Im loosing Coolant...(a litttle lengthy)

[greek318is]

Hey guys,

I am loosing coolant on my 94 525i, and I can't figure out where it's leaking from; I have to fill the radiator reservoir up with water about every 3 days!

About a month ago, I had to replace my heater core. I don't think the problem is with the heater core though. I think it might either be a leak from the radiator itself, like a crack in the bottom of the radiator, or possibly coolant is leaking out of the engine somewhere (like there is a head gasket leak and the coolant is evaporating from this spot).

The car is a 1994 and only has 85k on it, so I don’t think it is anything serious; I’m just tired of having to refill the radiator with water.

One more thing, with the radiator reservoir bone dry, the car does not overheat... It’s a Mystery to me!

Can someone throw in their $.02?

[TouringDan]

A very common spot for leaks is the expansion tank. There is a rubber gasket at the base of the tank that goes bad and leaks under pressure. Another spot is the coolant-level sensor. Your best bet is to fill the tank, get the car warm, and drive it onto some ramps. Leave it running and get under it to see if you can find the leak.

[greek318is]

Excellent advice, and thanks for the swift response.

I will try that.


A very common spot for leaks is the expansion tank. There is a rubber gasket at the base of the tank that goes bad and leaks under pressure. Another spot is the coolant-level sensor. Your best bet is to fill the tank, get the car warm, and drive it onto some ramps. Leave it running and get under it to see if you can find the leak.

[slvr98 M]

Check you aux water pump. That can be easily overlooked.

[HausBimmer]

I put an air gun on my compressor and put a little air pressure into the system just by holding my hand over the radiator cap - a couple of little bursts - this almost always shows where the leak is. Sometimes a leak can be near the fan - so you can't locate it with the car running. Water pumps will sometimes leak slowly before they really start to pour.

[TouringDan]

I put an air gun on my compressor and put a little air pressure into the system just by holding my hand over the radiator cap - a couple of little bursts - this almost always shows where the leak is. Sometimes a leak can be near the fan - so you can't locate it with the car running. Water pumps will sometimes leak slowly before they really start to pour.


Excellent suggestion. I actually have a modified radiator cap for this very reason.

[Binjammin]

If you're going to use compressed air, make sure you dial back the line pressure or you can actually blow things apart. Line pressure is usually 90-125psi, cooling systems run at like 16psi. You're better off picking up a cap tester kit which will allow you to pump pressure in by hand up to the running pressure of the car. You can also modify a bike pump to do this job.


Remember, when you're pressurizing a cooling system like that you're severely stretching hoses, and that's damage you can't see.

[TouringDan]

Remember, when you're pressurizing a cooling system like that you're severely stretching hoses, and that's damage you can't see.

I simply installed a pressure gauge on a "T" that's threaded into the spare cap, with a standard compressor-fitting attached to the other port of the "T". Makes any fears of over pressurizing a thing of the past, and I think I've got $20 in the thing.

[AZDinanE34]

A very common spot for leaks is the expansion tank. There is a rubber gasket at the base of the tank that goes bad and leaks under pressure. Another spot is the coolant-level sensor. Your best bet is to fill the tank, get the car warm, and drive it onto some ramps. Leave it running and get under it to see if you can find the leak.

That is what I exactly have but its very light problem. How would you go about fixing this, since ive only had the new radiator for 2yrs now? Would you have to replace the whole expansion tank or are you able to get new rubber gaskets? Thanks.

[TouringDan]

You can simply replace the gasket. Part #17211712965 and it's about $3