Changed my radiator and thermostat and have since been having a cooling issue. When I have the a/c on, the temp gauge reaches between 100 and 120 degrees, about in the middle. What is the temp the car should be running at? It's hotter than heck out and humid here in Miami. When I removed and re-installed the new themostat (Behr), it came with two rubber gaskets. I only used one, the round one with the hole. I couldn't figure out what the other one was for because I didn't have to remove one. Don't know if that has anything to do with it. Also, I have opened the reservoir a couple times and air has been coming out. The last time I opened it, I couldn't hear any air popping out.

When I changed the radiator, I did not flush the block and there are tiny pieces of orange floating in the reservoir. Is there a problem with the thermostat or could it be the water pump? I'm not a mechanic and don't understand how everything interacts. I am planning on having the whole system flushed but am wondering what the issue is.

Where would you recommend I start, if anywhere? I think that is too hot for a motor to be running regularly. I probably shouldn't have replaced the thermostat. If it ain't broken, don't fix it! Thanks, Lance

That does sound too hot, my 300D (with a new radiator stays between 85-95C in 90-100F temperatures with the AC running. It will only reach 100+C if I climb a very long steep hill at highway speeds, then it cools down immediately on the downhill drive.

I don't know what the "tiny pieces of orange" are but it does sound like you need a cooling system flush. You may also have some air trapped in the system. Some times disconnecting the upper radiator hose and filling through there helps. Also, try running the heat for a little while to remove any air from the heater core. It will probably be easier to flush it first, them worry about the air when you refill the system. Don't worry about the "extra" gasket, it's probably for another application. If none of this helps, you can try reinstalling the old thermostat.

run car @ 2000 rpms with defrost heat on high until you see a dramatic reduction in temp reading should just take a few minutes, to bleed air out of system. if it got up around 120 i would be getting cautious. this is per mercedes mechanic who has all the certificates and he said this is what is recommended

i had replaced a bunch of parts and found out it was a bad temp gauge.

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Brian

82 300d turbo 164k - passed on
83 sd - passed on
04 civic hybrid - DD
06 GTO for sale - passed on
84 VW Rabbit Diesel 4dr.- passed on
94 S350D - DD
94 S320 - soon to be DD

Will try the heater and adding through the upper hose. When I removed the old t-stat, it was a bit rusty in there or the water was a bit on the orange/rusty side. Of course, I threw out the old t-stat and garbage was picked up today. I will let you know if those things change the situation. I know some guy suggested that I boil the t-stat first to make sure it functioned properly and I didn't do that. Don't know if that's it or not, but will try this other stuff first and post results. Thanks! Lance

Well, if the coolant looked rusty that's an indication you should flush the system too. I'm assuming you gauge was reading OK before? BTW, did you install an OEM thermostat?

The gauge was reading fine before. And the thermostat was a Behr, exactly like the one I replaced. I just spoke to my neighbor who said it was unnecessary to replace that part. Who knew?

After having been home for about an hour and a half, 2 hours, I opened the reservoir again and more air came out, like opening a soda.

Where is this air going to escape from if I leave the reservoir cap on?

The reservoir is the high point of the system and should be half full of air, when the engine heats up the air should be pressurized up to the pressure rating of the cap. If there is excess air in the system it should eventually find it's way to the reservoir, resulting in a lower level. If the system stays pressurized overnight, you need to start considering a head gasket problem.

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Just out of curiosity, what were your temps before you did the work?

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1981 240d
Newport,RI

Lance,

Those temps are too hot.

Based on the work you did to the car, there are only two (maybe 3) possibilities: 1) air bubbles trapped in the system or 2) a bad thermostat. Also, did you make sure that the arrow on the new thermostat was pointing up?

I am assuming that your temp readings were around 90 C before the work you did. (please confirm).

As per the FSM: run the system at intermittent operation (with the heater on defrost the whole time) from a cold start up to ~60 C with the radiator cap off. Then put the cap on. It is a self burping system and should require no special manipulation to get air bubbles out.

The orange bits are probably rust, and it would suggest a full coolant flush and descale-ing.

The extra o-ring (the smaller one) that came with the behr t-stat was for use in a different car.

I know it seems crazy that a new thermostat would be defective, but it is alarmingly common. I recently went through the entire cooling system on my 84 300TD trying to track down the source of my 100 C operating temp and it turned out to be the new t-stat (ironically the one that was in the car when I bought it was the same way). The full story is in this thread: Troubleshoot a 617.952 cooling system (84 300TD turbo)


One more thing, what is the pressure rating on the new expansion tank cap you installed? It should be printed on the cap (e.g. 120).

I turned the defrost/heater on tonight in this Miami heat but didn't drive long enough to tell. Will take her out tomorrow and test. On the thermostat, I think there is only one way it will go in. The end of the tstat that protrudes went towards the block with the hole on the tstat pointing to northwest or 11:00. Right? And my temp readings did read about 90 and never budged above that before the new rad. change. I will have to check the pressure on the new tank cap in the morning because it's dark out now. I will also take your advice and take the cap off and run the heater/defrost tomorrow to see if that takes the air out. Will post findings tomorrow. Thanks again for your help. In the future, should I guy test the tstat before installing? They look pretty simple and can't believe one would be defective. BTW, the temp gauge, where does it gather that temp from? Is that from the block?

#7 post- http://www.peachparts.com/shopforum/diesel-discussion/121288-bad-thermostat.html#post868343

i would leave the cap on it is a self bleeding system if done properly. no joke high heat coming from defrost keeping a steady 2000 rpm's will bleed your system in minutes, second set of eyes keeping an eye on coolant/water level in case it really burps

__________________
Brian

82 300d turbo 164k - passed on
83 sd - passed on
04 civic hybrid - DD
06 GTO for sale - passed on
84 VW Rabbit Diesel 4dr.- passed on
94 S350D - DD
94 S320 - soon to be DD

If you back fill the system using the "S" shaped heater hose that comes off the L rear of the cylinder head and carries water to the heater manifold, you won't have to burp the system. This way the head is filled first then thru the t'stat and into the radiator with the only air being what is in the heater core (if it was drained). You can drive the car right after filling the cooling system this way and it won't overheat.
When its hot (drive it about 1 mile) you then select defrost and later add any water the heater core took up.

I use a spray nozzle with a shut off handle made for watering the garden, it fits the ID of that hose, you remove the hose end at the manifold on the firewall, not at the head. Leave the filler cap off the expansion tank and when you see it gurgling up you know its about full. I also add antifreeze the same way but stick a funnel in the hose for that purpose.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

I have no idea why the FSM says to leave the filler cap off until around 60 C, but it does.

I highly doubt that the problem is trapped air bubbles, but its the easiest thing to check (and its free). Since the block was never drained when you replaced the radiator, you don't need to worry about the alternative ways to fill the block. And again, the coolant system is a self bleeding system, as per the FSM you can fill it from the filler cap, leave the cap off, turn on the defrost button, run the car at intermittent speeds up to operating temps, recheck the coolant level below 90 C and you're done.

I have drained and refilled the coolant on my 84 300TD turbo probably 8 times this summer while trying to trouble shoot the cooling system. At least 4 times I drained the whole block. No special burping method was ever required (though I tried several).

You got the front to back orientation of the thermostat right (foot plate towards the back of the car) and the o-ring (it really only can go in one way). But there is a small arrow stamped on the main body of the thermostat that should point up, like this :

I don't know why it would possibly matter, but the arrow is there and all the repair manuals mention it.

Lance,

I would bet my eye teeth that its the thermostat. I know, I know. It sounds crazy that some simple little piece of metal could cause so much trouble. Besides, its a brand new OEM part.

I did citric acid flushes, pulled the radiator twice to clean it inside and out, tried 4 different "burping" methods, replaced the radiator, swapped the filler cap, swapped the fan clutch, pulled the waterpump to see if the impeller had worn down, and even tested the thermostat in boiling water by itself and while mounted in the thermostat housing.

It turned out that I had TWO bad thermostats in a row, one that came with the car and one brand new Behr. It wasn't until I swapped out the old one from my 85 300TD that my temps dropped from 100 C to 90 C. More importantly, the temps on the 85 300TD went from 90 C to 100 C by doing nothing more than installing that same brand new Behr thermostat.

Rant over.

The coolant temp sensor for the gauge is in left side of the block (drivers side) between the glow plugs for cylinder 2 and 3.

Oh yeah, and I pulled the sensor and confirmed the accuracy of my gauge readings by immersing it in hot liquid next to a laboratory thermometer, during my saga to trouble shoot.

Craig, How can you tell if it has a head gasket issue? After the radiator broke, I did get some steam but turned off the a/c and pulled over ASAP. I was able to reclamp to the old radiator and fill with water and the temp was perfectly fine after that. It did run hot for a few minutes, though. I had a busted head gasket on a '95 E320 I had but that was a very dramatic event.