Oil temp too high. Is this a standard component? Or, a mod?

John Richardson

John Richardson

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John Richardson
I recently purchased a 1979 Piper Dakota with a Lycoming O-540. This plane lived in Newark for a long time, and had at least one cold-weather mod--an engine heater. I picked up the plane from Newark in April. It was very cold there. During the 10 hour trip to Louisiana, the engine monitor was happy and the analog oil gauge reading was normal. Once in Louisiana, the plane sat for 6 months undergoing an annual and a prop overhaul. It didn't fly during this time.

Fast-Forward to September in Louisiana, with a temperature of 90F. We took it flying today for the first time. During the climb, the engine monitor alerted cylinder head #4 at 462F, much higher than the other cylinders. Also, the oil temperature spiked to 260F, even after we leveled off.

We immediately landed to assess. Nothing has changed, other than spark plugs and the prop, so we are puzzled. It occurred to me that perhaps the owner in Newark had altered the baffles to keep the engine warmer. Or, perhaps the baffles are just worn and allowing leaks.

I found an odd-looking rubber flap attached to the cowling at the vent inlet. Could this be a cold-weather mod?
 

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No, that's just a part of your baffling and doesn't have to do with cold weather. It wouldn't hurt to redo the baffling, even the smallest leaks can have an effect. It also could be a burned exhaust valve causing those temperatures. Keep in mind, with a carbureted engine you might not be getting the same fuel/air mixture to each cylinder and IIRC the #4 cylinder is one of your middle ones which will be sandwiched right between two other hot cylinders. YMMV

How did your cowl flaps affect this?
 
Your baffles can use replacement or at least seal with some RTV. I see gaps in between them everywhere. With the cowl on, use a flashlight and shine the light through the inlet. You should not see any gaps in between the baffles.

That being said, I would expect that all of your cylinders be running on the high side because your baffles overall look about the same. I agree with the above post suggesting to look for something different on #4.
 
I'd be looking at the carb. It sounds like you're too lean.
 
I’d look at several things.

1) Timing. That's easy to get wrong, but can be verified in 10 minutes.

2) Do you see wear marks where the side baffle seals rest (and rub) against the top of the cowl? They look short to me. The seal over the aft baffle is how one should look. On the sides (and rear) you should see clear evidence of wear on the baffle seals and the underside of the top cowl. You can also put the top cowl on and look through the cowling openings to see if the baffles make a good seal against the top cowl. A too-short or reversed (outward bending) baffle seal will leak a lot of air.

3) If the CHT on #4 was the only one that was high, you might check the inner cylinder baffles around that cylinder. You also might look for an induction leak on that cylinder. You can also swap CHT probes between that cylinder and another to see if you have a probe or wiring problem.
 
The baffling isn’t super pretty, but it’s not what’s causing your problem. Seems like that cylinder is running way too lean. Are full-throttle fuel flows where they’re supposed to be? Are all cylinders hot, or just that one?
 
AA5Bman said:
The baffling isn’t super pretty, but it’s not what’s causing your problem. Seems like that cylinder is running way too lean. Are full-throttle fuel flows where they’re supposed to be? Are all cylinders hot, or just that one?
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Just the #4 cylinder is that hot.
 
Check for a lead clinker in the bottom plug.
 
John Richardson said:
Just the #4 cylinder is that hot.
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How hot are the others?

That oil temp is telling a story. That engine is burning itself up. One cold weather mod that most pilots do is restrict air through the oil cooler during winter months. The popular tool for that is duct tape. Make sure the oil cooler isn’t partially blocked. If it is? Fire your mechanic who did the annual. All this may be on him anyway. Why it was fine before annual and smoking hot now would have me looking at everything he did.
 
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I don't think it is a big deal, but I just noticed something about your baffle seals. They are "tucked" the wrong way. Starting with the front left seal coming off of the inlet, where the next one overlaps, it should be behind the front seal (between the front one and the aluminum baffle). They should be like that all down the sides, but it is most important in the higher velocity areas near the inlets. This keeps the seals from lifting and creating a gap due to airflow.

And the more I look, the shorter some of those side seals appear, but again, you can check that by looking in through the air inlets
 
Looks to be time for new baffle seals. They are starting to curl at the back, indicating age. Don't skimp, buy the good (expensive) material. The mx manual should show how they are all supposed to fit. Rule of thumb is the material should lie towards the area of higher pressure so they are pressed tight to the cowl.

Make sure the inter-cylinder baffles are in place. They direct cooling air between the cylinders and if missing, can create a leak causing loss of cooling.

PS Prop lockwire is coming off from around the nut. Lock wiring those props suck, but should be better than that.
 
Looking again, the baffle seal job looks poorly done. A tywrap is not normally used to tie pieces together. The overlaps are wrong, as previously mentioned.

Baffle and seal fix would be a good place to start. Get someone who gives a hoot to clean it up.
 
Look at the underside of your cowling. You should see rub marks where the vibrating baffles have scraped through the primer. If those rub marks are not shiny or appear to be dusty or gritty, your flexible baffling is not making a good seal. Also look for grime streaks on cowl underside indicating pressure leaks from between/over your baffles.

After replacing the flexible baffling, consider running a few widths of metal foil tape on the cowling underside to protect the cowling from further damage. The baffling should seal against the tape.
 
A missing intercylinder baffle might be at fault here, but that usually heats up two cylinders, not one. Bad baffling or baffle seals will affect the whole engine, not just one cylinder.

Goofy instrument readings are sometimes a result of poor engine electrical grounding. Alternator ground currents find their way into sensors and mess things up. Might even be a chafed #4 CHT lead grounding.
 
PaulMillner said:
That would make that cylinder run cool, not hotter...
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Preignition makes a cylinder run hot. Clinkers can act like glow plugs. Might want to take a real close look at the new plugs in the jug too for insulator cracks, but even 462 is a little cool for that.
 
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I plugged a few holes in the baffles and cleaned the cooling fins on the cylinders. Took it up the next day and the numbers were perfect. So, the problem has mysteriously vanished. Could sitting up for 6 months have caused a hot cylinder on first run?

thanks everyone for your feedback.
 
John Richardson said:
I plugged a few holes in the baffles and cleaned the cooling fins on the cylinders. Took it up the next day and the numbers were perfect. So, the problem has mysteriously vanished. Could sitting up for 6 months have caused a hot cylinder on first run?

thanks everyone for your feedback.
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Sounds to me like an intermittent electrical glitch. Most (around 90%) of engine problems are electrical. Ignition, intrumentation, power generation...just wait unti we have EFI:cool:
 
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