High Oil Temp

[akloon]

I am halfway down to Alabama from Alaska, had my M7 for 3 years, and my oil temp is strangely high. I'm used to seeing around 200-220 and it's right up on the 240, just off the limit. This started leaving Kalispell yesterday and I figured it was from the climbout, but I couldn't get it to settle back down after level off at 7500. It was pretty close to 19C ambient. Good pressure, CHT at ~400, running at 23/20 at takeoff, down to 23/18 trying to cool it off, unsuccessfully. I'm in Ontario, OR, headed to Enid, OK tomorrow (hopefully). Taking off early for the cool temps in hopes I can nurse it to AL. Any speculation on oil cooler malfunctions, indicator failures, etc, would be welcome. I'm hoping it's just the hotter ambient temp in the lower 48!

Dave
907 350 7718

[210TC]

You will not hurt her at 240. Just allow more time for a gradual cool down.
After you get to altitude try leaning just above a mis and see if it helps.

[maules.com]

Dave,
your numbers 23/20 for takeoff, do you mean 23"mp/2000rpm. If so, that could be the problem.
Have you removed all AK winterization?
Is the air egress of your lower cowling nice and stiff, or can you collapse it upward in the centre with your hand?
Is your timeing correct, in the case you annualled it before leaving AK?
Last time the lower cowl was put on, did you check that the front cylinder baffling is UP half way up the cylinders, and the section above the alternater is intact and not broken off?
If you run 100deg rich of peak, that can help cool the cht which eventually brings down the oil temp. though it cost a lot of fuel.
Stop by northern CA and I'll check your temp guage for you.

[a64pilot]

I've been chasing a high oil temp problem for a while and have come to the conclusion that the oil cooling system on a 235 is, well marginal. My gauge reads about one needle width off of the red line, but a known good digital sending unit is co-located with the factory sending unit and the oil temp in cruise runs consistantly in the 20* in 85 OAT. MY cyl head temps are actually in the mid 350's, but the factory gauge indicates about 400. Running 100 ROP or 50 ROP makes no measurable difference at all at a low, 22 squared cruise on mine in either oil or cyl head temps.
I think you, like me have factory gauges that read a little high.
You can buy a IR thermometer at Sears and tell exactly what your oil cooler temp is if you are worried, or of course buy an analyzer, or of course get Jeremy to check them.
I changed oil cooler, vernatherm, hoses and my baffles are in good shape, all to no avail.
Welcome to the south, I think you will find out that is all that is wrong. Where in Al. are you going?

[UP-M5]

my oil temp reads consistently low. i have the oil cooler 50% duct taped off currently, and even on rare hot 70 degree days it will not quite get to 180 degrees indicated. i have to believe the gauge is off slightly.

[a64pilot]

My belief is that any of the gauges, not just Maule, Cessna and Beechcraft too for example are basically good for spotting trends, that is they are good to tell you it's running higher or lower than it usually does, and not much else. I don't think they are good at determining what the temp or pressure is actually. But spotting trends is actually all you need in an airplane gauge. I think we now live in a digital world and have become accustomed to more accuracy in things than is actually required. These gauges are square in the middle of an analog reality, but they are legal and they do work to a point.

[210TC]

A64,
Did you check oil temp at peak EGT or LOP?
The reason I ask is: At 100 ROP the engine is at or very close to peak HP.
Although, cylinder and exhaust gas temps are lower at 100 ROP the combustion chamber work is at maximum. Maximum Engine power means max heat into the crankcase from blow-by and piston heat transfer to the oil. If the rings are worn more than average or leaking the oil temps will go up inversely to the other two temps.
This is theory and I am looking for some facts.

[aero101]

My oil temp was right at redline as well this summer, tried new sender, then checked actual temp with IR and found much lower then indicated. Problem ended up being a bad ground at the instrument cluster. Ran a ground wire from cluster to ground post, now indicator reads about 190 in cruise on hot day instead of 240?

[a64pilot]

David, I have tried everything but LOP. My engine doesn't like LOP. It has the GAMI's and will run smooth, but the power loss is more than I can live with at 50 LOP. I won't run higher than that because I'm chicken. I won't run at peak even though it is allowed because Lycoming recommends for maximum service life don't go leaner than 50 ROP. I want maximum service life so that's as lean as I will go.
The Continental in our C-210 is a completely different story, it's seems to have less power loss LOP.
Anyway yesterday I flew for about an hour at steady state cruise at 22 squared. I got a sustained 208 oil temp at 100 ROP and 206 oil temp at 50 ROP. I don't think it was running cooler at 50 ROP, I think that two degrees is within the margin of error, so there essentially wasn't any difference in oil temp.
Interestingly enough my oil temp is not related to power as much as it is to airspeed. It get's hottest when I'm just tooling around looking for a place to land and running say 18" and 2000 RPM at 100 mph or something. Crank it up to 23 squared and 120 mph and it will actually cool down. The 29" tires aggravate the problem because they cost me 10 kts at 23 squared.

[a64pilot]

My oil temp was right at redline as well this summer, tried new sender, then checked actual temp with IR and found much lower then indicated. Problem ended up being a bad ground at the instrument cluster. Ran a ground wire from cluster to ground post, now indicator reads about 190 in cruise on hot day instead of 240?

Now that is something I can check. Mine is an 83 and grounds don't get better with age.

[210TC]

more info,

David,

This is in reference to your question about oil break down.

The result of higher oil temperature is lower viscosity. Before the
temperature gets so high that the oil would oxidize or break down other
engine operating difficulties like detonation usually occur. Extreme
high temperatures for extended periods can result in oil thickening, but
that happens over time. The aviation drain interval (usually 50 hours)
is short enough that high temperature oxidation hasn't historically been
a problem. In one of the aviation oil qualifying test, named Sequence
VIII, the lubricant runs at 275 degrees Fahrenheit for 40 hours without
significant change in the lubricants performance characteristics. That
doesn't mean that I would recommend operating at that temperature for
extended periods, but it is evidence that the oil can tolerate extreme
temperatures for short periods without significant affect on the oil
performance properties.

Are you running into some very high crankcase temperatures?

I am not sure I have answered your question completely, so let me know
if you need additional information.

Regards,
Harold Tucker
Director, Technical Information & Training
ConocoPhillips Lubricants


My notes,
Test cell shows from 220 degrees to 245 the pressure will drop .75 lbs per degree of increased oil temp 245-220=25x.75
I have seen testing that exceeded 300 degrees. DON'T DO IT

[maules.com]

To those with the O540, the lip at the bottom of the air egress should be 2", and I know a number in the early days of Maules in AK were cut back for less cooling ans actually a slight speed gain. If those AK planes are now in the lower 48, they may run hot.
The IO540 can be helped in cooling by adding a 2.5" lip at about 30deg, which also stiffens the egress tunnel. The Lopresti cowlings of partial carbon fibre tend to collapse in the centre and at the right side under the right muffler. The collapse cannot be seen of course in flight but you can push on it as in a 145mph wind force.
Another cooling flow obstruction can be the routing of scat tubing along underneath the cylinders. Of course the under cowling baffling has many gaps which can easily be seen from lack of rub marks and silicone can be applied to close the gaps.

[SkyMaule]

On the topic but not a lycoming. I too have been fighting the oil temp battle in the climb. A rich mixture in the climb helps my I0 360 continental a lot. Also, my cowl flaps were not opening up all the way. Seems better now.

[a64pilot]

Cowl flaps?

[YELLOWMAULE]

Ditto?!