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TR6 Overheating TR6


Senior Member
My TR6 has never been known for overheating...I've had it 4 years and rebuilt the engine twice and it's never overheated on me except in sluggish, hard driving. For some reason I start the car up and it runs for a little while and the temp needle comes off cold and slowly begins to move up, like normal, and then after it's a few millimeters off cold all of a sudden it will move very quickly across the gauge. It still moves in a "dampened" sort of way...it doesn't just fly straight over to hot, but it moves very quickly. I replaced the thermostat, and it's still doing it.

Before I replaced the t'stat I had driven the car an hour and a half to Richmond, VA on the interstate and it did fine. When I started it to leave the next day by the time I got out of the neighborhood, the gauge was pegged to hot and it was boiling the antifreeze, so I don't think it's just a faulty sensor. I shut the car down immediately after seeing it, and I can't imagine that I drove for more than just a minute or two with it that hot, as I check the gauges regularly. The first time it overheated the other end of the hose that runs coolant to the intake manifold had slipped back from the tube fitting slightly (although it was not completely off) and was spraying coolant all over the side of the engine, but I do not know if this is what caused it to overheat, or if it did this because the coolant was so hot.


Great Pumpkin - R.I.P
Well, you shouldn't have hoses popping off, as the radiator cap is supposed to limit the pressure to what the rest of the system can withstand.

It does sound like something is keeping the coolant from circulating through the radiator as it should. Try shutting it down when the needle is around 1/2 on the gauge, and feel the radiator core. Then gingerly check the coolant level (don't remove the cap entirely but just crack it open, to bleed off the pressure without blowing coolant out).

I've seen symptoms similar to yours, caused by a head gasket leak. The accumulated combustion gases in the water jacket can "air lock" the pump and keep it from moving the coolant. But I'd look for the obvious things first, like a busted pump or a clogged radiator.


I had a similar experience a few years ago, my water pump was somewhat locked up, I suggest you loosen the belt and see if it spins freely.
My car had been sitting a long time waiting for me to finish my resto. work and this was one of the consequences, it's always better to start with the easy things when starting to diagnose. Good luck


Senior Member
It happened before changing the thermostat. And I don't think it had anything to do with an airlock, because it was working fine for about a year since the last rebuild and in that time I did nothing that would have let air into the system. Water pump should be OK, although I'll check it. It was spinning fine at the last rebuild. Also I believe the radiator was flushed and repaired during the FIRST rebuild, which has been about 3 years ago now, so not that long ago. Also, the block was thoroughly cleaned by a competent machine shop during the first rebuild, which I'm sure included all the coolant passageways, since it came back absolutely spotless.

If it's a head gasket leak (this car has a tendency to weep oil between the head and the block) could it be diagnosed by running a compression test? I have the compression numbers from right after the second rebuild to compare it to.


Great Pumpkin - R.I.P
Webb said:
If it's a head gasket leak (this car has a tendency to weep oil between the head and the block) could it be diagnosed by running a compression test? I have the compression numbers from right after the second rebuild to compare it to.
Unfortunately, no. A small leak won't lower the compression reading noticeably, and they vary somewhat anyway.

The definitive test is a gizmo that checks CO2 concentration in the radiator. Any radiator shop should be able to do it for you, mine charged me less than $20 to give me the bad news about the Stag. Or here's one on eBay for about twice that much :

With the Stag, I could keep it from overheating by driving very gently at low speeds. But getting on the freeway would produce instant steam, quicker even than the temperature gauge could follow.


A quick check to see if there is water flow, drain a little out of the radiator(if it isn't already a little low) just below the filler neck. Start the car and see if you see water flowing over the top of the fins on the radiator. If not, then check the pump. If you do, then check for a combustion leak.
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