My family and I could a trip up to CT to see the in-laws. Half way up we pulled over for the bathroom breaks and oil check. Well I happened to touch the oil cooler and it was just that, cool. I couldn't sense any heat at all. Now at that point we had been driving an average speed of 70 mph for 1 1/2 hours.
Anyone have any ideas as to what is going on and is this something to be really concern about. Granted it is ideal to have the cooler working properly, but is there any risk of damage to the engine? BTW this is on my '83 TD.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

Rick, based on what I have read you would have to really heat that baby up to get hot oil to circulate through the cooler. The oil filter housing has a thermostat that will open up and circulate oil through the cooler when necessary. The wording in the manual is: "At an oil temperature of 110 dC or 95 dC, depending on thermostat installed, a distinctive increase of oil temperature on oil cooler should be noticable (manually)". It goes on to describe how to test the oil cooler thermostat but you have to have something called a Telethermometer (p/n 116 589 27 21 00). I imagine that during this time of year your oil is probably not getting hot enough to require the cooler.

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Jim

Would the water temperature have to get to something like 100 degrees before the oil temperature would get to 100 degrees?

Engatwork was talking about oil temp not water temp. There is a thermostat in the oil filter housing that works similar to the cooling system thermostat. The oil only flows thru the oil cooler when it is above the temperature determined by the oil thermostat just likw the coolant doesn't flow thru the radiator until it is above the temperature determined by the coolant thermostat.

P E H

P.E.Haiges,

But wouldn't you say that if the water isn't very hot, the oil wouldn't be very hot either? Shouldn't there be a correlation between water temperature and oil temperature?

I guess with it being an average of 25-30 degs. during the day, and the rush of wind hitting the lower oil pan, the oil is already kept cool. Well at least I hope that's the situation. I don't recall if my ' 80 SD's oil cooler gets warm or not in this kind of weather. I know that even with all that highway speed in the TD, at idle the oil pressure kept up at 2 bar.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

Sure there is a correlation between the coolant and oil temp. But as Rickjordan says, the oil in the pan on a cold day may take a lot more time to warm up than the coolant which is surrounding the cylinders and in the head where it designed to absorb the heat of combustion.

I think the gist of the answer is that there are 2 thermostats, one for oil and one for coolant and that they work independent of each other.

P E H