Scary High Oil Temps - Lycoming 540

High oil temperature and oil leak I am dealing with now. Did a compression check and one cylinder was 20/80 with blow by past rings.
 
Oil cooler didn't fix the issue.
Now looking at the baffling. MX was supposed to replace baffle seals last week but I can't get him to get me on his schedule.

I am bringing an electric kettle out to the plane to check the probe but I suspect it is fine.



What else might cause the high oil temps? Vernatherm and cooler replaced. Baffling is next but it is in no worse shape than when I bought the plane. It is not great but not terrible either.
 
How are your CHT's? Any change there? That might be an indication of a baffling, timing, or mixture change.

Any indication that you're getting more blowby through the rings?
 
Since the oil is darkening faster than usual it does seem that something is getting much hotter (duh, but it is a clue) vs gauge. But def check gauge.

If not the gauge I feel like its oil pump related and last oil change caused something to reduce flow but still have pressure...if that is possible.
 
I had this issue and it turned out to be a failing cylinder that was blowing a significant amount of combustion exhaust into the crankcase. Eventually the cylinder seals completely failed and my oil temp gauge hit redline, forcing an emergency landing. I had noticed that the oil was getting dark quite quickly, but attributed it to just being an old O-200. Replaced the failed cylinder and everything went back to normal.
 
kyleb said:
How are your CHT's? Any change there? That might be an indication of a baffling, timing, or mixture change.

Any indication that you're getting more blowby through the rings?
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I don't have any sort of engine monitoring so I have one CHT gauge and it doesn't seem overly high
 
AvNavCom said:
I had this issue and it turned out to be a failing cylinder that was blowing a significant amount of combustion exhaust into the crankcase. Eventually the cylinder seals completely failed and my oil temp gauge hit redline, forcing an emergency landing. I had noticed that the oil was getting dark quite quickly, but attributed it to just being an old O-200. Replaced the failed cylinder and everything went back to normal.
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This is something that would be caught on a compression check right?
 
So I went out and tested the actual oil temperature probe tonight..

I would say that it's reading a little high. I put boiling water in a container and stuck the probe in it and then went around to the panel to look at it so let's say there was a 2 minute delay between the water boiling and me seeing the panel.

At a cursory glance, I would say it's reading higher than 212° and the water had probably already cooled a little.

But I wouldn't say this means the probe is bad.

20240629_210218.jpg
 
AV8R_87 said:
Get a cheap IR thermometer and measure all four cylinders after landing. See if one is significantly hotter.
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Curious - what does it indicate if one is hotter? Also, what about the other two cylinders? ;-)
 
I just helped a friend that has a -180, so I was stuck in 4-cyl mode. I agree, worth checking the other two so they don't feel left out.

It's related to the above comnent of checking if one cylinder is unhealthy and the fact that he doesn't have an engine monitor. If a cylinder is running hotter for any reason (induction leak, for example), it would be a quick way to find out.
 
Check the timing. I can never recall which way is which. But if the timing is off one direction, you raise CHT some, lower EGT and increase blow by. The other direction, you can lower CHT, increase EGT and decrease blow by. The really fun part is when you get two mags drifting in opposite directions.

When checking the timing, what matters is the actual spark time, not what the gear index shows. I forget how to do this, so someone else might post the info; but make sure your mechanic does it completely and correctly. I had a mag which caused higher CHTs by having an internal slip in the plastic gears, and the oil was slightly more burnt and changed color must faster. I recall the mechanic wanting to change the oil at the same time due to that.

Tim
 
Aging mag can advance timing. Advanced timing means more time for hot combustion gas to warm CHT.
 
I thought that problem was oil temp…
 
SebIp said:
I thought that problem was oil temp…
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Advanced timing can heat the entire engine, including the oil. Unfortunately, Bryan has an analog oil temp gauge, so it is hard to objectively determine whether he's seeing a "normal" slightly higher oil temp due to higher OAT or if something has changed. CHT's might give an indication.

I'd be very inclined to listen to anything Dan Thomas has to say on the topic.
 
SebIp said:
I thought that problem was oil temp…
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Indeed. I'm a big fan of approaching problems like these as systematically as possible. Mike Busch has some great articles/videos regarding using the differential diagnosis approach (and as a physician I completely agree it's the best way) rather than changing things out in the hope of finding the "thing" or doing things based on hunches.

In this instance, I would recommend defining the problem as precisely as possible (chief complaint: oil temp reading is higher than expected) and then sit down with a mechanic and try to think of every possibility that could cause such a thing to occur and do so in a logical manner, perhaps starting at the gauge itself (e.g.: bad display, bad transmission of data, bad probe creating the data, etc.) until you have a list of every reasonable possibility that could overheat engine oil. Then start eliminating possibilities based either on facts or non-invasive testing. You have already done some of this with advice from above but I think it's worth really taking the time to list everything out beforehand and then scratch things off as you go along. Once you've eliminated all other possibilities, whatever remains must be the truth.

SixPapaCharlie said:
This is something that would be caught on a compression check right?
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Yes, but don't rely on your most recent annual to eliminate that possibility. My aircraft passed compression checks perfectly and then three months later the seals blew and pegged the oil temp gauge. It sounds like this reading change occurred relatively quickly, rather than being a slow onset. This suggests a quick failure (or incipient failure) of something to me, rather than a slow clogging or degradation. In my case, I noticed higher than normal temps for about a month which I attributed to the California Central Valley being an oven-baked hellscape in the summer before the complete failure occurred. In retrospect, the high oil temps were my indication that a cylinder was about to let go.
 
So I just flew for about 40 minutes. It never got in the red but it got uncomfortably close.

I landed and shot the IR thermometer at the cylinders All of them were between 200 and 240° just shooting it at the fins.

The only anomaly I noticed was when I shot the thermometer near the exhaust port on the cylinders they were all still in that 200 to 240 range The front left cylinder in that one area jumped up to 370.

Every other part of the cylinder was in that 200 to 240 range but something was super hot right near the exhaust port on that cylinder.
 
In order of accessibility to the normal human (not an A&P) depending on tool availability:

-Cut the filter to look for excess metal (friction derived heat).

-Borescope for anything obvious (cylinder wall issues).

-Leakdown test

-Mag timing

Not sure if cylinder leanness caused by fueling (clogged injector or induction air leak) would cause high oil temps, unless maybe across the board on all cylinders?
 
455 Bravo Uniform said:
In order of accessibility to the normal human (not an A&P) depending on tool availability:

-Cut the filter to look for excess metal (friction derived heat).

-Borescope for anything obvious (cylinder wall issues).

-Leakdown test

-Mag timing

Not sure if cylinder leanness caused by fueling (clogged injector or induction air leak) would cause high oil temps, unless maybe across the board on all cylinders?
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Due to excessive flying, I am changing my oil a lot. I haven't noticed any alarming chunks of metal in the filter, Just the typical glitter from time to time.
Annual is in July so I am hoping to get this in the hands of my normal MX rather than me and the guy looking over my shoulder guessing at this.
 
Dan Thomas said:
A poor engine ground to the airframe can do it.

The alternator causes electron flow from the bus, through the alternator to the engine ground (or to airframe ground via a dedicated alternator ground cable), thence to the negative battery post, through the battery (which charges it, since this flow is reverse to normal battery discharge flow), and out of the positive battery post to the bus.

Now, the oil temperature sensor is a brass fitting that screws into the oil filter housing. It has one terminal, which leads to the oil temperature gauge. The other side of the oil temp gauge goes to the bus. The bus power pulls electrons through the gauge, which gets them from the engine crankcase vie the sensor, which has a resistor in it that lowers its resistance when it gets hot.

If the alternator is not well-grounded to the airframe, those electrons from it like to find other paths to the airframe, and one of those paths is through the oil temp sensor and to the gauge. This increases the electron flow through the gauge, spiking it.
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Would that result in a different temperature reading between engine running/ charging vs engine stopped?

I would think that once the engine is warmed up, one could compare the indicated temperature just before and after shut down. That should be a rapid change compared to the time it takes for things to actually cool down.
 
Capt. Geoffrey Thorpe said:
Would that result in a different temperature reading between engine running/ charging vs engine stopped?

I would think that once the engine is warmed up, one could compare the indicated temperature just before and after shut down. That should be a rapid change compared to the time it takes for things to actually cool down.
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Yup. I mentioned that on another oil-temp thread. In post #25 of this thread I suggested this:
Dan Thomas said:
Another way of proving it is to load up the alternator in flight and see what the temp needle does. More current will mean more gauge error if the grounding is bad.
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Okay so I don't believe my test yesterday was super accurate because I was pouring water into a container and then putting the thermostat into it.
Today I took the gauge and the thermostat home taped a 9-volt and two one and a half volt batteries together to create a 12 volt circuit and I put the probe in water that was actually boiling.

It pegged well past the red. But I also don't know what I'm doing.

I tested the temperature of the water and it was 212°. I made sure the circuit was going the right direction if I reversed it it went all the way down to 0°
so the thermostat seems to be doing what it's supposed to be doing but it does appear to be reading incredibly high in this kitchen setup that I've made.

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I bought another gauge from sporty's and put it in the same water and it's reading 212.

While the engine was hot today I pulled off the existing gauge and plugged in the sporties gauge and it read significantly lower.
I do believe what I have here is a gauge or thermostat that has gone bad.

I'm still going to do a compression check just to make sure the cylinders are okay given that that one exhaust port on one of the cylinders was reading significantly higher.

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In hindsight this would have been a good place to start as it would have only cost me 200 bucks. I think I'm about $1,200 into this fix now

That said replacing anything isn't a bad idea. My oil cooler was looking a little rough
 
Nice! Hope everything is good once you have it put back together.
 
I think the oil cooler replacement was a good idea regardless. Not just rough, but would have eventually led to a larger issue; and potentially catastrophic.

Nice catch on the gauge issue. Sensor problems are some of the cheapest things from a material standpoint, just usually a crap load of labor to chase down.

I am too lazy to go back and read the thread from the start. But I believe there were a couple older mechanics on here who said check the gauge, check the gauge!

Tim
 
tspear said:
I think the oil cooler replacement was a good idea regardless. Not just rough, but would have eventually led to a larger issue; and potentially catastrophic.

Nice catch on the gauge issue. Sensor problems are some of the cheapest things from a material standpoint, just usually a crap load of labor to chase down.

I am too lazy to go back and read the thread from the start. But I believe there were a couple older mechanics on here who said check the gauge, check the gauge!

Tim
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Yup. I know. But I am actually doing this with a mechanic and he wanted to start with the first 2 items. The first one, Vernatherm was quick and easy. And I think the oil cooler needed to be replaced anyway so I'm not irritated about it being something small. Looking under my cowl, replacing any piece of it would not be a mistake. It's a little rough.
 
For whatever its worth, the chain of events here made sense and I think the end result is a much better result than if you had just gone straight to the gauge and said "Problem solved".
 
If the temp gauge is the issue at least it led you to find other issues (oil cooler) that could have created a more serious event later. Better to address than ignore.
 
Did you use the same temp probe for both the OEM and Sporty gauges?
 
So I guess it could be the gauge or the thermostat but I'm just going to replace both
 
Those old temp gauge systems worked like this:

1720196398145.png

The battery fed both coils. One coil had full electron flow all the time, and the other was varied by the temperature sensor (probe). This diagram is lacking the ballast resistor that such systems had, and that resistor was in the ground line where I have the red circle. That limited the authority of that electromagnet so that the other could move the gauge toward Hot as the sensor's resistance decreased. The resistor would have a resistance about the same as the midpoint of the sensor's normal range. That would put the needle about center at the middle of the sensor's range.

The lack of the resistor in this diagram may indicate that the constant-flow electromagnet was smaller and had less authority to begin with.

If your gauge has the resistor, it may have broken down with age. Those old resistors were just a tiny carbon slug with wires at each end, encapsulated in a clay or phenolic covering. Vibration, heat and corrosion all take their toll, and a failing resistor would put the gauge indication way high.
 
Dan Thomas said:
Those old temp gauge systems worked like this:

View attachment 130993

The battery fed both coils. One coil had full electron flow all the time, and the other was varied by the temperature sensor (probe). This diagram is lacking the ballast resistor that such systems had, and that resistor was in the ground line where I have the red circle. That limited the authority of that electromagnet so that the other could move the gauge toward Hot as the sensor's resistance decreased. The resistor would have a resistance about the same as the midpoint of the sensor's normal range. That would put the needle about center at the middle of the sensor's range.

The lack of the resistor in this diagram may indicate that the constant-flow electromagnet was smaller and had less authority to begin with.

If your gauge has the resistor, it may have broken down with age. Those old resistors were just a tiny carbon slug with wires at each end, encapsulated in a clay or phenolic covering. Vibration, heat and corrosion all take their toll, and a failing resistor would put the gauge indication way high.
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You know an awful lot of stuff. Did you know that?
 
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