Stumped on cooling system problem

[2 8]

96 MK3 Cabrio 2.0 ABA

Started out with a pin hole leak in a coolant line. Ended up losing a lot of coolant.

refilled, but car kept overheating. Thought it might be an air bubble and bled system several times. squeezing hoses, filling upper rad hose etc.

Replaced thermostat and checked water pump. Both good.

Thought maybe it was a bad head gasket. Did a compression test and it was 180-190 across the board.


Right now if I let it idle with the reservoir cap off it bubbles out and seems like it is boiling almost. The car sits at operating temp with cap off If I put the cap on the car will overheat.

lower rad hose is cool, upper rad hose is hot.

heater is blowing COLD. Drivers side heatercore hose is hot. Passenger side heatercore hose is cold.

Temp sensor on radiator appears to stay cool. Fans only kick on if AC is turned on.

All help appreciated

[iadubber]

sounds like a blockage in the core somewhere, which seems very unlikely. Was this a rebuilder at one time?

[2 8]

it was in an accident like 20k miles ago.. very minor. Hood, headlights, grill replaced. Wouldn't have anything to do with this problem.

I guess if the core is clogged I could bypass it and connect the two hoses for a test

[OrangeDUB]

Could be a clogged radiator

[kleinergti1]

could still be a head gasket even with good compession.

[2 8]

i know it could still be a HG with the good compression, but that was the quickest test I could do. Bad HG wouldn't explain no heat though... I am pretty certain it is a circulation issue

[GetAwayFromMe]

If the lower rad hose is cool than the coolant isnt flowing through. Like Kleinergti1 said even with good compression test there is still a chance of a blown headgasket. I would fix the radiator problem and go from there. I would also flush the heathercore looks like you have a problem there which could also cause it to overheat.

Good luck

[GetAwayFromMe]

I don't think i ever had the car overheat because the heathercore was pluged but it's possible.

[Black86gti]

air bubble stuck in the water pump not allowing any flow. but its probably a clogged core. bypass the core and check and if looks good you can try to back flush the core and see if you can get rid of the blockage shaving you th etime to pull the core out to replace

[vwmeister]

i know it could still be a HG with the good compression, but that was the quickest test I could do. Bad HG wouldn't explain no heat though... I am pretty certain it is a circulation issue


Just wondering how you ''checked'' your water pump?

[2 8]

Just wondering how you ''checked'' your water pump?

I was able to see the water pump fins through the hole where the thermostat sits. I'm not a mechanic, but it appeared to be in good condition and was spinning as should with the pulley.

[iadubber]

I was able to see the water pump fins through the hole where the thermostat sits. I'm not a mechanic, but it appeared to be in good condition and was spinning as should with the pulley.

I wouldn't say that's a good test of a water pump. Is there any play in the shaft? Does it spin freely? Was there coolant in the system when you did this test?

[2 8]

I wouldn't say that's a good test of a water pump. Is there any play in the shaft? Does it spin freely? Was there coolant in the system when you did this test? Yes I spun it and it was solid, no shaft play. The pump looked and felt good and solid.

May have figured it out. I blew some more compressed air through the system and I think I may have unclogged whatever debris or air bubble was in there. Took it for a long drive and no overheating as of yet.

[Fick]

I had this same problem, when my car was idle for a long time the temp would go up and it would get really hot. So I replaced the water pump at home and it seemed to fix it and I found a leak in a hose and I have since then not had it overheat once.