Operating temp revisited
 

Good Evening All;

A search of the archives didn't really turn up a definitive answer, so I'm soliciting opinions once again...

1985 300TD Cali-spec w/278K on the clock, 101K on new long block.

The thermostat had stuck open, evidenced by the long time required to get up to temperature. Driving highway speeds (70 - 75) with temps in the 40's - 50's I would never see 80 on the temp gauge. Thermostat replaced yesterday, and this morning driving my commute I saw the gauge running right around 100 (ambient temp of low 70's).

Checked the reservoir before driving home this evening, and it was very low (I had run the heater on the drive down this a.m.). Topped it off w/ Xerox and H2O, and drove it home (~50 miles). Outside temps now low 80's, and the temp gauge hovered around 95 or so (about the needles' width below the 100 mark).

Cause for worry, or am I within a viable operating range?

Need to run 500+ miles to Columbus, OH this weekend, hence the concern.

Thanks in advance,
Dave

It should be at 80 most of the time. Probably the new thermostat's a dud. When I replaced mine it started going all over the place too. I just ignore it but it's never gotten as high as 100 though. It is a range though, perfectly fine til the red mark, I just like a nice big buffer.

typically Ive seen that the needle sits covering the upper circle in the eight of the 80 mark.

traffic with ac in the summer can cause a creep to 100, but that;s it.

My CD runs near 100 C all the time after warming up.

90c until I turn the heater on, then it drops for a while until the uncirculated coolant warms back up.

80* all the time, no matter the weather.

If it never got to 80 without the thermostat, then your system is capable of removing the heat. If it now is at 100, then try another thermostat.

I've had two brand new thermostat's (one from the dealer) go bad within weeks of their installation in the last 6 months.

Winter it hovers near 80*. In the summer doing stop and go I've pushed it to the 90* mark, but that drops as soon as I start moving.

AC is dead on my car. :(

I've been seeing many threads here and on other forums about this 100º issue lately after replacing the thermostat.

I believe there is a run of incorrectly calibrated thermostats that were brought to the market.

Everyone needs to stove pot water test their thermostat before installing it in their car.

Put the thermostat in a pot of water, get an accurate thermometer, put the pot on the stove and bring to boil. Note at what temperature the t-stat opens up and compare it to the spec stamped on the t-stat. If it opens higher then the stamped temp, then it is bad.


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+1 but do a search back to around 2002, I remember the same thing then...

Starting point in heat discussion is always confirming actual temp & comparing with dash gauge. That said, I just bought a infared thermometer from Harbor Freight for use on vehicles where a meat thermometer can't be put directly into the radiator. It's good for measuring what temp the tstat opens & checking for radiator blockages. ~$15

+1 on posts 8 and 10.

Check the thermostat before you put it in the car. After it is in the car "shoot the housing" with an laser infrared thermometer. Mine turned out to be right on the money. 80 to 90 in the middle of summer running the A/C all the time. I've had mine head towards 100 in traffic. But, it never actually made it that far.

The above is all on a properly operating cooling system with a new radiator and fan clutch as of last summer.

Burp the system

not so. the motor can easily register low temps with the thermostat out, due to the way water flows without the thermostat. motor can be very hot, but read low, and have no flow through the heater because of it. you still need to have a good clean radiator that would not have shown up with the thermostat out.
no need to burp with a turbo system. self burping.

Unfortunately, it's not that simple. A properly operating thermostat does not just pop open at the specified temp. It should open gradually as the temp rises above the "spec" temperature. According to the 617.95 engine manual, the thermostat should start opening at 80 degrees and not fully actuate until reaching 94 degrees. Failure to understand that concept would make it likely that a perfectly performing thermostat would be misdiagnosed as faulty.

Additionally, the fact that the bypass is not fully closed below 94 degrees would seem to suggest that 80 degrees is not the target operating temp for the 617 engine.

Tango, what do you mean the turbo engines don`t need to be burped? first I heard they are self burping. this is the first I have read this.
All I have read on the forum is these engines need to be burped.

Is the U-shaped little pipe on the front of the engine the burper?

when I first bought the 85 300D, it didn`t have the U-pipe, and other 85`s I saw at PNP didn`t have them either, yet I saw it on older engines. couldn`t tell you now if it was on NA or turbo engines I saw them.
I have one now on the 85.

Charlie