My subject is a 91 300 D 2.5 turbo.

The white plastic expansion (overflow) tank developes pressure - is this normal?

I'm loosing water without any obvious signs of a leak anywhere. I loose about a quart every 250 miles or so. No leaks are apparent. No sign of hydrocarbons in the water, fortunately.



Dino

Assuming that the expansion tank you speak of, has a radiator cap, then it would become pressurized once the coolant is warm/hot enough.

Check the radiator cap - Is the seal still good? What about the spring?
Also, check the seating area of the cap - if crud builds up, you loose your seal.

I'm pretty much out of ideas after that, except using your nose to sniff out any possible leaks. Before, and after you have warmed it up/ have pressure in the sys.

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09 Jetta TDI
1985 300D

[QUOTE=Larry Delor]Assuming that the expansion tank you speak of, has a radiator cap, then it would become pressurized once the coolant is warm/hot enough.QUOTE]

Pressure in the expansion tank is normal when warmed up. Is there pressure in the tank in the morning when cold? If you are loosing coolant and there is none on the ground there can only be one explanation.... You have a headgasket leak. RT

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84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

I'm sorting out a slow, not so obvious, leak too. Little experience except with obvious leaks on other vehicles. But I've found some threads on this forum regarding condensation on the inside of a windshield indicating the heater core (inside the car) could have leak. Just food for thought -- barely know our SD let alone your newer model.

Yeah, I lose coolant and there is none on the ground.
But I have a tiny intermittent leak I just discovered.
Took me a while to find it....
Hose at thermo housing.
And the servo I just bypassed leaked a little.
Never enough to drip noticeably. Very slow...
Don't assume the worst.

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300CD '80 (now gone but not forgotten...)

Auxillary water pump? I don't know if this model has it but mine is leaking. Didn't know where it was loosing coolant because it would loose it at idle.