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  #1  
Old 01-08-2016, 02:14 PM
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84 300td oil cooler not warming up

After about 20 minutes of highway driving my oil cooler was stone cold, so on the way back I beat on it a little bit doing some wide open throttle pulls, pulled over as soon as I got off the freeway... Oil cooler still stone cold. The bottom line is very slightly warm, top line stone cold. Both oil cooler end tanks stone cold.

The ambient temp today is around 30, so not very warm but I'd expect some warmth in the cooler, I'd especially expect the supply line (I'm guessing it's the bottom one) to be pretty hot.

Do I have a stuck thermostat or does it take some serious heat to get these to flow?
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Old 01-08-2016, 02:41 PM
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The problem is usually the other way - the thermostat is stuck open allowing the cooler to keep the engine oil too cool. With temps in the 30s I doubt seriously whether the thermostat would open on a properly operating system. Check again when temps get up to 80 or so, that would be a better indicator...at least that would be my opinion.
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Old 01-08-2016, 02:46 PM
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Outside temp doesn't really have THAT much to do with it, I got the coolant temp to come up a few degrees after some full throttle driving. Even if there was a little bit of flow into the cooler the bottom line would be hot, I'd think.
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Old 01-08-2016, 02:50 PM
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And it's definitely not stuck open, there's no way the cooler would be cold with cold supply and return lines if it was open...

Sooo.... What part actually fails that I need to order? The dealer just has a bunch of parts, not one unified "this is the oil cooler thermostat" part.
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Last edited by chrisgt; 01-08-2016 at 03:22 PM.
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Old 01-08-2016, 05:21 PM
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Well I always laugh at people who shotgun parts at their car without doing some diagnostics... So I went out and drove like a madman for 20 minutes, pulled over and stuffed one of my thermocouple probes in the dipstick hole. Result? Oil at 202 degrees. FSM says there should be heat in the oil cooler at 95 +/- 4 degrees, 202 is only 94 degrees, so I guess it's within the margin of the thermostat not opening. Living in the city makes it difficult, next time I'm on back roads where there are steep inclines for a mile maybe I'll be able to push the temp well enough above 95 degrees to get some sort of accurate diagnostics.
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Old 01-08-2016, 05:27 PM
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Here's a thread that has quite a bit of information on the oil cooler thermostat including pictures that will help you figure out what, if anything, you might need - Oil Cooler Thermostat Replacement
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Old 01-08-2016, 09:22 PM
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Ahhhhh so I have a 110 degree thermostat probably. I wonder why everything I found said 95c except for that thread. Well then, had I found that right away I wouldn't have worried so much.

Random sidenote... When I first got my car it was blowing oil EVERYWHERE in the engine bay, the air cleaner wasn't assembled properly. I put it together properly on the side of the road and we drove easier on it the rest of the trip with no issues.... It was a really hot afternoon (Bought the car in Virginia), I wonder if that's the only time it's ever opened, and it sprays oil when it does.... I guess I won't find out until like July when it gets above freezing up here
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