Replaced T-Stat Engine now getting real hot - PeachParts Mercedes-Benz Forum

Capt Kirk · #1 12-19-2001, 09:59 PM

On my 1982 300D I recently replaced the Thermostat (On Saturday the 15th) because the old one was stuck open. I knew this because on my trip out to Ft Worth during the day time the temp would sit at 80C and fall to 60C when the sun went down, also the heater wasn't very warm. I was driving at a very nice clip so having the temp under 80C was kinda a dead give away.

Anyways, when I was in the garage replacing the thermostat I drained the radiator of it's fluid and proceded to remove the old thermostat and put the new one in. I didn't have a single problem and I put the T-stat in the right direction (not sure if it could go in backwards). I then put it all back together and filled the resevoir back up with new Antifreeze while letting the engine idle with the heater on. It took about 5-10 minutes for it to get to 80C when the temp dropped back down to about 60 (cause of the cold coolant getting into the Engine). After it got back up to 80 I decided to take it for a little spin to see how it did with air flowing through the radiator. After 5 minutes the temp jumped to 100. Since I never saw this sort of behavior from my temp gauge I desided that I'd better stop my test and let some air work it's way out of the system.

Now we jump to today (the 19th). The temp is doing a lot better then on Saturday. Instead of jumping to 100C after a few minutes it works its way slowly to 80 then a little quicker to 85-90 and then hops between 100-95C (with the Heater on the whole time). I don't dare turn the heater off.

I know that this is way to high especially since it's only 65F outside. Could it be that the temp gauge is wrong?
I don't think there's any large amount of air in the system because the water level hasn't been going down the last 2 days when I checked it in the morning (I drive it 20 miles everyday at least, so its safe to assume the bubbles have worked themselves out.) I also know that the themostat is of the 80C variety and it's from the local MB dealer (has the star on it and all).

Any insight would help. It's very disconcerning when the temp is just sitting at ~100C.

Robert W. Roe · #2 12-19-2001, 11:59 PM

It almost sounds like we have similar problems. I never got over 60 deg C unless I drove at least 8 miles. I got under 15 mpg on one tankful of diesel. My mechanic changed the thermostat, and now I run about 85-95 deg C. My AC also quit late in the summer, but during the summer I'd seen 110-115 deg climbing a mountain with a full load with the AC running. 100-105 was a typical temperature with the AC on. I've been told I'm probably looking at a radiator, but now I'm not so sure that it might not be a thermostat. I still have 85-90 deg running temps, so my problem isn't fixed yet either.

#3 12-20-2001, 01:35 AM

Hi all.
I am very new to these things(about 1 week) but if it helps here is my T-stat running too cool saga. My 300d was running around 60 deg C, and after some time on the highway it would creep up to 80. I changed the T-stat today-removed the old one, put new in and topped off fluid, all seems well in the short time I've driven, runs between 80-85. One thing I noticed is there was a bunch of crap around the inside edges of the housing white crusty stuff might have been from PO using nondistilled water, perhaps just age? I would guess that most of these old MB's could use a coolant flush. On a curious note I didnt test the new T-stat, and the old came out closed which surprised me so I tested the old T-stat by boiling it and while unscientific(I didnt suspend it just laid it on the bottom of the pan) the old one appeared to work fine.
Gregg

Ken300D · #4 12-20-2001, 03:45 AM

While the odds are sorta against it, I have gotten thermostats that were bad right from the start. Several that were not opening at the right temperature, and one that was "sticky" in that it wouldn't open up initially until the motor got real hot.

If you are using a generic replacement, how about trying an OEM (German) part?

Ken300D

Capt Kirk · #5 12-20-2001, 08:51 AM

I only use OEM parts.

It gets some what expensive, but I figure in the long run it's better.

Tom Sweeney · #6 12-20-2001, 10:24 AM

Have you checked the clutch fan? My SDL exhibited similar symptoms. I called to get a thermostat and the mechanic suggested that I check the clutch fan. He suggested that I run the car, after it warmed up, shut it down and count the number of revolutions that the fan makes after the motor stops. My fan kept on spinning after it was shut down. I replaced the clutch fan, that's a different story, and the temperature remains between 80 and 100 depending on the driving conditions.
Hope this might help.

Tom

#7 12-21-2001, 05:55 PM

I realize we are talking about MB's here and NOT Vw's , but here is a little VW trick I always use that may work on the MB too. Due to the placement of a VW stat. it is real easy to get a small air bubble in the system that will not go away, especially on the Vanagons! Those animals require a lot of frogging around ( first lift the front abd then the rear and then the front again) to get the system to "burp" out that little bubble. However, on the Rabbits and Jetta's I have been drilling a very small ( 1/8") hole in the thermostat, a bleeder hole if you will, in the outer rim. ( the part that looks like a sombrero rim) It also helps to fill from the top hose so that there is coolant on top of the t-stat from the beginning. This will be a bit of a mess unless you are quick to put the hose back on the radiator!!

I changed the stat. in my 300D last week and I didn't even drain the coolant, lost about a cup at the most. I like the location on the Mercedes much better than the VW's! ( on top of the engine vs. UNDER the radiator!

be459 · #8 12-21-2001, 08:39 PM

Quote:

Originally posted by Tom Sweeney
Have you checked the clutch fan? My SDL exhibited similar symptoms. I called to get a thermostat and the mechanic suggested that I check the clutch fan. He suggested that I run the car, after it warmed up, shut it down and count the number of revolutions that the fan makes after the motor stops. My fan kept on spinning after it was shut down. I replaced the clutch fan, that's a different story, and the temperature remains between 80 and 100 depending on the driving conditions.
Hope this might help.

Tom

Tom,

Your mechanic was wrong about the way to check MB's fan clutch. That clutch is set to start engaging when the clutch reaches about 95 degree. The only reliable way to test it is to run the engine until very hot so that the clutch can be at 95 degree and you can hear the increasing fan noise which sounds like starting a jet engine.

On the 617 engine, sometimes it is hard to get rid of the air trapped inside.

David

can-do · #9 12-21-2001, 09:55 PM

Greetings Capt. Kirk,

If you have changed your coolant and thermostat and it's running around 85-90 degrees C than I'd say it's probably normal. The engine temp will fluctuate somewhat while operating loads increase or decrease, hill climbing, excessive speed etc. If you have the older model Benz there is a coolant bleed screw on top of the thermostat housing for air bleeding, and on the reservoir models you leave the cap off the reservoir while running the engine to operating temps with heater on full and keep the tank to it's fill line. I don't think i would be overly concerned if the temp came up to 100 degrees C and then dropped down to a steady 85-90 degree C operating temp on the straight aways. If you get climbing temps out of this range I would consider a radiator citrus cleaner for your core.

Charles

Capt Kirk · #10 12-21-2001, 10:03 PM

I'm in North-East Texas, the biggest hill we have is the freeway overpasses

It goes up to 100 and sits there. I'm thinking after Christmas I'll go get the radiator cleaned out, that seems to be the next logical step in my troubleshooting. (This weekend I'm going to take the thermostat out and test it to make sure it's opening at the right temp)

#11 12-22-2001, 04:51 AM

Hey guys and gals,

I too suffer from a benz that runs at 100 but no higher. I have a new radiator and thermostat. I liked it better when it ran at 85 with the old radiator but the new one is in and 100 wont kill it. My mechanic put in an aftermarket radiator which he said was good so I listened to him. I would have preferred oem but at the time I allowed him to make the executive decision. He is the shop foreman for the local MB dealer so I trust him. The primary solution to your problem is most likely the radiator. If your radiator is old remove it from the car and pressure wash it to clean all the fins off. You will be amazed at the improvement in the cooling powers of the car after that. But if it still stays at 100 after that I would feel confident that no detremental effect will be suffered by your car. It is not in danger of over heating at that temp.

PS. I just put in a new thermostat and am getting the same results as you. I will probably drill a small hole in the thermostat to promote evacuation of air. The take home message is dont worry clean your radiator and be happy

good luck

bob

Capt Kirk · #12 12-27-2001, 04:35 PM

Looks like the radiator is at fault. I took it over to a mechanic to look it over (he's a certified MB mechanic, has a lot of old ones out front, he knows what he's doing).

He drove it around for a while to see what it was doing. He confirmed that the current temp wasn't right and that the radiator is the problem because half of it is still cold, even after running for a while.

So I ordered a new Behr Radiator from Fastlane, it should be here tomorrow.

Capt Kirk · #13 12-28-2001, 12:07 PM

Overnight Delivery is one of mans greatest inventions.

My Radiator was on my doorstep before I was even awake

Hopefully it'll solve my overheating problem. I'll see after I get it in today.

can-do · #14 12-28-2001, 07:55 PM

Greetings Capt. Kirk,

It's a great luxury service, but it too has a high price, doesn't it?

Charles

Capt Kirk · #15 12-28-2001, 09:14 PM

heh, the radiator is pretty light so shipping was only $20 for over night delivery. That also was only $10 more then ground shipping, I figured it was worth it.

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