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boeingpilot

boeingpilot

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I went out for a drive in my '67 TR4A last week and after about 30 minutes noticed the temp climbing rapidly. Got home to discover the top radiator hose had split. Hmmm. Ordered a new one from Moss and installed it today. Flushed and filled the cooling system and went for a test drive. After about a mile and a half the temp started climbing again. I stopped and open the bonnet to find coolant boiling up through the head bolts!

What the deuce!?!

My first guess was that the 13 PSI radiator cap did not open causing the pressure to build in the system and ultimately pushing it out through the head bolt holes. The overflow bottle was about 3/4 full and there was noting coming out of the radiator cap.

Before I start disassembling things I thought I would solicit advice from those more knowledgeable than myself (which means everyone)....
 
More likely, IMO, the first overheating episode damaged the head gasket or cracked the head. It's unlikely that a cap would fail to open (generally they fail by not holding pressure at all), and even more unlikely that your hoses and radiator would hold anywhere close to the pressure that the head gasket sees on a regular basis.

At any rate, the head is going to have to come off, IMO.
 
Sounds like the thermostat has failed, backing up coolant in the engine.

Soon the engine becomes stinking hot and coolant can sometimes be seen bubbling out through the exposed head studs on the manifold side.

It's worth considering returning to a standard 7 PSI TR4A radiator cap, as a 13 PSI cap nearly doubles the factory set coolant pressure.

Viv.
 
Viv -

That's exactly where the coolant was bubbling, on the manifold side of the head. I didn't know the standard TR4A cap was rated for 7PSI. This is the cap that came with the car so I just assumed it was correct. Thanx for the info.
 
I would be worried about damage to the cylinder head gasket. I think the head is solid enough not to warp. Could you run the car without the radiator cap for a while to see if that helps?
 
Maybe it's hopeful thinking on my part, but I don't think the head is warped as it never completely overheated. I shut it off before the needle got into the red, but who knows. I did run the engine with radiator cap off and it tried to overheat again. My plan is to pull the head off and make sure it's not cracked or warped and see where things go from there.
 
Possibly air in the system now.
Before the engine heats up try pulling the return heater hose off while the engine is running (open the heater valve first)
Then try pulling the top hose off and see if the coolant starts flowing as the t'stat opens as the engine warms up; no flow means a dud t'stat.
 
Off with her head!

If you want confirmation there is a tool for checking combustion gases in the coolant available from NAPA, etc. Simple kit, uses a reactant to turn color if combustion gases are intruding into the coolant.

But if coolant is intruding into head bolt holes that's pretty conclusive the head gasket integrity is compromised.
 
DrEntropy said:
If you want confirmation there is a tool for checking combustion gases in the coolant available from NAPA, etc.
Click to expand...
FWIW, my local radiator shop only charged me $18 to do the test, while FLAPS wanted some $80 for the tool & a bottle of test fluid. I bought a used one on eBay instead.

If you do buy one, check that it comes with fresh test fluid and instructions.
https://www.amazon.com/UVIEW-560000-Combustion-Leak-Tester/dp/B000NPDL76
 
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