View Full Version : TR2/3/3A TR3 Cooling System Mystery

08-09-2009, 03:09 PM
I offer to the collective wisdom of the Board my symptoms:

(I really liked BGbassplayer's post in the 160,000 posts thread: "My Triumph blah, blah, blah. Help!")

I installed a used, but tested, sleeve-type t-stat in my car as part of the restoration. I should add, at this point, that I tested the temp gauge in the same pot of water as the t-stat: it works well. Lackluster performance eventually led to the installation of a bypass hose restrictor -- great improvement.

Here's the essential wiggliness that I can't understand: When I start from dead cold in the morning, the motor runs hot, and heats up rapidly to near the third bar on the temp gauge when allowed to idle. Sounds like a partially open t-stat, doesn't it? After I let the car sit for 10 minutes, or more, the cooling system behaves <span style="font-style: italic">perfectly</span> -- and will continue to do so as long as I don't allow it to cool all the way down.

Weirdly defective t-stat, I think. So, this morning I replaced it with a NOS Smiths un-sleeved bellows type t-stat that I picked up during the three year eBay parts binge that accompanied working on my my project. It DOES THE SAME THING! First run: HOT. (Hotter than the one that I just replaced.) Come home -- wait 15 minutes. Second run: Couldn't ask for more. The car runs at 190 on a 90-degree day; in traffic, on the freeway, sitting at red lights. If it starts to creep up at a long signal, it drops right back down as soon as I begin to move.

Any one care to posit a theory? Why does my car run hot, until I stop and let it sit -- and then it runs fine?

I should add -- Of course, when I let the car sit, the temp at the t-stat housing first becomes very hot (above the third bar on the gauge) due to the hot motor and no-longer circulating coolant. That's been my only guess so far -- that the t-stat, exposed to very high temps, finally opens fully and then continues to operate as designed. But why both of them? That's too weird.

08-09-2009, 07:04 PM
Well, my TR3A engine acted a lot like that when the head gasket was leaking. From cold, it seemed like the pump wouldn't pump at all and the temperature would just climb until it boiled inside the head; which would start the pump working and it would be fine the rest of the day.

The TR3's cooling was kind of squirrely too; which I attribute to loose crud in the top of the radiator sometimes blocking tubes. Seemed like when it boiled, it would knock the crud back away from the tubes and be OK. Backflushing the radiator with all the water pressure I could muster plus 90 psi air from the shop hose seemed to solve the problem for a time, but it ran kind of hot again after that so I may need to repeat the treatment.

08-09-2009, 08:16 PM
If you have air in the system, or the t-stat (even tested) is sticking prior to opening (and you'll never tell that in a pan of water, as no water pump is pushing against it), it will do that.

I had that happen before, got to the bottom of the hill, 2 miles away, pulled over, shut it off, t-stats opened, restarted, and it was fine.

I usually (based on lots of these issues) drill a hole in the t-stat next to the moveable part, 1/8" or so.
That keeps any combustion gasses from causing a vapour lock at the t-stat, and relieves some of the water pump pressure on the back side.

May or may not help.........but Toyotas, for one, have had one of those holes (with a little rattle valve in the hole) for decades.

08-11-2009, 04:11 PM
The head gasket theory is beginning to gain a little traction. Compression test: 1: 150 - 2: 150 - 3: 130 - 4: 130. Hmmmm.

Though I don't have the usual symptoms: No appreciable coolant loss nor sweet smelling white exhaust.

Given the lackluster compression test results, I suppose the head has to come off anyway. Maybe that will help things...

08-11-2009, 05:26 PM
There is a simple test for leaking head gasket that any radiator shop can do for you. Basically it's a sniffer that checks the air in the top of the radiator for CO2 concentration. If it's higher than normal air, you know there is a combustion leak into the water jacket.

My local shop only charged $18 for the test, but I decided to buy the tool anyway. Found a used one on eBay for $30. Like this one
https://cgi.ebay.com/ebaymotors/Engine-Bl...omotiveQ5fTools (https://cgi.ebay.com/ebaymotors/Engine-Block-Leak-tester_W0QQcmdZViewItemQQ_trksidZp3286Q2ec0Q2em14Q QhashZitem4a99dc322aQQitemZ320408924714QQptZMotors Q5fAutomotiveQ5fTools)
but without the fancy blow-molded case (and with the all-important bottle of 'test' fluid).

BTW, the head gaskets that came off the 3A didn't look "blown". Just some unexplained dark coloration in places. Basically only leaking a little bit, and only under peak pressure (engine running), so I could never tell the difference with a compression gauge.

Haven't got the Stag apart yet though, so I can't report on what it looks like.