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

You are correct. I failed to explain further. Thanks in adding that information.



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Charlie, what is this U-shaped pipe you speak of? Got a pic?



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It would appear that you have your wires crossed about who said what.

But even though I didn't say that, I do agree with the gentleman who did. The 617.95 engine has a built-in vent in the thermostat housing which is intended to automatically purge air from the cooling system. In my experience, it seems to work as intended. However, given the relatively small size of the passage, it would be easy to envision a poorly maintained cooling system in which the passage was obstructed and incapable of functioning as designed.

Have you ever wondered about that small hole on one side of the thermostat gasket?

Tango you are right. I was refering to post #13, VSTECH. my appoloizes. :o

I don`t remember a little hole in the thermostat, but been a while since I have one in front of me to look at.
I know Diesel Giant shows drilling a little hole in one for a cooling problem,
but something I wouldn`t do, better to just fix the problem.

DeliveryValve, the little U tube I was refering to, is the one in the front of the head, that connects to the watter pump housing.
I was with JT20 up here in Portland, Or yesterday. looking at his 85 300TD, it also doesn`t have this tube.
http://i131.photobucket.com/albums/p...t/SSPX0407.jpg

Here is picture of what I was talking about. Thanks to SIRNIK84 in his currently running thread.

Charlie

I didn't say the hole was in the thermostat. It's in the thermostat gasket.

http://catalog.peachparts.com/ShopByVehicle.epc?q=1982-Mercedes--Benz-300d-Cooling--System&yearid=1982%40%401982&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6190%3AMBC%7C1504%3AED%7C10 000135%40%40300D&catid=240909%40%40Cooling+System&subcatid=240977@@Thermostat&mode=PA

Ok, now Iam up to speed with you.

Charlie

Ah, I didn't realize not all 617.95x motors had this part. Interesting info.




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Per FSM.


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I have seen that little vent tube before when the hose was off. I wonder if all 617 engines had this, or was started some where in mid production?

Then why does every one say to burp the system? I usually fill the upper hose until I see the coolant come out the radiator, then slip on the hose.

Now I need to check the 240 to see what it has.

Charlie

Chamalu,

I replaced the U shaped tubing on top of the water pump and my understanding it that it is a Pump Vent to make sure the Pump is flooded. My U Tube was dripping. Phil had the tube.

This means it burps the Pump (Primes)but not the block passages. I never heard of "burping the block".

My 1989 325 BMW 325i has a needle valve Burping location on the thermostat housing.

I don't believe these MB have this but if they do it may be on the T Housing.

I'll have to look at mine.

Steve

Great Sketch. That shows it all. TY

BTW,

These U-tubes usually starting dripping in the back where U really can't see where it is cracked or corroded. FYI the tube is made out of steel not a yellow metal as I had thought. My Tube was just worn out from the inside from water flowing through it. I'd call it Erosion Wear. Now I don't use any cooling water at all. Before I had to add some once in a blue moon.

I agree.

from what i have seen, only the '85 / late '84 does not have it.

I had an '81 240d that did have it.

My 80 240 has the metal U-tube. I put one on the 85 a few years ago thinking maybe some one removed it. can`t hurt I guess.
I have a spare 84 engine, I`ll have the check it when I get back home.

Maybe they ran out of them ;).

Charlie