mysterious coolant leak?

[mozirry]

I keep my 02' silverado parked ever since gas prices jacked up, and I drive a 96 saturn.

I drive the truck maybe a few times on a weekend to run errands, etc, but generally it sits there.

So before i stopped driving it I had these very slow coolant leaks, I would have to top off about every other week.

If the truck has been sitting there for 2 weeks, I can open the hood and the reservoir appears full, but once you start the engine, you can see all of it immediately get sucked into the engine and then the reservoir is empty.

It takes a minute for the air to release back into the reservoir and you can see some pump back in, but generally you gotta refill.


WTF is going on and how serious is this? I took this to a mechanic and they could not find any noticeable leaks and did a pressure test for hours and could not find anything.

 

[bruceb]

When the mechanic does a Pressure Test, his tester goes in place of the factory radiator pressure cap.
So since he finds no leaks, first thing I would try is a new Pressure Cap. You can also add Ultraviolet Dye
to the coolant, which can then be tracked with a UV Light (electric / 12V or battery type) to see where the
leak is. It is also possible the coolant is very slowly getting burned inside the motor. And don't forget to check
all the hoses for small cracks or for loose clamps. Could also be a very small leak in the heater core.

 

[mozirry]

thanks, I think those are pretty cheap, will pick one up and try it out =)

I can't imagine it evaporating that much but I suppose it's possible. You would think that any significant leak would be detected in a pressure test

 

[dug777]

Do you need to add more coolant, or does it 'come back' once the engine is cool?

 

[mozirry]

Originally posted by: dug777
Do you need to add more coolant, or does it 'come back' once the engine is cool?

Basically, when you start the engine after it has been sitting for a long time, the coolant resevoir gets sucked dry and then when you turn off the engine, some might syphon back into the reservoir but it will be darn near empy, nowhere near where it was at when engine first started

 

[chucky2]

A UOA costs like $20+...it'll tell you for absolute certain if coolant is getting in the oil.

Chuck

 

[JeffreyLebowski]

When's the last time YOU changed the oil?

I would change it and check the consistancy color of the oil and make sure you don't have a major problem if you're loosing that much colant.

Also, a culprit in the GM's is the wheep hole on the water pump.
My ta had a coolant leak and it traced it to that. I could never find a pool of colant, because it was going out the wheep hole, and dripping at highway speeds and cooking off.

 

[JulesMaximus]

Could be the water pump.

 

[mozirry]

I've pretty much changed the oil myself every time. The color is typically a dark murky black that you would expect

What is a UOA?

 

[chucky2]

Used Oil Analysis.

You basically put at least some miles on a fresh oil change (say 1500 or so), then you send a sample in (take when hot for best results) and they'll do an elemental analysis on the oil.

K and NA are in most coolants, and I think K is in almost every one. Conversely, there is no or extremely small amounts (like, low single digit ppm) of K in PCMO. So if you send in a sample, they test it and send the results back, and you've got higher than low teens double digits of K, you know you're getting coolant in the oil.

If you get your analysis back and there's no K or NA, or the ppm is mid to low single digits, your disappearing coolant isn't getting into your oil, and you've got a leak leaking externally somewhere.

Chuck