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marz16 1/6/2017

1997 BMW Z3 Roadster 4 Cyl 1.90L


Why is coolant leaking from Z3 BMW?

A few months ago my dad helped me replace the radiator in my 1997 Z3 BMW because it was leaking along the junction between the plastic and metal parts. I haven't driven the car much at all since then, but today I drove about 4 miles and the engine started to overheat. I stopped to open the hood and noticed that coolant seemed to be leaking out of the closed reservoir cap. I could hear sizzling noises coming from the cap. When I got home, I noticed that almost all of the coolant was gone from the reservoir (it was filled about halfway when I first stopped). Could this be a water pump issue? Alternatively, I have the reservoir cap from the previous radiator on the new radiator because the new one did not come with one. Could this be an issue with the cap not sealing completely? Do you have advice on where else the leak could be coming from and how to solve this issue?

1 Answer


Jimm 1/6/2017

Possible leak points include; hoses, the radiator, heater core, water pump, thermostat housing, head gasket, freeze plugs, automatic transmission oil cooler, cylinder head(s) and block.

Make a careful visual inspection of the entire cooling system, and then pressure test the cooling system and radiator cap - with the engine and system cold. A pressure test will reveal the leaks. A good system should hold 12 to 15 psi for 15 minutes or more with no loss in pressure.
It is important to pressure test the radiator cap, too, because a weak cap (or one with too low a pressure rating) may be the leak source.

Note: obtain a loan free coolant pressure tester from; Advance Auto, Autozone, O'Reilly and PepBoys .


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