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W123 300D thermostat problem

10K views 14 replies 11 participants last post by  andros87 
#1 ·
Gents,
Recently purchased W123 300D (1980 - South Africa) had to overhaul the engine.
Now, I have a problem with the thermostat.
Tried to install two (brand new ones) and it does not seem that they are opening at all. Drilled few extra wholes through both just to increase water flow, but to no avail.
(By the way what is a correct thermostat temperature for 300D?)

Now I am driving without a thermostat, temp sits on 40°C (I am aware that it is not good!).
What am I doing wrong? Any suggestions?

Thank you in advance,

Tony
 
#2 ·
When the thermostat opens, the front disk opens and the back disk closes, shifting flow from recirculating back into the engine to flowing through the radiator. Removing the thermostat removes that redirection function and allows most of the flow to go back into the engine and not the radiator, which means little, if any, cooling.

I usually test a thermostat by putting it in boiling water and watching it respond. I'll also place a thermometer in the pan of water, heat it, and see at what temperature the thermostat opens.
 
#4 ·
Agree with ndcv, those are new ones and the chances of both of them not working is very small. I'd look somewhere else. You may want to describe how your car runs. That way it would be easier to diagnose.

Or perhaps the temperature sensor itself is going bad.

Just my 2 cents
 
#5 ·
Gents,

Thank you for your replies so far, still running without the thermostat.
When you put in the thermostat, the top pipe leading to the radiator gets extremely hard, and water starts leaking on the pressure cap outflow pipe at the radiator.
Not a lot of water, but just enough to make you nervous that pipe is going to rapture. (Brand new pipe)
Is there a blockage of water flow somewhere around head or must just replace the pressure cap on the radiator?

As I said, engine has been overhauled, head re-tightened after 1500km, and it runs smooth.

The only thing that puzzles me, exhaust is relatively black and when you press the pedal (any speed), darkish smoke comes out. Is the mixture (let me use gasoline engine terms - since not very familiar how the high pressure pump works) too rich. Should I go for tuning??

Thank you for your valuable input so far,

Regards,

Tony
 
#6 ·
not to be a wise guy, but are you sure you are putting in the t-stat the correct way? ie. not backwards?
on another note even brand new t-stats are known to come out of the box bad. test it in a pan of water.
 
#9 ·
You can check the t'stat by putting it in a pot of water on the stove top with a thermometer.

An 80 C t'stat will begin to open at 80 C and be fully open at 94 C.

Not sure which version you have, see the attachments.
 

Attachments

#10 ·
What you are describing as a problem is perfectly normal. The water in the radiator should be at the upper sign inside the radiator. There is like a plastic ending of the radiator gauge, which does not do anything, and you can see it through the filling hole.
Now as the engine heats it is normal that some water will get out from there because the radiator cap has a pressure relief valve. The radiator hose its also normal to stiffen up at 60 - 80 degrees Celsius. The water circuit has a working pressure of about 2 BAR as far as I know.
By the way you have an European model or US one?
The black smoke you should analyze only after your engine is warmed up at 80 degrees Celsius.
If there is still black smoke, then it might be an engine advance problem. 24-26 Degrees before OT. Reset the IP.
I guess your injectors are ok....
 
#11 ·
w123 300d - 1985

hi guys i have 1 w123 300d of 1985 and i intalled a new thermostat but doesn't open. itried it in a bowl of hot water and it was openning in under the 90 degrees. the thermostat must open in 80degrees. When i install it on the car, the temperature of the car is going almost at 100 degrees and the thermostat is still closed. does anybody know why this happens?
 
#12 ·
Andros,

In the future, start a new thread when you have a question instead of posting in an old thread. Just FYI, it makes it easier to figure out what the question is and you'll get more attention for your post, which is your goal!

The thermostat might be installed backwards. There is a right way and wrong way to face the thermostat when you install it.
 
#14 ·
op im sorry im new on the website and i dont know very well how to use it! thnx for info about aite uberwasser. mow the thermostat i think cannot be installed backwards. Its probably broken as justpassinthrou wrote. i bought it from cyprus mb dealer 2 weeks ago brand new one. I will take it back and i will ask them to give me another one
 
#15 ·
fan clutch

guys i think the problem with thermostats is the visco fan clutch. Propably there excist 2 types of visco fan. suchs and behr. behr is the original and suchs is simillar pattent. the different between these 2 types is that suchs is always locked and cooling all the time the water inside radiater and behr is not always lock so allows water to get a a little bit hot in the radiater so the thermostat accept the little bit hot water and opens. please check this out and comfirm me if im right because i believe this is the problem. i checked everything on my car and i check the thermostat in a hot watered bowl and it opens. on the car doesnt open when the engine is on. if the engine is off and the water gets hot from the temperature of the engine opens.
 
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