Coolant level dropping but no found leak

[Snytsheuvel]

Hey guys,

My 88 325is will go through a quart of coolant roughly every 100 miles. I have put the UV dye in and it's showing up nowhere, pulled spark plugs to see if it was a head gasket, they are all as dirty as expected. Where could it be leaking?

[jeffnhiscars]

In to your exhaust

[M-technik-3]

Could be out your weep hole in the water pump when running and burns off on the hot engine when running.

[Snytsheuvel]

How could I test to see that is where it is leaking?

[Dalejandrino]

This exact same thing happened to me and then it turned into a head gasket leak.

[FLG]

Do a pressure test to determine where its coming form.

[Poorboyz]

Can you smell antifreeze when the car is at operating temperature? If its getting burned by exhaust you would be able to smell it

Sent from my Galaxy Nexus using Tapatalk 2

[jeffnhiscars]

The UV dye should leave its mark if the leak is external.

[jlevie]

That much coolant in 100 miles isn't going out the exhaust. The car would be laying a smoke screen if that was the case. UV dye should find a leak, but a pressure test is the definitive diagnostic. If the system holds pressure for 30 minutes it isn't leaking.

That leaves a loss of fluid via the overflow as the cause. Which in turn means that the head gasket has failed and air is pumped into the cooling system.

[TurboJake]

That much coolant in 100 miles isn't going out the exhaust. The car would be laying a smoke screen if that was the case. UV dye should find a leak, but a pressure test is the definitive diagnostic. If the system holds pressure for 30 minutes it isn't leaking.

That leaves a loss of fluid via the overflow as the cause. Which in turn means that the head gasket has failed and air is pumped into the cooling system.

Truth,

But, it could also be a bad reservoir cap that isn't properly sealing and pressurizing the system, just causing the coolant to flow out when the engine is up to temp.

OP, Does the system pressurize?

[Snytsheuvel]

I got a new expansion tank cap, made no difference

[jlevie]

It is easy enough to find out if you are loosing coolant via the overflow. Point the hose into a catch container. With a new cap in place if coolant winds up there, the head gasket has failed.

[bmwman91]

Does the engine bay reek of coolant? If it was spraying out somewhere in there you would smell it.

[Snytsheuvel]

Long story of what I learned today.

Short version:coolant may have been found in the oil

Long version: I built a pressure tester using the old cap, inner tube valve and a bike pump with a pressure gauge. I pumped pressure into the expansion tank but the gauge had no reading. Air was leaking out from the bottom of the cap only when I was pumping air. When I released the cap I found the expansion tank did indeed hold a bit of pressure. I checked the oil cap and under a UV light it was a hazy green (oil) with spots of bright green (coolant with dye color). Not finding the coolant leak anywhere externally but I didn't pressurize it very high or very long because the gauge wasn't reading.

I'm thinking head gasket. If I want to replace those myself, how much am I looking at spending?

Thanks for the help guys