Hi folks:
I have a problem with 1985 300DT. What is the normal time for warm up on this car? Well its about 20F here in NY, and it takes about 15 minutes of idling and about the same time of driving, before the temp shows 45 C (The needle just moves at this point above the 40C). The gauge I know is fine. I touched the top radiator hose and its just luke warm even after about 30 minutes of driving or idling. All was fine last summer. No over heating at all. Now its very cold in Ny and the problem is under heating and as a result the hot air is at best luke warm.
Monovalve is new, water recirculation pump is fine.

Could it be the thermostat stuck in open position. If so How can I diagnose it without taking it out?

Whats the normal time for engine to reach 80C in NY like cold of 20F ?
And If I must replace the thermostat should I get one from dealer? I just want the best as I have heard the horror stories with after market and Autozones etc.

Thanks

MVK

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One penny saved is three penny earned.

1985 300D Turbo 179,000miles

Is the car even reaching 80 degrees celsius after prolonged driving? If not, you have a bad thermostat.

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Regards,
Aaron

Bad Thermostat!! I have had good luck with Robertshaw brand thermostats in other vehicles but I don't know if the make one for MB's. RT

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When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

BEHR makes the thermostats for Mercedes-Benz.

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Regards,
Aaron

Thanks for the reply.

The car reaches about 60C after a long long drive but not above that. In summer it reahes about 80-90C. And never over heating. I suspect a stuck open thermostst that must have gone bad just this winter!!!!!

Well whats the normal time to warm up to 870C to 80C once you start in morning if weather is 20F?
If someone can tell me this I think I have a value to compare mine with.

If I choose to replace the stat, its going to be one from the dealer.

MVK

__________________
One penny saved is three penny earned.

1985 300D Turbo 179,000miles

Something like five minutes of driving 55 mph.

I only do about one minute of warmup before slowly taking off. A diesel doesn't warm up very much at idle in cold weather - it's just not going to generate heat unless its under load.

You have a classic case of stuck open thermostat.

1982 300D

Ken300D

Yeah my car did that when I had my broken t-stat. It would run warm at times (half open) but also run really cold when it is cold (always half open no matter what)

Still a smart design I think. Kinda funny that ive had people tell me to buy aftermarket 'fail-safe' thermostats when the MB t-stat actually does this by default ..

I replaced my T-Stat with one bought from the MB dealer (Wahler) and the water temp went up close to 100*C before the T-stat opens and after that it was fine.

In Fall (temp in the 60s) the water temp was always at 100C.

so I took that out and put in an Autozone Wahler T-Stat and that one works great!

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2008 BMW 335i Coupe

mvk, had the exact same thing as you, replaced with a bosch t-stat - no problems. it usually takes 10-15 min of in town driving to get to the 80 deg mark.

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

I have only seen the ambient conditions down to around 0 dC so far but first couple miles at around 35 mph and I am at 40 dC at which time the heater starts blowing warm air. The next couple miles at 55 and I am above 80 dC with the heater going pretty well. I don't let it sit there more than a minute or two prior to driving off slowly.

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Jim

Thank you all for the replies. I will definitely replace the Thermostat with a new MB OEM.
MVK

__________________
One penny saved is three penny earned.

1985 300D Turbo 179,000miles

a stuck open thermostat will NOT allow the engine to reach NORMAL operating temperature when the outside ambient temperature is COLD..........in the summer, this becomes a moot point.........however, reaching normal warmup temp will take a little longer..........IF youdo not wish to deal with wrenches etc in the cold> you may get a piece of rubber< thinner the better> and place it twixt the radiator and the condenser to BLOCK cold air, however, this is CHEATING, and still will not allow the car to warm up completely.....you may need to further block the front of the condenser........when the ambient temp increases, you MAY need to OPEN up the airflow to compensate........i did this since the end of last winter and it was ok............last weekend, i finally replaced my LEAKING waterpump and also replaced the thermostat w/ one from autozone (about $15) and the system functions as new.......takes about 5 minutes to FULLY warm up to normal operating temp..............the heater can BURN!...........best wishes always, spo out.

Well I did a bit of more search on the brand of T-stat and almost all of them suggest the Auto zone Wahler over the OEM. So Now a new dilemma. Which one. Now I am more inclined towards the Auto zone brand.

MVK

__________________
One penny saved is three penny earned.

1985 300D Turbo 179,000miles