remove thermostat when flushing w123 diesel cooling system

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george - 04 Aug 2005 18:28 GMT

I don't know if I am reading the MB manuals correctly, but it seems to
me that in the topic (20-015) on cleaning the cooling system (deoiling
and decalcification/derusting) they say to remove the thermostat when
performing this. Is that correct? What is the reason? I can't imagine
the t-stat being damaged by a bit of cleaner. If it is neccessary to
remove the thermostat then what do you do--reassemble its housing
without it before doing the flushing? I am assuming you have to leave
the seal in?

Oh, and what kind of place sells citric acid? (for the decalcification)

This is all for a 1980 300 non-turbo diesel (W123 with a 617.912
engine).

George

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Tiger - 04 Aug 2005 21:00 GMT

Calcification is pretty rare if the coolant is MB coolant and regularly
changed... Pep Boys and alike should have citric acid cooling system flush.

Thermostat removal is a must or whatever you pour into the cooling system
will not circulate to the radiator... only the engine if it ever gets
there... so by removing the thermostat, you allow the whole system to
circulate regarless of engine temperature.

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Wan-ning Tan - 05 Aug 2005 04:58 GMT

Ditto (for the t-stat removal).

Whether the seal is put on during flushing does not make much
difference. The seal isn't very tight without t-stat anyway. Also,
flushing is only a short period. There will be some dripping.

If I remember correctly, the MB manual mentions citric acid for
deoiling. I guess that may be necessary after a head gasket failure. I
have never found any retailer selling citric acid, thought in most cases
it is mentioned in food/grocery/chemical trade so I was a little bit
surprised when I saw MB manual mentioning this. There are some people
selling citric acid on eBay but I am not sure if there are different
grades for food or industry usage.

> Calcification is pretty rare if the coolant is MB coolant and regularly
> changed... Pep Boys and alike should have citric acid cooling system flush.
[quoted text clipped - 3 lines]
> there... so by removing the thermostat, you allow the whole system to
> circulate regarless of engine temperature.

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george - 05 Aug 2005 15:42 GMT

> Calcification is pretty rare if the coolant
> is MB coolant and regularly changed...

the problem is i don't know exactly what's inside--this is a used car
and on top of that i just installed a second-hand radiator. i thought
it can't hurt. i don't really see any signs of calcification but i do
see some rust and the citric acid flush is for derusting, not just
decalcification.

> Thermostat removal is a must or whatever
> you pour into the cooling system
> will not circulate to the radiator...

got it. thanks!

> If I remember correctly, the MB manual mentions
> citric acid for deoiling.

"neutral or mildly alkaline cleaner" for deoiling. "citric, tartaric or
oxalic acid" for decalcification and derusting.

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