A response by Flash in a seperate thread made me realize somethnig that I am a bit ashamed to admit.....
I do not know what temp (on average) oil reaches after warm-up in an "average" motor.
So, "on average" what temp range is expected to be seen?
I'd be curious to know what temp the oil is in the pan?
After passing thru an external cooler and then exiting the pump (i.e just before being put "back to work")?
Also, what are the highest localized temps oil will see?
Again, I know all these will be averages.
I'm especially curious about localized temps because I have read some interesting case studies where very high localized temps lead to a fairly rapid degredation in oil quality.
Any info, comments, discussion is appreciated (and enjoyed).

 

i know you want the oil temp to be at least 212 to evaporate water in the oil.

 

A friend of mine had a VW Gti with an oil temp guage, and on the highway, it never got above 190. As long as the oil is hotter than outside temperature moisture will evaporate. I think it would evaporate quicker the hotter it got, but as long as it's up to operating temperature, it should evaporate moisture just fine.

 

I can't say what the temp should be, but it would seem that it should be close to between thermostat temp (~195 F) and what I accept for maximum water temperature (~235 F). I think the oil temperature matters the most, and the water temp is actually secondary, but the oil temp should closely track the water temp (or vise versa). I'm not sure what "close" would actually be, but I'll soon know what the oil temperature actually is on my 4.6 F150.

I have installed a transmission temperature gauge, and got some extra probes and a rotary selector switch. Next oil change, I will put a "T" and temp probe into the oil pressure sender port at the oil filter outlet. This will give me the temp as the oil is being delivered. I realize it could be at a higher temp locally, but, with good oil flow, I don't think the difference would be great or lengthy enough to cause much coking.

I will eventually put probes in the power steering and differential oils, both of which have caused problems on other vehicles. Some may think this overkill, but actually the probes are cheap once you've bought the gauge, and it's easy to do. They wouldn't put a power steering cooler in if this wasn't a potential problem, and my horse trailer conceivably might be taxing that 8.8 rear end.

I'll post my results.

 

MrBSS is pretty close. Because oil does not absorb or release heat as readily as water or coolant, it generally will run slightly cooler than the thermostat. My 91 Bronco, 5.0, will run 170-185 F during normal operation. I has hit 225 pulling a trailer in the heat of summer.
MrBSS, I would be very interested in knowing the results of your temp installation, please post results when you have them.

 

Mr BSS, the rotary selector switch and multiple probes would make a great mod article. hope you have time to post the results and how to tips.

 

boil- i ment to say the oil temp needs to be at least 212 to boil all the water out of it not evaporate.

 

I've had oil temp gauges in a few vehicles over the years, and I've seen oil temperatures as high as 250 F when towing in hot weather - even though the coolant temps were down at 230 F or so. From what I've seen, most of the the time the oil runs at a lower temp than the coolant - but sometimes under extreme conditions it runs quite a bit hotter, and those are the times that an oil cooler would be a really good idea. In my opinion, 250 F is way too high - ideally, I'd like to see oil temps stay below 200 or 210.

However, remember that these temps aren't really the maximum temperatures the oil sees, but are merely "average" temperature readings. In certain locations (bearings, cylinder walls) the oil temporarily reaches a far higher temperature - I wouldn't be surprised at all to see temps well above 300 F, which is why you want a high flash point.

Also, most oil coolers (that I've seen, at least) are equipped with a thermostat - because you also don't want your oil to run too cold, probably not below 160 or 170 F, because then it doesn't lubricate properly or burn off the corrosive elements (acid, moisture, and so on). I've read that you need to run your oil at these temperatures (or higher) for approximately 30 minutes in order to burn off the moisture and acids that build up in the oil - simply running an engine up to operating temperature isn't enough, because you've got to keep the engine (and oil) at that temperature for an extended period of time.

LK

 

The oil temperature "green zone" in light aircraft is about 180-245F. This should at least give a point of reference. These engines, however, run SAE 50 in the summer and 15W-50 in the winter.

Jim