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DougF

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Took a nice drive yesterday over many country roads. The car ran well.
Upon leaving my friend's house last night, the had been sitting for about 45 minutes and after idling for less than 5 minutes, the temp gauge spiked and the radiator cap literally blew off, emptying the majority of the coolant. Turns out, the electric fan is not working and the cap is bad.
After about a gallon of water refill, I drove home with no ill effects. The car ran cool with no misses.
What concerns me is the amount of pressure in the system that would cause that much coolant loss and the locking flange on the cap to give way. The cap isn't that old, maybe 2-3 years, but I don't remember where I got it, (big 3 or auto parts store. It's a 13 psi cap.
The radiator was tested several years ago and was good. It developed a very small leak that was most likely caused by the fan tie downs. Aluma Seal stopped the leak, but was blown out with this eruption.
I couldn't see any oil/transfer on the dipstick, will check the radiator today.
I had head gasket issues with this engine early on with no fluids transfer.
Any thoughts?
 
Was this a TR6 or TR3? 13# is a pretty strong pressure, the original TR3 cap would have been 4#, no idea what is correct on the 6.

Considering that boiling water can move a 400 ton locomotive & and an entire train at 70mph -- I'm not surprised that a stuck/failed cap could lead to some exciting water works. Glad all appears to have survived okay.
 
TR6. The sun had just gone down. Some laser lights and music would have been like front row seats at Pink Floyd.
It's been Christmas time for that car for the last 2 years.
 
Likely the engine is fine, as long as you shut it down and let it cool before adding cold water. I would probably just leave it alone, but you could have a radiator shop test for exhaust in the coolant if you want.

As noted, with no air flow over the radiator, the temperature and pressure is going to rise until something gives way. The cap was obviously supposed to vent the pressure when it reached 13 psi, apparently it didn't for some reason. I would inspect the radiator neck carefully to be sure it hasn't been damaged by the cap failing. If so, it's a fairly easy matter for a radiator shop to replace the neck.

The pressure on the system raises the boiling point of the coolant, so once the pressure drops (in this case by the cap failing), basically all of the coolant instantly flashes into steam. This is why boilers (and removing the cap from a hot engine) are so dangerous.

Personally, I would also want to run a pressure check with the new cap, to be sure it releases as it should. You were lucky this time, but next time you might have your head under the hood.

I don't know if there is an easy way on a TR6, but on my TR3 I have a pipe tee and nipple that I screw in in place of the heater valve. The tee has a Schrader valve (like a tire valve) on one side, and a pressure gauge on the top. This makes it easy to "inflate" the system until the cap starts venting pressure (proving that it will vent), and then watch the pressure afterwards to see that it does not drop too far below the cap rating. If it does, then either the cap is defective or there is a leak somewhere.
 
The front end of the engine has to come off to fix an oil leak, so I'll be pulling the radiator and have it tested and repaired or recore one on the shelf. The fan will get tested as I don't see anything that would cause it not to run.
I'm currently testing a prototype water pump, so I'll again make sure I have good flow at the rad. It's only a week old and I don't think it's an issue.

Thanks for your help!
 
It's a matter of preference, but I got rid of my 13 lb cap when I finished the new engine and went with a 6 or 7lb cap. I don't think that the old heater cores need that much pressure on them all of the time.
 
No he isn't.

Brosky, I plan to replace mine with a 7lb. unit. Probably stop at TRF this week.
 
Doug I bought one of the Mr. Gasket 7lb caps with a thermometer in the top of it. It looks cool and is pretty accurate.
 
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