I have been having a random overheating/coolant issue since I've gotten the car out this year from sitting over the winter.
Stock bottom end HCI setup, 180 tstat, dual electric fans, sve radiator, coolant temp sensor is new, stock temp gauge
I noticed the car was overheating the first start of the year, which I attributed to a bad tstat and replaced, which seemed to work for a while.
However I had a friend following me the other day who told me my coolant overflow bottle was spilling out on to the ground, even though the car was running very cool 180 deg.
That cap will only open and allow overflow at very high pressure, and without very hot coolant there shouldnt be enough pressure in the system to open the cap.
To me, this would signal a head gasket issue, as it would be dumping combustion pressure into the cooling system, causing the rad cap to pressure release into the overflow,
However, my mechanic did a pressure test on the cooling system, and it held overnight without losing a lb of pressure, you would think a blown gasket would leak both ways?
This is an NA car so I doubt the heads are lifting or stretching the head bolts, it only makes around 300 hp.
After replacing the tstat, and pressure testing the coolant system I decided to see if I could replicate the issue so I drove the car for a week or 2 with no issues.
However last night when I pulled into my driveway, the car was badly overheating extremely quickly.
I had been monitoring the temps the whole ride home and it was running very cool on the stock gauge, but (luckily) as soon as I got to my house it was VERY hot. 250+ temp
This had happened over the course of one or two minutes at most.
I shut it down and let it cool for a bit, started again and it was still rapidly overheating, at idle the needle was climbing rapidly.
It was behaving exactly like a stuck closed tstat, however the tstat was already wide open the whole ride home and the car never went under temp to close the tstat.
I opened the radiator cap which was under high pressure but not enough to open the overflow valve, and the coolant that shot out was NOT 250+ temp as the gauge was showing.
The hoses and fan shroud were warm but not hot, it seemed as if the coolant in the engine was extremely hot, but in the radiator was not.
It was overheating so rapidly that I assumed it had to be either closed tstat, or the water pump not spinning, so I removed and inspected it, there is nothing wrong with the pump that I could tell.
I tested the tstat which was brand new anyways, and it operated correctly in the boiling water test.
I put the same water pump and thermostat back on today and test drove the car pretty hard and it did NOT overheat.
My experience with head gaskets leads me to believe that combustion is slowly leaking into the cooling system and creating an air pocket at the high point at the tstat, which would cause it to close because it is not submerged in hot fluid.
My mechanic is convinced a blown gasket would show in the the coolant pressure test, but has not offered a different idea for the symptoms.
We have not compression tested the cylinders, because previous owner seized the plugs into the heads, there has never been a misfire or spark related issue however.
Also, I used a test kit to test for exhaust gasses in the radiator, the blue fluid turned slightly blue green but did not turn yellow.
I would not prefer to not tear this engine down during driving season for obvious reasons.
I think its obvious that I should do a compression test, however these plugs are so stuck there is serious risk of damaging the threads or snapping them off in the head, as confirmed by my mechanic.
We are hesitant to do anything that could result in needing to pull the heads.
The car runs amazing, idles smooth, power throughout the rpms, driven hard often. It does not skip a beat or blow smoke out the exhaust at startup.
Help me decide what to do next to diagnose and correct this very intermittent and frustrating issue.
Stock bottom end HCI setup, 180 tstat, dual electric fans, sve radiator, coolant temp sensor is new, stock temp gauge
I noticed the car was overheating the first start of the year, which I attributed to a bad tstat and replaced, which seemed to work for a while.
However I had a friend following me the other day who told me my coolant overflow bottle was spilling out on to the ground, even though the car was running very cool 180 deg.
That cap will only open and allow overflow at very high pressure, and without very hot coolant there shouldnt be enough pressure in the system to open the cap.
To me, this would signal a head gasket issue, as it would be dumping combustion pressure into the cooling system, causing the rad cap to pressure release into the overflow,
However, my mechanic did a pressure test on the cooling system, and it held overnight without losing a lb of pressure, you would think a blown gasket would leak both ways?
This is an NA car so I doubt the heads are lifting or stretching the head bolts, it only makes around 300 hp.
After replacing the tstat, and pressure testing the coolant system I decided to see if I could replicate the issue so I drove the car for a week or 2 with no issues.
However last night when I pulled into my driveway, the car was badly overheating extremely quickly.
I had been monitoring the temps the whole ride home and it was running very cool on the stock gauge, but (luckily) as soon as I got to my house it was VERY hot. 250+ temp
This had happened over the course of one or two minutes at most.
I shut it down and let it cool for a bit, started again and it was still rapidly overheating, at idle the needle was climbing rapidly.
It was behaving exactly like a stuck closed tstat, however the tstat was already wide open the whole ride home and the car never went under temp to close the tstat.
I opened the radiator cap which was under high pressure but not enough to open the overflow valve, and the coolant that shot out was NOT 250+ temp as the gauge was showing.
The hoses and fan shroud were warm but not hot, it seemed as if the coolant in the engine was extremely hot, but in the radiator was not.
It was overheating so rapidly that I assumed it had to be either closed tstat, or the water pump not spinning, so I removed and inspected it, there is nothing wrong with the pump that I could tell.
I tested the tstat which was brand new anyways, and it operated correctly in the boiling water test.
I put the same water pump and thermostat back on today and test drove the car pretty hard and it did NOT overheat.
My experience with head gaskets leads me to believe that combustion is slowly leaking into the cooling system and creating an air pocket at the high point at the tstat, which would cause it to close because it is not submerged in hot fluid.
My mechanic is convinced a blown gasket would show in the the coolant pressure test, but has not offered a different idea for the symptoms.
We have not compression tested the cylinders, because previous owner seized the plugs into the heads, there has never been a misfire or spark related issue however.
Also, I used a test kit to test for exhaust gasses in the radiator, the blue fluid turned slightly blue green but did not turn yellow.
I would not prefer to not tear this engine down during driving season for obvious reasons.
I think its obvious that I should do a compression test, however these plugs are so stuck there is serious risk of damaging the threads or snapping them off in the head, as confirmed by my mechanic.
We are hesitant to do anything that could result in needing to pull the heads.
The car runs amazing, idles smooth, power throughout the rpms, driven hard often. It does not skip a beat or blow smoke out the exhaust at startup.
Help me decide what to do next to diagnose and correct this very intermittent and frustrating issue.