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MJ · Joined: 21 Oct 2001 Posts: 211 Location: CT

When car is cold in the morning the coolant level is a little below the expansion tank line. After driving the car all day and the car is hot I noticed the coolant is much higher when its warm than cold, Is that normal? Once car sits over night it seems lower or is it a pressure issue as I have noticed some leakage at the overflow pipe only after its sits at night. I did have a new thermostat put in and thats when all of this started. also I guess the clamp was loose on the pipe that goes to the radiator which was replaced but I still see seepage a bit only when car sits overnight. So its either the little overflow hose clamp was not tight enough or something else. Main question I guess is does the expansion tank levels change when car is hot and cold??? Why would it seep when car is in the garage and sitting overnight and not while driving.

geminiys · Joined: 13 Oct 2004 Posts: 182 Location: SF, California

It is very normal for the level to rise when hot due to expansion.
The seepage occurs due to rubber hose and plastic housing expansion/contraction ratio. The hose is most likely old and lost its flexibility over the years. Thus, not providing enough of the contraction when everything cools down, leaving a passage for coolant to escape. Another possibility as you have mentioned the clamp been loose.

MJ · Joined: 21 Oct 2001 Posts: 211 Location: CT

Can I replace a section of the hose if needed but will all the coolant come out. Your response was perfect. Guess I'll just keep an eye on it. Can it burst or just leak slowly. Its weird because it only leaks when car is off and it sits overnight and times it does not leak, lately its been slowing down. sometimes not at all. Its weird but thanks

Its an old BMW 1997 328i 200,000 miles

geminiys · Joined: 13 Oct 2004 Posts: 182 Location: SF, California

The small diameter hose that goes from the right side of the radiator nipple to the expansion tank only in use when coolant expands and excessive amount is routed back to the expansion tank. Therefore, if the engine is cold it is safe to replace the hose without loosing any coolant at all. You will need to bleed the system after you are done. I would use a different type of clamp if you still have original in, I did.
A temporary remedy is just to replace the clamp but don't over-tighten it as you will have the radiator's nipple smashed and leading to more expansive repair. Keep your eyes on the bigger pipe underneath the small one on the radiator's right side, as the neck know to break off completely unexpectedly due to age.