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Old 01-11-2004, 07:06 PM
JHZR2's Avatar
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Location: New Jersey
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Diesel temp normal but engine too cool?

Hi,

I have had a number of odd phenomena, which really showed themselves this weekend on my trip from near NYC to Pittcburgh (had great seats for a penguins game)

Start a month back... I was tinkering under the hood, and opened the coolant reservoir cap. for whatever stupid reason, I didnt reclose the cap, it was just laid on the reservoir. I drove (just about all interstate) for over a week, and temps always were OK and heat worked, etc. Didnt loose a drop of coolant either. (temps outside were neart freezing).

This weekend, driving out to pittsburgh, it was lower than 20 degrees at a rest stop on the PA tpk where I stopped. I popped the hood to look around to see how hot the radiator and oil cooler got in these situations. The radiator was slightly warm, as was the valve cover. Definitely not as warm as usual though. Then I felt the oil cooler. It was absolutely cold! As cold as the sheetmetal of my car!

Driving on the way back, I noted that any change turning the heat up, would result in engine temp dropping... OK, thats fine. However, what I didnt expect was that when I turned it down, the temperature would go from its usual point of 82 up to 86-90. I know this is still OK, but it never does this with the heat on between 22-26 and warmer temperatures outside.

-Is it odd that I could drive 100% fine, and even have normal power and economy with the radiator cap not even slightly screwed on?

-Is it odd that after 200mi at 70+ mph, thje oil cooler is absolutely cold, even if it is 20F or so out?

-Is the fact that my cooling system temperatures are fluctating so in dicate that perhaps my system was cooling too well? Or perhaps that the thermostat isnt working correctly?

I am taking my car in for some suspension service to an MB indy on tuesday. If there is a possibility of something else wrong, Id like to have it looked at as well while Im in, not have something that I might catch early come to kick me when the summer comes... Thats why any help or info from this forum would be really great.
Thanks,

JMH

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)
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  #2  
Old 01-11-2004, 07:14 PM
BoostnBenz's Avatar
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Join Date: Aug 2002
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There is always a possibility but here is what I think....

The oil cooler never got hot because it wasn't needed, there is an oil thermostat which decides when for it to open up perhaps since it is so cold outside it was never needed. If it were the middle of the summer and it didn't open up I'd be concerned but otherwise I wouldn't think about it.

As for the temperatures running higher I would guess that since the cap has been off that perhaps some of the water has came out (but the water bottle generally doesn't get very hot), or that since the system isn't under pressure like it should be it is running a little warmer (much more likely). Get a new cap and if it still is acting up then it is time to start thinking about it....
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  #3  
Old 01-11-2004, 07:37 PM
JHZR2's Avatar
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Thanks for the quick reply... I should clarify...

The cap issue was a month back. I fixed it by putting the cap on tightly as it should be, as soon as I noticed. I have driven for about a month (1600+ mi) since, with no problems, fine engine temp that stays consistent, and the water level is always at the right height. The cap was new last summer, so Im pretty sure its OK... Im more concerned with the thermostat.

Ill check the cap, but since in warmer temperatures it was always fine, and consistent, regardless of the cabin temperature setting change, I have to wonder beyond a cap/pressure issue.

Good point about the oil cooler thermostat. My one worry is then that: can we safely assume that even in high speed driving in temperatures in the teens and below, the oil is getting up to a proper temperature to safely protect the engine?
I worry, because a lot of the antiwear additives and oil properties depend upon a proper operating temperature, and I would assume that the oil temp thermostat is set to the middle or upper area of the 'OK oil temp range)/

Thanks for your help,

JMH
__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)
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  #4  
Old 01-11-2004, 08:13 PM
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Join Date: Dec 2001
Location: Chicago area
Posts: 242
The oil cooler is simply bypassed when not needed. Your oil is getting to where its supposed to be and getting there at the right temp. I took a 300 mile trip yesterday and the outside temp never got above 18. My engine also felt warm but not hot. I'd keep an eye on your temp gage for a while but I don't think you have a real problem.

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1985 300SD 215,000 miles
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