Oil temperature question
 

As long as I've been flying my 7A, the oil temps have always been low. I even have a small airflow restrictor plate over the bottom third. My temps typically ran in the 160's range. CHTs are all 350's or little less. I was recently watching one of Mike Buschs online videos and he mentioned that the oil temps we see are coming from the coolest oil in the engine, (because it's oil coming back from the cooler), and that the actual temps can be 25-30 deg hotter. My oil temp probe is mounted where the Lycoming manual calls for it to be. I recently changed oil temp probe and put in the one from dynon. It's reading 175-180 with cht's all good. If the temps inside the engine are indeed 30 deg hotter then I'm running along in the 210 neighborhood. I'm feeling a little confused on the issue. Can the VAF brain help me clear my head on this. Wonder if I should remove the small restrictor plate. Thanks for your thoughts.

All is good. You want ~180 degrees as measured on your probe. This does translate to higher oil temps elsewhere in your engine, but that is already taken into consideration for the ~180 degree target.

I typically close off some of my butterfly valve to keep at ~180.

Carl

Yes, the Lycmoning OT sensor is in an area that see's oil directly from the cooler, when the vernatherm is closed (oil diverted to cooler). So, when OT's are abover the vernatherm set point, the oil temps in the sump will typically be warmer than the oil temp at the sensor. However, when the OTs are below the set point, I would expect the sump temps to be the same or close. However, the OT sensor is showing the OT of the oil that is being dispatched to the engine for lubrication work.

No concern with sump oil temps of 210. This is well within the normal range for modern oil. This was likely known by the original designers that set the 185* vernatherm temp and this temp has provided good service for many decades. It is a compromise setting, reflecting the need to keep temps below the critical level (around 250) and high enough to remove as much moisture as possible (higher OT's equate to faster H2O evaporation).

high oil temps are MUCH worse than low oil temps and therefore don't recommend more permanent cooler blockage. I would much rather accept consistent 170* temps to ensure that my trip to OSH, with 60 minute taxi at 100* OAT's, did not overheat my oil on depature.

Larry

You want your oil to be at or about the water boiling point 212F. Oil Temp in the cylinder heads near the exhaust valves is about 30F higher than what you are reading. So 180F measured at oil temp probe near oil filter is the bottom of the normal operating.

If oil gets too hot it will coke and provide poor lubrication. Lycomings are air and OIL cooled. If the engine gets too hot of course it affects metallurgy and early wear of key components. Oil starts breaking down at 275F degrees so 245F is max red-line (but not for continuous). 165F degree is recommended Min OT for takeoff in cold weather I recall. A good range 185° to 210° F.

Good grief. Not that old notion again.

I don't think I could ever get my oil temp to 165F in a Wi winter let alone summer prior to takeoff. I've been using 100F Oil and 200F CHT as a minimum prior to takeoff.

Would like the source for that one. Lycoming manual states that if engine will take throttle application without stumbling or other symptoms, it is warm enough for Take Off. Pretty similar to every other engine out there. Though some air cooled engines warn against high RPMs at low oil temps. Not really an issue with a 2700 limit. Personally, my limits are related to cyl wall temp, guessed at by CHT's (concerned with differential expansion with piston)

Last I checked my science, water evaporates at all temperature. Even frozen water does - sublimation. Boiling water evaporates no faster than water at 210* I do beileve that the warmer the water, the faster the evaporation. Maybe that is the point your trying to make; But would like to know how much faster evaporation occurs at 180 vs 150*. I am guessing it is not as much as you think.

And...

The boiling point of water is 212F...at sea level, on a std. day/pressure. At 8500ft, boiling point of water is 196F (std. pressure). And the boiling point is phase change, not evaporation.

Some reading -- for those of you inclined: https://www.engineeringtoolbox.com/e...ace-d_690.html

Check your Lyc. manual for temps & pressure limits and use them. If Lyc. wanted us to worry about the temperature of the oil at the wrist pin on con. rod #4, or the top half of the 2nd main bearing, they would have instrumented it and put it in the book.

Generally speaking, if you follow the book/specs, your engine will be just fine. Your hair will regrow, you'll gain wealth, you'll lose weight, your kids will love and respect you...

Cheers :)

B

"Good Grief". That dismissive statement is backed up by facts? Proof please.... My comments are based on Lycoming publications. You want your engine oil temp to burn off all the moisture and acids from combustion in the oil. That will not happen efficiently unless the oil temp reads is about 180F. This jives 100% with Lycoming. Old notions rooted in fact is still as true today, where the Lycoming is pretty much the same as 1955.

Read the cold weather Lycoming bulletin. 165F is acceptable. Can you fly or take off with less? Yes. Should you fly around with 100F oil? No and if you can't eventually get 165F you should block the oil cooler.

https://www.lycoming.com/content/operating-cold-weather
Third from last paragraph.... I am not kidding, tend to go with the Manufactures recommendations. However I will concede that the bottom of GREEN for Oil Temp on most Certified Planes with Lycoming's is 60F. (some 100F). However if you want to light the fire, take off in sub-zero temps 1-minute after start, with 60F OT, up to you. Lycoming recommends 165F as a MIN operating temperature before takeoff, per Lycoming SB's, SL's and Notices. It is NOT an issue above 40F ambient temperatures. If you can't get 165F you should block your oil cooler.

You posted twice? I have a degree in mechanical engineering so I understand a little about math and SCIENCE! Also your comment ignores OT as recommended by Lycoming. The other part of your comment is irreverent to operation an internal combustion air (oil) cooled aircraft engines. We blow-by a lot of crud unto the crank case, moisture, acids, by products of combustion and raw fuel. That moisture and acids in the moisture, byproducts of combustion are "emulsified" in the oil.... Oil needs to be heated to about 210F to allow the moisture and the nasty volatilies to gas off and go out the vent. This is not opinion. It is Lycoming's recommendation and it is SCIENCE! :) Ha ha I love when people invoke the word SCIENCE as an appeal to authority.

Your sarcasm and humor noted, read my post above. I agree FOLLOW THE MANUAL. The recommended operating OT is 185-210F. Second your comment about when water boils is irreverent when water in solution with the oil. You want to get the moisture emulsified in the oil, which has acids and combustion by products in solution, BURNED OFF.... Leave that in there and let the engine sit you will have corrosion. What kills engines is disuse and not allowing them to run at full operating temperatures. However do what you like. Your engine. Cheers :-)



Fun fact I had a 1959 PA23-160 Pilper Apache with two O-320 160HP engines. I bought it around 1990 with 1800 hours since engines were new, replaced about 5 years earlier. It was flown by previous owner about 300-400 hours a year. I flew it about 150-200 hours/yr for two years and sold it with 2200 hrs on the engines. All cylinders were high 70's. I used 1 quart every 8-10 hours as long as I kept the oil level under 6 qts. This shows you what flying an engine and keeping it within limits can do to add longevity.

BTW More fun facts, LYCS with 8 qt capacity need to be run under 6 qts or less.... Why? More than 6qts will just get blown out. Why? It is a FAR engine certification requirement they have reserve oil capacity for a leak and having reserves to get on ground. With a wet sump Lycoming put that reserve oil there, which in turns increases oil consumption. It reduces overall crankcase volume, increases case pressure and oil splash, which goes out vent. You are far better putting in a PINT in at a time every few flights, verses topping 6 Qts to 7 Qts. I ran min between 5.5 to 6 qts but tried to shoot for 5.7 Qts for local. If cross country I'd fill to 6 Qts. I would put in just a tad every few hours or flight to keep that level.