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Lycoming Operating Temperatures

N941WR

Legacy Member
There have been a lot of discussion regarding high CHT’s.

The following numbers come the Lycoming Operator’s Manual for both the (I)O-320 and 360 Parallel and Angle valve engines and the IO-390:
(I)O-320
(I)O-360
IO-390

CHT’s
GENERAL RULES:
"For maximum service life, cylinder head temperatures should be maintained below 435°F (224°C) during high performance cruise operation and below 400°F (205° C) for economy cruise powers.)

Elsewhere in the manual (section 3, at the bottom of each page.):
"For maximum service life of the engine maintain cylinder head temperature between 150°F and 400°F during continuous operation."

Parallel or Angel Valve (I)O-320 and 360: 500°F (260°C) max temp
IO-390: 475°F (246°C) max temp

Time timing advance can have a significant impact on CHT’s. This is a big deal and it continues to surprise me how a few degrees too much advance can significantly raise CHT's.

Oil Temperatures:
"Oil Temperature: The maximum permissible oil temperature is 245°F. (118°C.). For maximum engine life, maintain desired oil temperature is 180°F (82.22°C)."

I have never been able to find a minimum oil temperature; however, I did find this:
"(e) Engine is warm enough for take-off when the throttle can be opened without the engine faltering."

From the (I)O-360 Lycoming Operator’s Manual, Page 3-11:

" * - Engine oil temperature should not be below 140°F (60°C) during continuous operation."

The IO-390s have a 10°F lower Max Oil Temp than the -320s and the -360s do. From the IO-390 Lycoming Operator’s Manual:

"(f) Oil Temperature: The maximum permissible oil temperature is 235°F. (113°C.). For maximum engine life, maintain desired oil temperature is 180°F (82.22°C)."

Thanks Carl!
- Note, this is continuous operation, not takeoff, climb, or decent. According to the Lycoming rep I spoke to years ago, this is the minimum temperature at which water will boil off. (The temperature probe is up higher in the engine and doesn't record the max temperature elsewhere in the engine or oil sump.)

(If any of you can find a minimum oil temperature for an (I)O-320, let me know and I will update this.)

Based on the above, having your CHT's rise above 400°F in climb is not an issue, as long as they drop back down in cruise.
 
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Climbing out of GMU two days ago on a 90F day, my #4 and #3 peaked at 415F. I increased my airspeed to 120 Kts and that helped. In cruise the CHTs were 360 (1&2) and 380 (3&4). Oil temp was 190F. O-290-D2.
 
One of the parameters that control min oil temp on takeoff is oil pressure. If the oil is to cold, the pressure may go beyond max limits. Bad stuff can occur if that happens.
 
My IO-360 oil temp got up to 235F today flying in some hot weather over the Sacramento Valley. This was in climb. At cruise it hovered around 220-225F at 7500 feet. The air was still rather warm at this altitude. I checked my POH which lists 220 as caution and 245 as max. I had never seen the temp get this high before. Should I be concerned? Should I avoid this airmass and maybe stick to the coast for my trip back? My plan was to make a precautionary landing at 240 and stick to flying in the early morning or evening if that happens.
 
More than 1 way to lower oil temps

I’ll let other experts chime in on lowering temps but some solutions can be:
More / better airflow to the cooler
A bigger cooler
Higher airspeed in a climb
Reduced power in cruise
Etc…
 
My IO-360 oil temp got up to 235F today flying in some hot weather over the Sacramento Valley. This was in climb. At cruise it hovered around 220-225F at 7500 feet. The air was still rather warm at this altitude. I checked my POH which lists 220 as caution and 245 as max. I had never seen the temp get this high before. Should I be concerned? Should I avoid this airmass and maybe stick to the coast for my trip back? My plan was to make a precautionary landing at 240 and stick to flying in the early morning or evening if that happens.

Is this new and different? Put another way, given similar power settings and OAT, are these temperatures typical?

I watch for change. When something suddenly goes outside the norm, concern is warranted. On the other hand, if you see these numbers on a regular basis, well, it's just a system which cools poorly. It should cruise in the 180's.
 
Lycoming Operating Temps - oil temperature

Here is something I learned about low oil temps when taking my air-cooled VW Bus across the country in the winter of 2004: Low oil temps rob power. Noticeably. It was a 15K mile road trip and I had lots of time and opportunity to experiment with oil viscosity and various efforts at raising the oil temperatures. Additionally, the really fast guys in the Formula One class at Reno are reported to have "bladed" their crankshafts to reduce the effort of the crank as is spins through the oil bath in the sump.
 
Here is something I learned about low oil temps when taking my air-cooled VW Bus across the country in the winter of 2004: Low oil temps rob power. Noticeably. It was a 15K mile road trip and I had lots of time and opportunity to experiment with oil viscosity and various efforts at raising the oil temperatures. Additionally, the really fast guys in the Formula One class at Reno are reported to have "bladed" their crankshafts to reduce the effort of the crank as is spins through the oil bath in the sump.

Most production cars have one or several windage plates or trays in the sump area to minimize the drag from oil mist. The racers take it to extreme levels. Many autos have gone to 0w30 or 5w30 weight oil to help meet mileage standards also, so not a unique revelation, but very on point. It's a delicate balance though, as the thin oil has some drawbacks.

The very worst thing you can do in this area is fill the sump so full that the crank weights hit the oil bath as they spin. Not only does it create major drag, it also cavitates and foams the oil (looks like a chocolate slurpy), reducing it's ability to lubricate. I try to tell people this when they put 9 or 10 quarts of oil in their Lyc, but most tell me it is not possible for me to know more than Lyc as they give me a dirty look.

Larry
 
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Is this new and different? Put another way, given similar power settings and OAT, are these temperatures typical?

I watch for change. When something suddenly goes outside the norm, concern is warranted. On the other hand, if you see these numbers on a regular basis, well, it's just a system which cools poorly. It should cruise in the 180's.


It’s new but the explanation is that I have never flown this plane in this climate before. This is the first time I’ve flown at this OAT for any significant duration. I am going to verify that temps are back to normal once I’m somewhere cooler. Maybe there are some modifications I can make for hot weather flying?
 
It’s new but the explanation is that I have never flown this plane in this climate before. This is the first time I’ve flown at this OAT for any significant duration. I am going to verify that temps are back to normal once I’m somewhere cooler. Maybe there are some modifications I can make for hot weather flying?


Have some fun learning what the issues are and make appropriate changes based on some data and experience of others.

1. Evaluate what the cause is - excess heat rejection -overly advanced timing etc. or if you have low cooling air flow. It could also be a full power mixture leaner than necessary.
2. Seal/improve your baffle to cowl seals.
3. Seal leaks (RTV) around the engine that allow ANY air to by-pass the engine fins and oil cooler. ( might just do #2 & #3 w/o data)
4. If not good enough or lack of progress , follow DanH's instructions for installation of piccolo tubes (or alternative) and measure upper and lower chamber pressures.
5. Post pressure/speed and CHT data so others can help. Act on proven changes.

Just a thought.
 
Oil Temp

Is this new and different? Put another way, given similar power settings and OAT, are these temperatures typical?

I watch for change. When something suddenly goes outside the norm, concern is warranted. On the other hand, if you see these numbers on a regular basis, well, it's just a system which cools poorly. It should cruise in the 180's.

Agree with Dan that "change" is the key, although in this case there is a potential environmental contributor. Before getting too crazy with changes in oil cooler, baffling re-work (unless it needs it anyway), etc..., I'd also consider the possibility of a sender that's beginning to fail, or a loose connection between the sender and the EIS. I've recently had a couple of occurrences where the oil temp stays at 59 degrees (the lowest it will display) for a few minutes after start-up, then "jumps" to the expected 100 or so about the time for the run-up. On a flight Sunday, all was normal--oil temp right at 180. While in cruise it suddenly fluctuated between 160 and 180 a few times. No way the actual oil temp changed that rapidly. I ordered a new sender to have at the ready whey I open the cowl. Seems that it's likely either the sender itself or a bad connection.
 
Agree with Dan that "change" is the key, although in this case there is a potential environmental contributor. Before getting too crazy with changes in oil cooler, baffling re-work (unless it needs it anyway), etc..., I'd also consider the possibility of a sender that's beginning to fail, or a loose connection between the sender and the EIS. I've recently had a couple of occurrences where the oil temp stays at 59 degrees (the lowest it will display) for a few minutes after start-up, then "jumps" to the expected 100 or so about the time for the run-up. On a flight Sunday, all was normal--oil temp right at 180. While in cruise it suddenly fluctuated between 160 and 180 a few times. No way the actual oil temp changed that rapidly. I ordered a new sender to have at the ready whey I open the cowl. Seems that it's likely either the sender itself or a bad connection.

This is another possibility. My OAT probe for example is completely inop. Will fluctuate between -31F and 57F in cruise. So it’s common and possible that these probes just fail. Probably worth putting a new sender in just to be safe.
 
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