Hello

What is the normal pressure in the top coolant hose going to the radiator, with the engine running?

My engine, 300D turbo, runs a bit hot (95-100 C) and I'm trying to see if the thermostat would need replacing. Squeezing the hose with engine running and the temp in the 90s I feel no pressure in the hose. I would expect pressure from the water going to the radiator. Any other ways to check for a thermostat malfuntion?

Thanks in advance.

Nicolas

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1982 300D - http://members.xoom.com/nicodore/

When hot the hose should have a tight feeling to it. When cold should have no pressure. Replace the cap first then proceed with other repairs.

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Benzmac:
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Thank you both.

I don't feel anything, not even the sweet little waves of a small spring... Anyway, I'll check the thermostat.

Thanks again

Nicolas

In the top hose there shouldn't be much pressure built up at all. The radiator cap won't allow pressure in the overall cooling loop to exceed about 15 psi (about 1 bar.) If the thermostat is opening, the upper hose should feel hot to the touch.

I suspect your thermostat is opening, if it wasn't the engine would overheat in a short time.

The replacement caps are 1.4 bar. That is = to about 20 or so pounds per square inch...When hot, the hose will be tight and pressurized if all is well.

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Benzmac:
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Well, reading the comments I got a new radiator expansion tank cap yesterday from MB. The old one was really worn out.

No change in hose pressure.

BTW, my main concern is that it seems to be running hot as it is. The temp goes from 95 to 100 C, even on cold days at moderate speeds (no AC, doesn't work...), with plenty of air going through the radiator. It's not much of a concern now, but with winter coming I want to have the engine in as good a shape as possible.

Thanks all for your help.

Nicolas

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1982 300D - http://members.xoom.com/nicodore/