Scary High Oil Temps - Lycoming 540

SixPapaCharlie

SixPapaCharlie

May the force be with you
Joined
Aug 8, 2013
Messages
16,415
Display Name
Display name:
Sixer
This past week we did a lot of flying and I noticed my oil temps getting really high as illustrated on my old oil temp gage.
There were times where it was touching the red.
I would throttle back, lower the nose and baby it and it would cool a little and I could keep a green gap between the needle and redline.

I noticed the oil temp issue on the flight prior to this week's trip. I did an oil change just before this trip.

IMG_5319.jpg

I also flew much higher and I noticed that helped.
In reviewing past videos I made, the needle was consistently vertical so something has changed.
I haven't had any maintenance done on the plane since annual last July so nothing mechanical has changed.

I am looking for a local MX to come help me with this but due to backlogs in the area, I want to make sure I come here and do all the wild speculation first :)

What might cause the oil temp to suddenly start spiking?
 
What aircraft?

I had a O540 in my 182RG. The oil cooler was located near the firewall with the inlet above the last cylinder on the left side. One day I noticed oil temps were higher than normal. After landing, I couldn't see anything blocking the inlet so I removed to scat tubing between the inlet and the oil cooler.

Found a bird's nest.
 
He’s in a Comanche
 
Someone once told me redline is the redline if you are below it and not over it you should be OK. Key word should. :)
 
Interesting redline on that gauge. The Lycoming Operators Manual states the max oil temp for 540s is 245* F and recommends for max engine life keeping it between 165* and 200* in level flight, cruise conditions.
 
tsts4 said:
Interesting redline on that gauge. The Lycoming Operators Manual states the max oil temp for 540s is 245* F and recommends for max engine life keeping it between 165* and 200* in level flight, cruise conditions.
Click to expand...
I know. Next time I have money burning a hole in my pocket I am getting some sort of engine monitor.
 
I’d take a look at your baffle seals to make sure they are all there and in good shape. I’d also make sure nothing is blocking the air path to and through the oil cooler.

The other thing to check out is to make sure your temp gauge is reading correctly. Maybe you have a loose ground wire at the sensor or the sensor or gauge went bad. This isn’t the likely problem given your description.
 
In addition to the other good suggestions here, I'd suggest that you have the mechanic give the oil cooler a good flush. You'd be surprised how much sludge can build up in an oil cooler over time.
 
SixPapaCharlie said:
What might cause the oil temp to suddenly start spiking?
Click to expand...
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.


Older Cessnas had mechanical oil temp gauges. These became obsolete and unobtainable, so Cessna sold a Service Kit with an electrical gauge and sender and some wire and terminals. The mechanic would install this, but problems arose. In old airplanes, there are plenty of places where grounding is less than optimal, and so the new electric gauges in the old airplanes would read falsely high. The fix was a length of 20-gauge wire and some terminals to attach it to the engine crankcase as close as possible to the temp sensor, usually at an accessory case stud and nut, and then to the gauge's metal instrument case. This removed the voltage differential caused by bad grounding and the gauge would (usually) smarten up.

But the root problem will still persist, and if it's bad enough, the massive starter current could cause expensive problems such as a fried 20-gauge ground wire, heat-damaged engine controls, and the like. Best to start with cleaning the engine and alternator grounds and see if the temp indications are corrected.
 
Is the oil level still where normally keep it or getting lower and has it quickly darkened
 
Sinistar said:
Is the oil level still where normally keep it or getting lower and has it quickly darkened
Click to expand...
It's definitely getting darker quicker than I think it should but it's not burning oil any faster than it ever has
 
Maybe the oil darkening faster than normal confirms the high oil temp is real vs a gauge issue?

What about oil pressure, was that normal? Guessing the CSP was behaving normal or you would have noticed it.

It's weird that it is in such close time to the oil change. Like it's wrong weight oil or a new/wrong filter is restricting flow. Or just happened to be enough change to start someone's earlier thoughts of the oil cooler being restricted.

I figured oil darkening earlier was more top end than other. We had bad rings in one cylinder recently and it would darken in like 2hrs and burn a quart in less than 2 hours. But never overheated.

I hope it's something on the simpler side!
 
Vernatherm replaced. No change.
Flushing the oil cooler next and replacing baffle seals while the cowl is removed.
 
Do you have an engine analyzer or another source for oil temp... or CHTs or something? I'd want to verify the gauge's accuracy. I cannot recommend an engine analyzer enough- they get your attention faster than the old needle gauges and being able to look at all the individual CHT/EGTs can save a lot of time troubleshooting.
 
cowman said:
Do you have an engine analyzer or another source for oil temp... or CHTs or something? I'd want to verify the gauge's accuracy. I cannot recommend an engine analyzer enough- they get your attention faster than the old needle gauges and being able to look at all the individual CHT/EGTs can save a lot of time troubleshooting.
Click to expand...

I would love one but $$$
 
Time for another set of oil analysis to your favourite analysis company!
 
SixPapaCharlie said:
Vernatherm replaced. No change.
Flushing the oil cooler next and replacing baffle seals while the cowl is removed.
Click to expand...
Nothing wrong with replacing seals, but were your CHT's elevated? You're likely to see that if baffle seals were the issue.
 
Capt. Geoffrey Thorpe said:
Seems to me that ground wire (even a temporary one with a couple of alligator clips) as suggested by Mr. Thomas would be a pretty inexpensive test to perform.
Click to expand...
That. 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.

We had a 172 do this in the flight school. The instructor said that the oil temp jumped when they turned the landing lights on. That's when I started thinking, and found that Cessna SK with the revision requiring the ground wire.
 
Oil discoloration faster than normal seems to go counter to a gauge issue - but it's so simple why not do it to knock it off the list.
 
Next thing to be replaced.
What say POA? Does this thing not look like it would cool your oil sufficiently?

Heck that's probably costing me a few knots :)

IMG_3081.jpgIMG_3082.jpg
 
That first image looks like that corner was really dirty or really hot.

For the second picture I'm betting a lot of ours are close to the same. I know ours looks kinda rough.

Did they detect blockage or just going for best next culprit? Seems like pretty low labor to replace?
 
I told him not to spend any time on it just put a new one in. Anything that looks like that, it's not going to hurt to replace. $500 now or $500 later.

Next is the baffling also looks like hell these three things together certainly weren't helping oil temps but hopefully fixing all three of them solve the problem I can't think of anything else
 
Last edited:
SixPapaCharlie said:
Next thing to be replaced….
Click to expand...
Good decision. I’d like to know what caused this. Since it’s not discolored, it happened after whatever event discolored that corner.
2f92ee57ff863b50e19b192fd01f7518.jpg
 
TCABM said:
Good decision. I’d like to know what caused this. Since it’s not discolored, it happened after whatever event discolored that corner.
2f92ee57ff863b50e19b192fd01f7518.jpg
Click to expand...

Oh I know what the discolored corner is... It's krylon

There are a few obvious former owner touch-ups on this plane. I can see a couple layers of carelessly applied spray paint on the metal baffling around the oil cooler
 
SixPapaCharlie said:
Oh I know what the discolored corner is... It's krylon

There are a few obvious former owner touch-ups on this plane. I can see a couple layers of carelessly applied spray paint on the metal baffling around the oil cooler
Click to expand...
Looks a lot like an oil leak
 
SixPapaCharlie said:
Oh I know what the discolored corner is... It's krylon

There are a few obvious former owner touch-ups on this plane. I can see a couple layers of carelessly applied spray paint on the metal baffling around the oil cooler
Click to expand...

I was referring to the missing chunk of oil cooler.
 
And maybe when oil is dropped, have mechanic flush oil pan as well...if all that other stuff doesn't work. Is it possible the engine driven oil pump pick up is partly clogged? Like just enough to have decent pressure bit not enough flow?

When ours ate an adapter bearing (not your case) it was interesting to see what metal particle pieces came out and were caught in the sieves.
 
You must log in or register to reply here.
Back
Top