Uh oh... Coolant leak. Possibly headgasket

[Dan in NZ]

Drove 300km last week, then the "COOLANT LEVEL" came on. I had topped it up a week before, so was a bit concerned. 600km later, the expansion tank was empty again. Drove another 400km on Sunday, and the tank was empty again.

I took it to the dealer this morning, and they pressurised it, but didn't find any leaks and held the presure. They topped it up again, and I drove about 5 minutes down the road and parked. When I parked, there was a steady drip coming from the expansion tank side of the radiator, but I did't open the hood to see where it was coming from.

So I'm thinking that it only leaks when the engine has been running, with a leaking headgasket that would pressurise the cooling system a lot. Since there were no drips after being pressurised with a tester for 10 minutes, and it only leaks when the engine is running.

Anyone got any ideas???

[Gene in NC]

Similar coolant loss cured by replacing Throttle Housing Heater Plate at 138k on'89 525.

[Dan in NZ]

I have a bit of dried crusty coolant there, but a steady drip coming from the expansion-tank side of the radiator. I'm going to assume it just has the typical bmw leak where the expansion tank joins to the radiator.

[uscharalph]

How much did this replacement cost you?

[Gene in NC]

Failure or leak at throttle housing puts coolant on engine wiring harness to main harness with exposure to corrosion in the contacts. Trust me, you don't want to live through that.

[niall]

just about the headgasket mate,
it doesnt necceserily have to pressureise
the coolant system, if it "burning"
water, put your hand over the tailpipes
and see if you can feel any moisture,
you know what i mean?

[CheapCheap1]

I would do the rad-pressure test to see where is the leak.
Good lucks...

[Gene in NC]

My head gasket leak was hose clamps. Head gasket just replaced by PO. BBUUTT mech reused BMW "one time" hose clamps. Clamps ha appaerntly been reused more than once. Two are leaking. Fix tomorrow.

BMW factory clamps are designed for fast factory assembly, not reuse,

[Peter Mac]

:( :( Dan have same problem on my 1994 525i, leak is intermitant will fill up tank and then it starts to leak, other times its fine,how did you get on with yours.

[liquidtiger720]

are the gaskets on the expansion tank repairable?

[uscharalph]

are the gaskets on the expansion tank repairable?
You can purchase just the expansion tank only, so you must be able to get gaskets

[Peter Mac]

How does one remove the clear plastic expansion tank from the radiator, and were are the seals, are they around the sensor.

[Dan in NZ]

Check carefully where your leak is coming from... I thought my expansion tank was leaking, but it was actually a crack near the bleeder screw, which is part of the black plastic bit. If it is just your seals, I have a pair of expansion tank seals that I didn't use (just got a whole new radiator, about NZD$300).

For a better look, there's a metal plate that surrounds the top of the expansion tank, it comes off easily with an allen key.