Fuel Guages reading incorrect

[The201pilot]

So, after solving the high CHT temp (Baffling problem) we're on to my next small squawk..The fuel tank guages don't read correctly.  Not that I rely on these solely, just a mental thing really. (Usually tanker around full tanks) in addition, all of my flights so far have been between 2.5-3hrs.  LWJ has bladders so the wing guages are out of the question.  I guess i need to have the tanks opened up ? Or is there another way we can go here ? Any other similar experiences out there ?

 

Thanx..

[FBCK]

Screamingtrees, I'm in Calgary as well and would be interested to hear who has been servicing your Mooney, you can PM me if your more comforable doing so.  I have a leak in my left Monroy tank and will be taking down to the US in the spring.

[jlunseth]

Not entirely sure what your question is, but you seem to be asking what it might take to get your fuel gauges to read accurately.  You are not alone in this by the way, I will hazard that virtually any Mooney or other aircraft out there that is over 20 years old (and lots of younger one's too), have the same problem.  The older style wing tank sensors are not great and never were.  If you are looking for your gauge to read 5/8ths full when the tanks are 5/8ths full that is probably not going to happen even if you replace the sensors with new factory sensors.

There are much more accurate, electronic probes available. Electronics International sells a capacitative probe: http://www.buy-ei.com/Pages/FL-1/FL-1_Probes.html .  Probably there are others.  You need to make sure, however, that the probe is compatible with the gauge.  I tried to find out if the EI probes are compatible with my JPI 930 (can the 930 read the signal from the EI probe) and basically got the answer that it is up to the installing A&P to figure it out. 

I don't completely ignore the fuel gauges, but have learned that using the results from the fuel flow gauge is much more accurate.  I have tested out my fuel flow gauge by filling the tanks before a flight, then finding out how much needs to go in after the flight to refill each tank.  It is best if you do the filling of the tanks yourself, so you are filling them the same way each time.  Then total up three flight of two - three hours in length and compare the total of what you have put into the tanks, to what the fuel flow meter says you have used.  In my aircraft, the fuel flow meter is accurate to the tenth of a gallon out of 50 gallons, in other words, if the measured usage was 50 gallons the fuel flow meter will say I used 50.1 .  That is close enough for me.

To use this for flight monitoring, I make sure the tanks are full at the beginning of the flight (37.8 gal. per tank in my aircraft) and then subtract what the fuel flow gauge says has been used each time I switch tanks.  I set up a little table on my kneeboard to track it.

Using this method, I have discovered that when a tank gauge reads empty, I actually have somewhere around 6-10 gals. left in the tank (the left tank gauge seems to be more accurate than the right).  That is, lets say, 16 gallons out of the 75.6 that can't be accurately measured by the fuel gauges, which is more than an hour's worth of fuel.  On a long trip, having that fuel measurable and available makes a big difference.  

You can also make a fuel stick to measure what is actually in the tank before you depart.  That does not work in my case, because there is a flap in the fuel inlet that closes, so I cannot actually see into the tank or put in a stick.  Maybe yours is different. 

Hope that helps. 

By the way, I am told that if you want to replace the factory sensors with new, there are actually two sensors in each tank, so you would be replacing four sensors.

[KSMooniac]

I'd be more surprised if they read correctly.    You can chase this problem thru the sending units and electrical connections, but I wouldn't fret too much and put the money towards a fuel totalizer system if you don't already have one.  As jlunseth pointed out, they are far more accurate and remove ALL anxiety about fuel levels on long range flights.  They also allow you to confidently fly around without topping-off every flight, which gives you better takeoff, climb and cruise performance.

[Parker_Woodruff]

Quote: KSMooniac

I'd be more surprised if they read correctly.    You can chase this problem thru the sending units and electrical connections, but I wouldn't fret too much and put the money towards a fuel totalizer system if you don't already have one.  As jlunseth pointed out, they are far more accurate and remove ALL anxiety about fuel levels on long range flights.  They also allow you to confidently fly around without topping-off every flight, which gives you better takeoff, climb and cruise performance.

[fantom]

Quote: Parker_Woodruff

 +1.