Hi: My mechanic took a look at a heating problem, replaced the faulty monovalve and said I very much needed to flush the coolant and replace the thermostat which was broken. But, for $200 I figure I better do it myself.

I don't want to do the flush myself. I found a place that will do it for cheap. The question is, after they flush, I want to be the one to put in the thermostat so it doesn't go in backwards. Since they've flushed and refilled the coolant (with the mercedes type), I'm wondering how much coolant I'm going to lose unbolting the thermostat cover and putting in the new thermostat? Is it going to be gallons or just a dribble? After I put the new part in, do I just pour some more coolant in the expansion tank to replace what was lost, or is there something else I'd need to do? Many thanks!

What year and model?

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Ron
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It's a 1981 300SD. Thanks.

You will loose some. Make sure the engine is very cool. You can replace what you loose in the overflow tank. If you quickly have a helper hold the hose above the level of the overflow tank you will loose even less. I am not sure if your Tstat will have an arrow on it but if it does point it skywards. Make sure you use new gaskets and dont overtighten, to point of stripping or cracking housing.
Good luck

__________________
Ron
2015 Porsche Cayman - Elizabeth
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace

This is the procedure for the thermostat installation, it shows the correct direction:

http://skinnerbox.steaky.org/Service/W123/w123CD2/Program/Engine/617/20-110.pdf

Post #5 attached picture.

Radiator covering
Radiator covering

You will loose roughly one and a half gallon or less, depending upon how fast you are.
If this is done outside in near zero temperature, you risk frost bite, the coolant will suck heat from your fingers/hands very fast.

Please protect your health...

Antifreeze, Ethylene glycol intoxication, Toxicity, Metabolic Acidosis
http://www.peachparts.com/shopforum/diesel-discussion/139585-antifreeze-ethylene-glycol-intoxication-toxicity-metabolic-acidosis.html#post1037466

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1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

I would get a clean bucket and drain 2 gallons into it before I started any work. Thenyou can reuse it since it'll still be clean.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
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Karrsst,

Drain the radiator. There is a plug in the bottom to drain it. That will be enough that very little coolant will be lost when you R&R the thermostat and when you put the coolant back in, you will put in the correct amount.

P E H

Great tips - great advise! I'm on my way! Thanks again!