Replaced original Tstat and have same result as others
 

My car used to run at a tad over 80c . After having a overheating issue I replaced my faulty Tstat with one from Autozone. I'm getting the same results as others. It runs consistently at 100c now.

After reading 2 good threads I realize it must be the brand. The original was a wahler Tstat.

Is it worth buying a new OEM Tstat ?

Also where can I buy an OEM Tstat?

Get one from Phil. Get a 79C t-stat. DON'T use any autozone junk on a MB.

Fix your overheating issue first.

I'd just buy one from the MB dealer in your neighborhood...

Not THAT expensive...

:)

karugs if it was running at 80C steady before he replaced the t-stat then it must be a bad t-stat that he bought, not a problem with the car.

He had an overheating issue prior to replacing the thermostat...

Sorry I missed that sentance. I stand corrected.

Autozone sometimes sells Walher T-stats, sometimes the Duralast brand, sometimes Behr. You have to know which one you got. I think I have a Behr on mine, been a long time since I replaced it.

If that was what's causing the overheating issue then get the right one. When my T-stat got stuck open I would cruise close to 100C on the highway, which was weird because of the added air flow that should reduce the operating temp. Now without any accessories on my gauge reads a hair below 80C which is VERY surprising, as before it would usually be a hair over 80C. I've never replaced the T-stat between those times.

Who is Phil?

typo
 

Go to the top of this page and click "BUY PARTS" then "FASTLANE". You'll see Phil's phone number. Without them, this forum would not exist. Support the forum and buy from Fastlane.

Thanks!

There are 2 choices Behr or Germany I'm not sure which one to buy.


The amount of threads dealing with issues with Tstat replacements is amazing. All of the replacement Tstats seem to run at about 100c or higher . It really is insane.

There should be a sticky on some threads dealing with this situation. People are buying various other parts in hopes of fixing the car from running at 100c or higher.

http://www.peachparts.com/shopforum/diesel-discussion/193569-troubleshoot-617-952-cooling-system-84-300td-turbo.html

http://www.peachparts.com/shopforum/diesel-discussion/213203-stant-thermostats-temperature-regulation-101-a.html

If your car is consistently running at that temperature, it is not the T stat!

Plus, they almost always fail in the open position, not closed.

Fix the problem right instead of throwing T stat after T stat at it.

Have you done a citric acid flush?
Are you running the correct coolant?
How old is the radiator?
Is the fan clutch nice and tight when hot, or is it getting loose?
Water pump leaking (unlikely)?
Expansion tank cap creating a good seal?

My car never runs hot. Only after changing the old Tstat has it been running like this.

I have flushed the rad in July. I use the G-05 fluid. The fan clutch is perfect. I have no leaks in my system.

When you replaced the thermostat, did you remove the upper radiator hose and completely fill the head with coolant?

You also ought to run it unpressurized for a couple of days (cap set at first detent) so any air bubbles can purge themselves. If you fill it and run it with the cap closed it can become airbound because the bubbles expand when heated and can't move.

FSM says the system is self purging/ bleeding.

"The thermostat housing has an automatic venting
system."

I will try to unscrew the cap and put it on the first detent.

I am running cool since tearing the engine open, it is effecting efficiency. I used what I thought to be a nice looking t-stat. It was a Behr, 87*, and may have been from a 240d.

I thought normal t-stat failure resulted in overheating, not underheating.

for reference: the coils face the block.. correct?

No, it can fail in the open or closed position.

Yes.

There is a small hole in the edge of the T-Stat with a little rivet looking valve in it. That is part of the venting/bypass system and there is an arrow on the body which is supposed to be pointing up when the t-stat is installed (assuming it is vertically oriented). Some aftermarket t-stats don't have the hole and sometimes people don't install them facing up which can have an effect on the self-purging system.

This is one of the things a lot of people miss but makes the biggest difference. I never change the stat on any car with out doing this. The stat will not open until it senses hot water and if you do not have water in the head for it to sense it will never open. Also as others have stated you must install the stat with the bleed hole on top.
One question; do you know what temperature rating the new stat is?

80*c

I know you might cringe, but I squeeze the top radiator hose, then plug the little line going to the top of the expansion tank and then release the upper hose, and repeat. this usually sucks in a bit of antifreeze from the expansion tank.

Interesting idea, I'll have to try that some day.

Thanks for the tip. I had the same problem. After changing t-stat, waterpump, flushing radiator and refilling with G-05, temp gauge was at 100 C. Loosened cap on coolant reservoir to first detent and drove for ten minutes. Must have been trapped air. Gauge now reads between 80 and 90. Easiest fix yet.

Thanks again.

Glad to have been of assistance.