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Discussion summary
YOUR RESEARCHCoolant expansion broken? How to diagnose?
Leading reported evidence
Replace waterpump i noticed this during the bleed routine
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Performed · outcome unconfirmed · Original poster
I have never had any obvious coolant leaks but when I replaced the waterpump I noticed this during the bleed routine.
Leading evidence: 'Replace waterpump i noticed this during the bleed routine' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'coolant expansion tank is broken' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Replace waterpump i noticed this during the bleed routine' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suspected cause · Original poster
What I suspect happens is that once the pressure is removed the volume increases (PV=nRT), and this causes coolant to flush out of some leak.
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Suggestion
My advice is pressure test the system, the leak should show it's butt after pressure is applied.
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Hi,
I suspect my coolant expansion tank is broken.
If I slightly remove the cap once the engine is warm (91 degrees) there is coolant spitting out over the headers on the left side. I can't see the leak from the tank or from any hoses, it's really cramped in there.
But it drips out of behind the plate that covers the coils, not sure how it ends up there.
What I suspect happens is that once the pressure is removed the volume increases (PV=nRT), and this causes coolant to flush out of some leak.
I have never had any obvious coolant leaks but when I replaced the waterpump I noticed this during the bleed routine. I haven't experienced any leaks, so maybe it's when coolant reaches a certain level.
Is there any clever way of diagnosing?
I've experience a cracked expansion tank. Not something you want to ignore. I'm not sure it's smart to unloosen the cap while it warm. I seen a guy do that once.... ONCE!
My advice is pressure test the system, the leak should show it's butt after pressure is applied. But if you haven't replaced the tank in a long time, then I'd plan on replacing it now. Also, purchase a new coolant level sensor and updated cap.
Cheers!
It's part of the bleed procedure to slightly open the cap when it's warm. There is no harm in doing it if you do it slowly and carefully, only loosen it slightly to let some air in. But thank you for the warning, I can see how it's a disaster if not done right.
Maybe I should just replace it as a maintenance item and hope for the best. One simple think I will try is to overfill it and see what happens.
But there is no other obvious place in the engine on that side that can spit coolant when engine is off?
There's an overflow drain hose from the coolant tank dangling all the way to the coils heat shield. If the coolant is coming out from that hose, it could be normal. The coolant cap should open when the pressure inside the tank is around 20PSIG or so. There is really no need to open the CAP for bleeding. Just pop up the bleeder valve and keep it there and drive for a few days. Note that bleeder valve does not vent but the coolant cap is designed to.
Bleeder valve burps the air out of the system. Open manually by propping up wire bale on the top and leave it open for several heat/cool cycles. Do you have the latest cap, blue and ending in 04?
No, the bleeder valve does NOT vent to the atmosphere (the cap does when pressure exceeds ~20PSIG). The bleeder (while open) connects the air vent (from engine, radiator, oil bleeder, etc.) to the tank so any air trapped in those places will be vented into the tank.
Under normal operation, that vent valve will open whenever the internal pressure is around 6~10PSI so even if you don't prop it up, it will open on its own. The reason to manually prop it up is so that even before the coolant gets hot, any air trapped can escape into the tank.
100% having cap loose is NOT part of the bleed procedure in anyway. In fact you could be causing remote boiling.
Bleeder valve does exactly what it sounds like, that is its purpose...leave the fill cap tight always
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