TR6 Overheating TR6

[Webb]

I posted about this over the summer and still have not had it fixed. Long and short of it is that the car runs fine, but when started from cold, the temp needle begins to move up normally, the after about 5 or 6 minutes of running it just rockets to red. It's not the gauge or sending unit. It really is overheating. I've replaced the thermostat already to no avail. Obviously the sending unit and gauge are ruled out since it really is overheating. Engine was recently rebuilt and all passages in the engine are clear. Engine compression is fine and it's not blowing any color smoke whatsoever. I took the fan belt off and turned the water pump by hand, and it turned easily, without hanging up. No lateral movement at all, very solid. I could feel a tiny bit of resistance in a certain area, but nothing significant.

I'm beginning to think it HAS to be within the radiator somewhere. Any other guesses?

 

[tdskip]

Well with everything else you have done the radiator stands out. Have you flushed / back flushed it?

Is it original?

 

[Mickey Richaud]

Air pocket in the system?

 

[Mickey Richaud]

Another thought that occurred to me is you may have a hose that's collapsing.

 

[Andrew Mace]

Well with everything else you have done the radiator stands out. Have you flushed / back flushed it?

It would be worth flushing, not only to see what might come out of the radiator but also what might come out of the block, despite the recent rebuild. If that doesn't help, my next step would be to have the radiator boiled out, rodded out, or even recored.

And forgive me, but I'm assuming that when you say it really "is overheating," you're confirming that either by watching the coolant boil out or checking the temperature of said coolant?

 

[TexasKnucklehead]

the temp needle begins to move up normally, the after about 5 or 6 minutes of running it just rockets to red.

Rockets to red?

Why would the temperature change suddenly increase? My guess is you've got an air pocket in the line. As soon as the thermostat opens, hot air enters, instead of coolant. I used to pull the tr6 onto a set of car ramps when filling the system with coolant. It's hard to get the cap higher than the thermostat. -Either that or find a way to burb it.

 

[DougF]

If you have access to an infrared thermometer, take temperature readings at all corners and several places in between on the radiator. You will be able to tell if there are any blockages.

 

[DNK]

Take the thermostat out and insert an aspirin in in it to keep it open and reinstal. Turn on the car and fill the rad. until full let it run and top off as needed. The aspirin will dissolve and your good to go.

 

[Tinster]

This non-mechanic guy would remove the radiator cap,
crank the engine up and then peer into the radiator fill
hole and watch to see if water is really circulating.

The same "know not-alot" guy would also probably
have my infrared pistol in hand and shoot all over
the place looking for hot ot cold spots.

I would do this test with and without a thermostat
in the coolant system.

<span style="color: #000099">Then I'd replace the radiator, replace the
temp sending unit, replace the temp gauge, replace all
hoses, replace the thermostat, replace the water pump,
refurbish the water pump housing, replace the radiator cap
and finally--- install a new fanbelt and rebuild the
front suspension.

My car never overheats anymore.</span>

dale :thumbsup:

 

[TR3driver]

FWIW, My Stag has rather similar symptoms; which I've traced to a leaking headgasket (and/or warped head). Doesn't leak enough to affect power or compression readings, but lets combustion gases into the coolant when under power. Under some circumstances, enough gets into the coolant to air lock the water pump, resulting in instant boilover (sometimes I can even see the steam before the gauge hits the red).

I wouldn't think a TR6 would act that way, since the pump is mounted lower; but if all else fails, it might be worth having the radiator tested for combustion gases. Any radiator shop should be able to do the test in just a few minutes, mine charged me $15. Later I bought the tool on ebay, for about twice that.

Also FWIW, an alternative to the aspirin trick is to drill a small hole in the thermostat backing plate, then install the thermostat with the hole at the top. Some thermostats already have the hole, but most do not. It does slow engine warm up slightly, but makes filling the cooling system much easier.

 

[aeronca65t]

Make sure your lower rad hose isn't sucking closed when the thermostat opens.

Watch it as the car warms up.

The lower hose should have a spring inside it to prevent collapsing, but some aftermarket units do not (or on old hoses, the spring tears the inner rubber causing a restriction).

 

[2wrench]

Take the thermostat out and insert an aspirin in in it to keep it open and reinstal. Turn on the car and fill the rad. until full let it run and top off as needed. The aspirin will dissolve and your good to go.

Give it one aspirin and call Don in the morning.

Seriously, just another thought would be to open your heater control valve to circulate
water/coolant through the heater core to further dispell any ideas of air pockets.

 

[dklawson]

Take the thermostat out and insert an aspirin in in it to keep it open and reinstal. Turn on the car and fill the rad. until full let it run and top off as needed. The aspirin will dissolve and your good to go.

I remember that from "The Puzzler" on Car Talk many years ago. At the time I had a Honda with a cooling system bleed nipple. I thought the aspirin trick sounded like an excellent fix for cars w/o the bleed nipple.

 

[Mickey Richaud]

Awright, Webb - SHEESH! It's been almost 18 hours! You're running up quite a tab here, with all this expensive consulting work! So, what's the story?