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That's a really good analysis of what I should expect for oil temeperature! Good to know. By any chance would you have any idea at what temperature should I expect the vernatherm to open up? 200? I do have a Reiff XP system which including a 200 watt oil pan heater, and four cylinder head heater at 100 watt each. That's the most powerful installed heater I can find. I do have a engine blanket as well. Beside all the, I have a 1500w car heater that can be tucked inside the cowl intake to provide more heat, or used to heat the cabin. I suppose there is really nothing I can do about those grease in the gear or other places, but if someone is flying in -30c, regardless if it previously parked inside a heated hangar or not, these unheated part will become freezing cold real quick.

I guess in that case, you’ll need to do a really thorough preheat on the engine, ideally starting the night before. Have you got cowl blankets and stuff? Also try to preheat the interior to protect your avionics, plastics, etc. Ground lean the engine out after start and get it as hot as you possibly can before run up and subsequent application of takeoff power. You should see an initial rise in oil temp, then a drop as the vernatherm opens and allows cold oil to circulate back into the engine and through the cooler, then another rise in temperature which would indicate all of the oil is now flowing properly through the engine. Once the oil is hot cycle the prop a few times and observe the oil pressure drop and rise, too high of oil pressure is just as bad as not enough. You can blow out your oil filter and engine seals. If the battery is in good condition, it should be able to start the engine no problem, maybe give it an 8-10 second prime. Oil pressure with that thick of oil may be very slow to rise on startup, so keep an eye on it. If you don’t see any within 15-20 seconds, shut it down. The book says 30, but I always thought that was way too long. Once she’s hotted up and you’re airborne, you’ll want to lean in the climb and aggressively in cruise to keep the temps up. Running too rich in the winter keeps the engine too cold and can lead to a lot of corrosion inside. Enjoy the crisp, cold air!

I suspect that the vernatherm is headed south. They don’t always open correctly when they start to fail.

My temps have always run low. CHTs on the above trip were something like 280F max (in cruise). My oil was running around 155F in cruise. Evidently the baffling and sealing are excellent, and all that without cowl flaps on the O. The oil temp is too low (I have installed a non-factory small oil cooler plate). I need to install the large (standard) plate, but even then, oil won't get much over 170 in cruise. We've checked the sensor accuracy and vernatherm. Highest I ever see is 200F right after runup. I have 250 hours on an overhauled engine. Even in summer, most I've ever seen is 380F max in climb out and that was only because I forgot to put the mixture all the way in prior to takeoff (grumble). Usually, this engine is maxing out in the mid-300s during summer climb (full rich on takeoff, followed by leaning to the white bar on the G1000 engine page, as I pass 1,000 AGL). That's a good point about % power and running a bit more fuel through the engine. I would definitely pick up a few knots. I, too, notice a noticeable surge of power when advancing the mixture from 50 LOP. So far, this engine seems to be a textbook example of George Braly's and Mike Busch's applied engine theory. Ed

If it is in the green arc on your oil temp gauge then you're fine. The indicated temp is the temperature coming out of the cooler or the bypass from the vernatherm. It's much hotter returning to the sump.

I've had my '70F for over 7 years and the oil temp has always run hot. 220-230 in the summer and 200-210 in the winter. Below is from a flight a few days ago and you can see it 'stabilizes' at 208. Over the years I've replaced baffles, overhauled the oil cooler, replaced the oil cooler lines, and the vernatherm. ALL to NO avail You can see the vernatherm actuate at right around 180, like it should. But the temp then just keeps right on increasing! Any ideas on how to determine if any oil is actually FLOWING through the cooler? I'm beginning to wonder if that is the problem.

Liquid cooled engines maintain almost an exact temperature to the point most cars don’t even have a temperature gauge anymore. Air cooled engines are wildly impacted by the temperature and the flow of air. There is no thermostat to regulate the temperature (vernatherm on oil cooler to some extent). I love this thread every year because it reminds me winter is here. Then I wait for its brother and the 5000F CHT while climbing out of Leadville at +25ISA, then I know it is summer. Got to say spring and fall are pretty boring.

I've had my F for 7 years and about 500 hours and the oil has always turned black rather quickly but compressions have been good (>75) and oil consumption was stable at around 7 hours/qt. Further my oil temp has always been high; 200-210 in winter, and 220-230 on hot summer days. I've tried overhauling the oil cooler, new oil lines, new vernatherm, baffles...all to no avail. #2 has always run hotter than the others and has a little oil pooling when I borescope, but never any plug fouling. At annual this past June I tried a solvent flush on #2. Now I'm seeing only 4-5 hours per quart! So, as much as I didn't want to, my plane is in the shop right now having #2 removed and sent out for overhaul. I'm crossing my fingers that the cylinder OH will fix my issues. Your symptoms seem a bit different, but are you seeing high oil temps?

Mooney M20G 180hp. Oil Temp 215 - 230 degrees CHTs 303, 330, 380, 360 EGTs 1250, 1330, 1410, 1370 Powerflow exhaust Guppy mouth closure So last August 2023, I started to burn more oil in cylinders 2 & 4 so I decided to hone the cylinders and put new rings and pistons in (the A&P did it). I went through the break-in process and everything seemed normal. I ran the engine rich and kept the CHTs and EGTs as low as I could get them. I have about 40 hours on the new rings and pistons and oil consumption stabilized. However, now at around 60 hours I have started to burn a lot of oil (about 1.5 Qt in about 3 hours) and getting worse. Ugg! So I thought maybe I glazed the cylinders. So I had the A&P check it out. Before they did anything they took a compression test on 2 & 4, both were 72/80. When they pulled the bottom plugs #2 looked okay, but #4 plug was oil soaked and there was oil pooled in the cylinder. Another complaint I had, was that it seemed my oil temperature was running hot. This used to be a cool running engine. I replaced the oil cooler with a new high efficiency, which helped some but still running hotter than I would like. Now my oil temp is around 215 to 230 degrees in level flight (more towards the 225 range at 8000ft). I thought about replacing the vernatherm... What concerns me the most is the condition pistons after 60 hours. Notice in the pictures there are scraps on the piston walls and one looks like it got too hot. The cylinder walls look good with no scaring. I am wondering how this could happen? and how to prevent it from happening again? I thought I would solicit thoughts from the collective group. Thanks Neal

Hey guys, I have a low oil temp issue (engine is not running cold, like 380F) and OAT is 26C (hot Houston summer). Oil temp at cruise is 140F (at 25in/2500RPM). I want to take out the vernatherm to see if it is stuck open. I've read the maintenance manual for Lycoming IO 360, and I think everything is pretty straightforward. My only doubt is, do I need to drain the oil? When I removed the pressure relief valve, I did not and everything was fine. But the Vernatherm is closer to the oil filter and I'm not sure if I'm going to get a bunch of oil when I remove it.

Since this post, my A&P has flushed the cooler - found no concern or debris. He also tested the function of the vernatherm and that looked good. The oil lines are from 2021 and seem to be in good order. He did find one thing - I have the oil filter relocation STC. This leads to a connector being mounted to the back of the engine where multiple oil outflows exist. The incorrect gasket was present, blocking about 40% of the larger oil flow hole (pardon my lack of vocabulary on this). We are waiting for the replacement gasket to arrive.

Rumor is that about half have that and half don’t. Mine doesn’t have it but I have normal 185ish oil temps. Did you check your vernatherm? When was the last time the cooler was flushed out?

After an overhaul I have 220-230 oil temp. Removed oil filter adapter and tested brand new vernatherm - doesn’t fully close when boiled together with oil filter adapter. Same with old vernatherm that worked perfectly before overhaul (it has a nice ring indentation indicating it worked previously). Both open up a bit less than 1/4 inch. Same with another brand new oil filter adapter. Now I am scratching my head, 2 vernatherm, 2 oil filter adapters - what’s wrong? There is also one washer installed between vernatherm and oil filter adapter Q: is washer between vernatherm and oil filter adapter required? Removal would solve the issue Q: any potential gotchas testing vernatherm in water vs oil? Curious if oil provides some additional qualities that help vernatherm open up?

@lithium366 Thanks! Interesting, because my theory has been oil isn't circulating through my cooler for whatever reason. Your observation tends to say something is making my oil very hot; past the ability of the oil cooler. I have good compressions and use 1 qt every 7 hours so I don't think blow-by is responsible...no idea where to look. I did find in my research that engines without an oil cooler may have a plug, spring and plunger installed where the upper oil line ("A" in Lycoming diagrams) would attach. If only the plug and spring were removed (and the plunger left at the bottom) when the oil line was attached I could see that blocking any flow to the cooler regardless of the vernatherm. Maybe something to check?

Yep so you see that flat area at 185 - this is due to vernatherm opening and colder oil from hoses and oil cooler mix with hot oil, delaying further oil temp raise. When you have issues with vernatherm, hoses or oil cooer (like I do) that flat area is non existent or very small for me it looks like your vernatherm is functioning well and problem is something else

You could call Lycoming tech support. Since you have the old vernatherm, you could try swapping it and see if it makes a difference.

Both vernatherms I have Lycoming and Superior stamped 85 C. That’s 185F and that’s about the temperature they “mostly” closed. They continue to expand at a much slower rate until water boiling temp. It’s interesting Lycoming mentions other temps I sent oil cooler to overhaul during engine overhaul, it’s hot to touch after flight but perharps vernatherm only partially open allowing temps to go up

From my notes at the Lycoming factory class: #1 cause of excessive oil temperature is vernatherm. It should begin to expand at 150 degF and should be max expansion (>= 5/32") at 170 degF. Also check that Vernatherm doesn't have a break in the seal of the cone to the seat. Other causes: restrictions in oil cooler hoses, blocked airflow to oil cooler, oil cooler needs overhaul due to trapped contaminants.

I've fought this issue for the nearly 7 years I've owned my F. So, I'm REALLY interested in what you find out! But you may be on to something with the valve not seating completely. However, my understanding is that it seals off when HOT, which forces the oil out to the cooler. I had the oil cooler overhauled, replaced the vernatherm, replaced the hoses to and from the cooler, new baffles...oil temp still runs 220-230 on hot days. I've been trying to figure out how to independently verify that oil is actually flowing through the cooler. I went so far as to buy a two channel temp probe and tried to instrument the input and output fittings of the oil cooler. Unfortunately, that didn't really work; the probes need to be INSIDE the lines to directly measure the oil temp; no way to do that.

Cyl temps are normal, I checked inter-cylinder baffling. I am convinced the issue is vernatherm / seating - you can see a light going thru the seat. That should be fully closed?

Yes, that is about what I remember, so the vernatherm is probably not the culprit since you tried two of them, baffling makes a huge difference, check temp sensor

To my knowledge vernatherm should fully open 180-190 degrees so you oil doesn’t get hot Savvy also thinks it’s a vernatherm issue based on data they see (oil temp flat is too short when vernatherm opens up)

OAT is lower on the bottom plot. On Lycomings the oil goes through the cooler first, before it gets to the pressure regulator. The regulator (relief valve, actually), and vernatherm should still work basically the same, but they're not precision devices. It could even be just the different batch of oil was a bit different in viscosity or something, or some combination of small factors.

This is on my list to do. Something I noticed that vernatherm gasket seem to be thicker than the one I previously had, I am thinking of taking an entire oil filter adapter with vernatherm and throwing it into a hot water monitoring temps and how it seated and how it closes. Open to any better ideas tho

Okay so I did a supervised overhaul with my A&P due to cam being worn on #4. Engine now has 8 hours but there are some persistent issues I am seeing, curious if I can use your brains. 1966 Mooney M20E, IO-360-A1A 1. Brand new PCU-5000 governor was installed during overhaul (old governor was contaminated and unrepairable). Before overhaul prop did not overspeed, after overhaul it is kinda lagging going into 2750-2780 and then coming back at 2700 limit. I also see RPM fluctuations in bumps, and while transition to a climb and descent. Propeller is a 3 blades hartzell installed new in 2000 and never overhauled (960 hours on prop). Some suggest to overhaul prop in case there is friction there but curious what other think 2. Oil cooler is cold to touch. Oil cooler was overhauled and flushed. Not like cold but more like ambient temperature. It should be hot on temps above 185 when vernatherm opens? Wondering if it is working. Brand new vernatherm was also installed during overhaul. Oil temps are in 230-235 in cruse but I don’t pay much attention to oil temp yet since I only 8 hours on overhauled cylinders 3. #1 induction leak. Small RPM - 150 degrees higher EGT than other cylinders, cruise RPM - same EGT as others. I replaced rubber seal and used gasket maker on the paper gasket. Re-did this twice, #1 still has the same induction leak. Where else it can leak from? New injector nozzles with nearly equal flow. fuel flow divider was overhauled as well (I thought maybe below 8gph fuel flow divider can fake induction leak by spraying less fuel than at higher fuel flows when it no longer controls fuel)