Jon Schepps

I'm loosing coolant when the engine is running and the turbo is working hard. Cold coolant level is just above the minimum mark.

Seems that if the coolant can boil if it doesn't circulate AFTER the car is shut off, then certainly it can boil if it can't circulate while the engine is running.

Thanks,
Jon.

Jason_86_951

OK a few more questions:
When the car is off and the turbo water pump is running;
Can you see the coolant being pumped out of the turbo??
Does the boiling over happen during or after the water pump is running?
Does it boil over after a normal drive (20 minutes no boost)?

Jon Schepps

Jason,
Good questions.

1- Yes, the coolant is pumped properly after the engine is shut off. It'll pump for 20+ seconds or until the thermoswitch opens, whichever is longer.

2- I think I've seen it boil with the pump running. It won't boil after the pump stops (because the thermoswitch won't stop the pump if its that hot).

3- No. But this is primarily a track car and doesn't get much street use. I'd have to explicity try that to be sure, but I doubt it would.


The issue is, the head is off now, and I see no obvious gasket breach. But I discovered that the turbo output snout on the water pump is clogged with who-knows-what. Which is what led to this discussion.

I think my only choice now is to put everything back together and see if the problem goes away now that the coolant line is unobstructed. If it does, its an interesting lesson-learned. If it doesn't, then its back to the HG. But this time I'll do a hydrocarbon-in-the-coolant test before pulling the head.

Jon.

cpt_koolbeenz

Check this out. Not sure if it would cause the water not to circulate through the turbo at ALL, but it is a start.

roadrunner

I'm not sure that the amount of coolant being vaporized in the turbo cooling circuit will be enough to blow the coolant out of the expansion tank. As soon as the small amount of vaporized coolant contacts the much larger amount of coolant in the rest of the system, it will condense back into liquid. It sounds more like a head gasket leak or the block/head are compromised, or a loss of pressurization due to a bad cap or a leak.

Waterguy

I had the same thought as Chris. Can you see/hear the coolant circulate back to the reservoir when the turbo water pump runs, or can you just hear the pump run?

MachSchnell

I see a lot of things replaced, but no mention of the actual expansion tank...any chance you have a mild crack in the lower seal fitting for the cap in the expansion tank? I've been thinking this might be my problem, as I seem to encounter the same problem at random times after the car is shut off...it might go 3 weeks and never leak a drop, then one day after mellow driving I'll find a coolant puddle under the car...I'll refill it, and go another week, 2, 3, who knows before it happens again. Your turbo water pump theory is intriguing, my pump is new but the temp sensor is not, so perhaps that is a culprit, but I have a new expansion tank waiting to go in and am hoping this fixes the problem.

cpt_koolbeenz

Very good point Jason... I know he is not looking for troubleshooting, but he is getting some good points anyway.

Brian S.

I know you are not looking for a diagnosis, but thought I'd chime in.......I had the same problem and assumed it was the head gasket, but my mechanic found that there was a blockage within the actual radiator. It was in rough shape, so I replaced it........haven't had a problem since.

Peckster

Have you done a leak down test? There can be a slight leak between the cylinder and a water passage that won't be readily apparent when you remove the head.

I won't say hah again.

Jon Schepps

Let me catch up on some answers:

cpt_: That's an appropriate link because that's where my constriction is. That poster apparently didn't know that the plastic snout serves as a blockoff plate for the NA cars, and must be drilled out for the turbo cars. In my case, there was either some residual gunk in the new waterpump I installed, or some gunk in the hose that I didn't notice.

roadrunner: Yes, and no. Yes, in that the relatively small amount of coolant that gets boiled at the turbo will not raise the temperature of the entire cooling system. But no, I'm convinced it will definately raise the pressure in the expansion tank. When that water boils, and the feed hose is constricted, the gasses have no place to go but into the exp. tank that is only a few inches of hose away. Others here have witnessed this when their t-pump or thermoswitch failed.

Waterguy: Yes, the pump runs normally, and water circulates between it and the exp. tank just fine.

MachSchnell: That was part of the etc.'s. New exp. tank. Not that the old one was leaking, just so yellowed from age/heat that I could hardly see through it. There are no coolant leaks, other than what pees out the overflow tube.

cpt_: Yes, didn't want this to turn into a troubleshooting exercise, because this has been a long-standing issue and I've done ALL the usual stuff. And yes, lot's of good insights and discussion in these forums. Very appreciated.

Brian S.: Yup... so here's another case where conventional wisdom may have replaced a perfectly good HG (don't know the particulars though), to no avail.

Peckster: Yes, leakdown <2% in all cylinders (head had recently been re-worked).

Today's mission is to put it all back together and see what happens. I'll report back.

Thanks everyone for your suggestions!

Jon.

Songzzz

Jon, same problem last year with my 2.5 motor with an oilcooled only turbo. See my earlier post to this thread.

Jon Schepps

Here's an update.

Everything's all back together, sans blockage in coolant line. I only had about 10 minutes of daylight left and I didn't want to be driving around a just-back-together motor in the dark . I did lots of repeated full boost sprints. No fluid out the overflow. Yet.

I'm not declaring victory until I can stress the system a lot more, but so far so good.

Jon.

cpt_koolbeenz

<<<sans blockage in coolant line>>>

What does that mean?

Jon Schepps

sans = without (latin?)... sorry for the obscure language.

Wherever this goop came from, it was sitting in the output tube of the plastic snout on the engine water pump (that houses the small turbo thermostat), and the first inch or so of the rubber hose that connects to it.

So the only significant difference between the car now and how it was a week ago is that this coolant path to the turbo is now unrestricted.

Jon.