Triumph Repair: TR6 Overheating In Summer, heater valve, highway performance

Question
QUESTION: Greetings Howard,

You gae great advice on my head rebuild so I'm hopinh you can me in the right direction on a cooling issue.

The details:  '75 Tr6, head rebuilt with new valves/guides and trued this spring. Carb rebuilt over winter.  Since putting all back together and getting tuning correct, the car has run very well. I'm now 2000 miles from the events above.  Plugs are good color and dry.  I'm running slightly rich.  New thrmostat, new water return line, new water doen tube, new hoses, new heater valve installed during head work.  Water pump is 2 years old since new.   Running 91 octane fuel.  Oil pressure is very good and predictable. I have the red 13 blade engine fan and I have a stock cardboard rad shroud installed.

However, since rebuild, vehicle warms up to normal temp (mid deflection) quickly.  Car runs very smoothly when warm.  Highway performance at 60 mph is nominal temp.  However, as ambient temps have gotten to the 25C (75-80 F) range, the vehicle is overheating in only short stop and go drives (less than 2-3 mins).  I have hit 3/4 gauge deflection a few times and have had to stop and let things cool off.

On two occasions I have blown the bottom hose of the rad.  In another case, the top rad hose (green hose with fabric weave) seems to have been stretched and is now leeching coolant through the weave.

The coolant seems rusty brown despite having changed it this spring and the engine seems very, very hot.  

Other than hose leaks and blow outs, I don't see any coolant.  My exhaust isn't white, the rad is dry, the water pump is turning.  I have noticed that when the car first starts, the exhaust will spit a little when it is humid (placing your hand on the exhaust gives you a number of damp carbony dots.  As the car warms up, this goes away.

Here's my logic:
-  can't be a cracked cylinder head or I'd see it in the exhaust in the form of coolant fog
-  could be a crack in the exhaust side of the head but you'd expect to lose fluid and this wouldn't explain the pressurization.
-  Water pump should be okay given less than 6k miles on it but symptoms seem to point to lack of sufficent flow through the system.

Any suggestion on how to troubleshoot and isolate this?  Or do you suggest this go to a coolant system specialist for a pressure test?

I do have an electric cooling fan kit sitting in my garage which would probably help but I can't help but wonder what's changed this summer compared to the past 4 to make this a problem.

Thanks in advance for the assistance.

nelson B
'75 TR6

The

ANSWER: Hi Nelson,
It sounds like you have covered most of the bases but you need to do this right away. Get the radiator dye from any auto parts store to test for CO in the coolant. If you have any combustion leaking into the cooling system it will tell you by turning the dye to a color noted in the directions. This could be a head gasket or a crack. If you do and have to remove the head carefully examine the gasket and if nothing is noted as a leak have the head tested by an auto machine shop for any unseen cracks by Magnaflux.

If the dye test shows no CO in the coolant I would remove the radiator and send it out to a radiator shop and ask to have it flow tested and cleaned if necessary. Also test your thermostat in a pan of water on the stove with a thermometer in the water to note the opening temp.

Howard

---------- FOLLOW-UP ----------

QUESTION: Thanks Howard,

I've never heard of the CO sensing dye.  I'll do that today and see what happens.

Last night I walked through the system hose by hose, refilled the rad, checked belts, plugs, timing.  Added a second clamp to the two hoses that have been a problem.  Nothing was found out of range.  My dynamic timing was backed to TDC so I pushed it back to 2 ATDC.

Went for a 40 mile drive in 70 F and humid evening temps.  Temp gauge was normal at all speeds above 20 mph.  Opening the heater core valve would cause the needle to move slightly to cooler.  Hard accel on the highway (4500 RPM) for 60 seconds would cause the needle to go up by 1/2 thickness to slightly above normal.

Then did 15 mins of stop and go in the neighbourhood and temps were back to normal.  

In short, evening seemed fine but ambient temps were not high.

Still worth a pressure check and rad servcing I believe.  

Thanks for the advice.

Nelson B
'75 TR6

Answer
That sounds normal, you might check one more item. Run the car to normal temp and stop and let it stabilize (higher then running temp) and relieve the pressure and put a meat thermometer in the radiator and read the actual temp and compare it to the gauge. To see that the gauge is correct.

The cooling systems on most of the MGs and Triumphs I found to be just on the edge of being sufficient as most of my experience was in FL. I bought a new "B" in 66 and the first thing I did was to add an electric pusher fan in front of the radiator. But I found it was only good in downtown heavy traffic as anything above 40 MPH, the fan was not useful.

Howard