fuel tanks have expansion volume - In cars it is known as the "FULL tank reserve" Planes are unique in that in most models you can observe full fuel. - Dip Stick angle makes a large difference in fuel quantity - A gallon of water poured onto a level concrete slab will flow out to the average size aircraft fuel tank (strangely conveinant for illustration purposes) - this is the slight difference pilots swear they are measuring accurately and repeatedly. The above knowns makes statements regarding refilling consistently within a gallon very hard to fathom given the realities of the physics involved - I believe I have referred to it as a self fuel filling prophesy. 6) Be very careful calling a fuel totalizer a fuel gauge - While for some they are replaceable terms in the eyes of the FAA they aren't (well some in the FSDO are confused) 7) The FAA by its design regulations and guidance intended you to be able to stick the aircraft fuel tank in flight (the reality is strikingly different). That is what a proper aircraft fuel gauge should do, and no I am not joking.

The thing most of us seem to do is start with an empty fuel tank and a paint stirring stick or something similar. Add a known quantity of fuel (say 4 gallons or so), stick the stirrer in and mark where the liquid line is. Continue adding fuel in the amount you would like to measure (another 1, 2 or 4 gallons) and repeat the process until full. Measure as often as you like at the granularity you want. That should give you a measuring device that goes from empty to full. For me, the minimum is 6 gals on the stick. Less than that and I want to load fuel regardless of the length of the planned trip. A very unscientific device, but better than my eyes making a guess. YMMV. John

As I pointed out "I know there are many who would disagree" and I would love to have an accurate fuel measuring display but at this time I do not so I do what works best for me. Checking my caps is part of my CIGAR as they are easily seen from cockpit and I have calculated my fuel burn to be within a couple of tenths of a gallon on an over 3 hour leg (repeated many times). your comment about leaks or other factors only supports my approach even more. if I know that I still have an hours fuel in tank 1 and there ends up being a problem with tank 2 that causes a loss of power...well... I still have an hour to get down safely if tank 1 is dry end of flight. I just cant see the fault in this reasoning but it is good to have these discussions because I always learn from them. I have also determined what each of my gauges in the old Garwin Cluster is showing but I don't trust it to be accurate so I use the stick the burn and the time and never push my legs.

Not really directly related to this post and not wanting to hijack it, but I have a problem with my right fuel sender, I have a M20K Rocket with a serial lower than 25-0446, and when both tanks are full to the wing overspill level, my panel gauges are at Full on the left tank, but at 27 Gallon (3 rd making on the gauge ) on the right tank. I know that it must be the sender or the gauge the problem and looking to get it fixed at the next annual. So that being said, I'm also very interested in a measuring stick, what I find difficult is that with the claps at the tank opening, it is almost impossible to see visually how much fuel is in the tank unless it is full...

I am responding to Aaron's post (actually two of them), responding to my post about long descents and why the fuel remaining number is not very useful, and first, Aaron is correct, if you don't have a long descent to do, then my point about the reduced fuel flow during a long descent is not important. However, there are a couple of other reasons why the fuel remaining number that the 930 displays is not particularly useful to me, and maybe it would be helpful to explain what I do and why I do it. The 930, and for that matter all the JPI's that I am aware of that display fuel calculations, do not use actual measured fuel on board to display fuel remaining. My 930 has fuel gauges that display, with variable accuracy, how much is in the tanks. But the fuel remaining is calculated based on measured fuel flow subtracted from an assumed number. My aircraft, for example, has a usable fuel capacity of 75.6 gals. usable. At the beginning of every flight the 930 asks if I have refueled, and if I say yes it resets to fuel to 75.6 gals. It has no idea how much fuel I have actually put in the aircraft. There is a function for reducing or even increasing that number, if for example I know I only have 50 gals. on board I can use one of the buttons to reduce the starting number. It is quite a lot of screwing around to do that if the number is much different from 75.6 . But the bigger issue is that whatever number it starts with, is not an accurate measured number, it is either 75.6 or the number I tell the JPI to use. That puts a premium on making sure the tanks are actually full to the top when I am going to fly a trip where full capacity is important. On those occasions, I either fill the tanks myself or supervise, and it is necessary to rock the wings to get all the trapped air out. On shorter flights where fuel is not going to be critical I don't bother with that, I know that even if I am 5 gals. short in each tank, I am going to have lots of fuel left over at the end of the trip, that is one reason why the JPI's reported number is not very useful to me. My aircraft has anti-siphon valves, which are just flappers that come from inside the tank and cover the filling hole. They are there so that if the seal on the fuel cap fails, the fuel won't get sucked out of the tank. That is nice, but they make it impossible to stick a measuring tube or stick in the tank, so in my case I can't really measure how much is there if the tanks are only partly full, most of the time I just fill them to the rim and that is 75.6 gals. The other and probably more important reason that the JPI's fuel remaining number is not very useful, is that the JPI does not have a way of knowing how much is taken from each tank. It starts with the number that is given, usually 75.6 gals., and then subtracts measured fuel flow. So it provides a total fuel remaining, but can tell you nothing about where the fuel is. So even if it calculates that I have 37.8 gals. left, which is about three hours of fuel, it cannot tell me which tank it is in. Gauges, at least in my aircraft, are mediocre for this task because regardless of how new and up to date the readout is (i.e. a 930 instead of the factory strip gauge), most of us still have the factory senders in our tanks, they are old and not very accurate in most cases. They have a habit of sticking in spots, and then freeing up, so you may fly for two hours with the display showing 37.8 gals. in the tank, and then suddenly there are only 10 gals. In my aircraft the gauges show zero fuel when I have somewhere between 6 and 8 gals. left in the tank, and that is a total of around one hour's worth of fuel that the gauges are not going to tell me is there. What I have done is to test out the fuel flow meter. I did this by following the instructions in the JPI manual, filling the tank to full capacity (filling it myself), flying three flights of about 2 hours each, refilling to the same place each time (to the brim) and noting the fuel used, then comparing the fuel used from the gas pumps over those flights, to the number the JPI gave me. It was accurate to a tenth of a gallon over 50 gallons, and I did this twice just to be sure. So I have confidence that the one reading in my aircraft that will be accurate is fuel flow (which reads as "USD" on the JPI). The one piece of paper I use in the cockpit is a blank sheet on which I write a chart, starting with 37.8 in each tank and then subtracting what I have used from that tank each time I switch. I will typically ascend to cruise and then cruise for awhile on one tank, then switch when I have reached a "USD" number that is around 20 gal., and just for luck I like it to end with a .8. So lets say I switch at 18.8 USD. My chart shows me that I now have 19 gals. in that tank (I usually start with the left tank). I have now been in the air somewhere around an hour to an hour and a half. When I make the switch, I will cruise on the new tank until it is time to start the descent (which from the flight levels is usually quite a ways out). At that point I will switch over, knowing that I have about an hour and a half on the descent tank, which is about twice what I need. Better yet, I am dead certain it is 19 gals. in that tank, I am not guessing where it is and how much there might be in that tank. The number that the JPI reads out for "fuel remaining" is a total fuel number. When it tells me I have three hours remaining, I know that the fuel flow it has subtracted is very accurate, but I also know that the starting number was an assumption, not a measurement, so the ending number is based on an assumption. What the fuel remaining number cannot tell me, is where that three hours of fuel is. Nothing the JPI has on it, whether hooked to a GPS or not, is going to be able to tell me that with any degree of accuracy. The gauges are just a "best guess." When I installed the JPI I looked at ways to get a better measured fuel number. EI has a different type of fuel sensor that is supposed to be much more accurate than the old style float sensors. EI's rep. was on this site for awhile and I asked whether the EI senders would work with the JPI. He could not tell me and said that was a judgment my A&P would have to make. The installation of all new sensors was also a very pricey thing, there are two sensors on each side, so I stuck with the factory senders. The EI engine monitor, obviously, would work with the EI sensors. But when I was looking at the MVP-50 a few years ago, its fuel remaining calculation was done in the same way as the JPI calculation, that is, it was based on an assumed starting number and not on measured fuel in the tank. So the bottom line is that I don't find myself using the fuel remaining number that the 930 displays very much at all. It is a secondary verification for the actual, accurate, fuel flow numbers I have on my little paper chart. And by the way, that chart is a scrap, sometimes I write it on the back of a fuel invoice folded up. I just want it to be permanent and not subject to change under any circumstances. I am not saying it is not fun to have that "fuel remaining" number, just that, when I need something I can count on, like exactly how much fuel is in which tank at the end of a long cross country of several hours, that "total fuel" number is not very useful.