View Full Version : TR2/3/3A TR 3A running hot at high rpm

06-20-2018, 11:42 AM

My TR 3A engine is running hot at highway speeds. Generally, below 70 mph (3000 rpm) the engine runs around 190 to 195 degrees. Over 70 mph, the engine temperature goes up to between 205 and 215 degrees.

The engine was rebuilt about 1000 miles ago, the radiator has been rodded out, and the engine is using a sleeved thermostat. Timing and air/fuel mixture are fine. Air deflectors to the radiator are installed correctly.

A friend is have similar issues with his TR 3A even with a new radiator (with crank hole). He also has installed the Macy’s Garage cooling fan, not that it would have any bearing at highway speeds.

It has been suggested that perhaps the water pump is moving the coolant too fast at higher rpms, thus not allowing the coolant to hang out in the radiator long enough to bet cooled off.

Any suggestions other than drive slower?

06-20-2018, 12:16 PM
First question, does your grille have the larger openings? https://www.tr3a.info/FAQ_grill.html

How do you know the mixture is "fine" ? Have you checked it under the conditions where the problem shows up? Were the carb needles and jets replaced? Wear in them can be very hard to detect, but can make the mixture go lean under cruise conditions.

How do you know the temp gauge is accurate? They often read high.

Have you checked that the timing is advancing as it should?

Original style radiator core?

Coolant moving "too fast" is a myth, IMO. Violates laws of thermodynamics. You can get situations where trying to move it too fast can cause problems, like the radiator hose on the suction side collapsing; or the dynamic head at the top of the radiator going high enough to force water out past the pressure cap. Cavitation in the water pump is another possibility.

Yet another possibility, with the stock aneroid type thermostat, is excess pressure blowing the thermostat closed. They aren't very good thermostats anyway, according to the book they start to open at 158F but don't get fully open until 197F

I would probably start by trying to verify the temp gauge. Get a cheap infrared thermometer and check the temperature of the cylinder head and upper radiator tank with the engine hot. Aluminum will fool them, so you can't shoot the thermostat housing directly, but a piece of masking tape will give you a good target.

06-20-2018, 02:52 PM
Hi Randall.
The grill is the original to the car, or at least the same grill as before the engine overhaul.
Temp gauge was recently rebuilt after I broke the capillary tube at the sensor. Car overheated prior to me breaking the capillary tube.
Carbs were set using a chassis dyno, including both low and high rpm.
Timing set using dial-back timing light; checked at low and high rpm.

My car has the original style radiator, as does my friend’s car with a new, original style, radiator.

After an hour driving at between 65 and 75 mph, the radiator gurgles when I shut the car off, and coolant runs out the overflow drain tube.

06-20-2018, 03:12 PM
Sounds like you've covered most of the bases pretty well. Only thing I see left is that original radiator. They didn't solder the tubes to the fins, instead the tubes are just pushed into holes through the fins. On my 3A, that joint was apparently no longer making good thermal contact. I couldn't make it anywhere near an hour at 75, more like 15 minutes max on a cool day. Having the radiator recored with a modern style core made all my cooling problems vanish like magic. Along with the other upgrades I installed along the way, it would stay under 195 no matter what the conditions (even running 100+ mph in 100+ heat through the desert).

The other thing I might question is whether the radiator shop did actually rod it out. When I moved that same recored radiator from the wrecked 3A to my current TR3, I first took it to the radiator shop and told them to service it "Do what it needs". When I asked about what they had done, the tech said that it "flowed fine", so they hadn't bothered to actually rod it out. Well, it didn't cool so good any more! After fighting with it for a long time (including taking it back to the shop twice), I finally insisted that they rod it. "Ok, but it won't help". Kurt called me to apologize in person, turned out they couldn't even get the rods through the tubes! On his advice, I had it recored again and once again all my cooling problems disappeared like magic. They said the tubes were coated inside (but not blocked) with "mud"; which I am guessing was partly stop leak mixed with rust particles and crud.

Sure surprised me, as I hadn't noticed any trouble at all with it before the accident. Evidently, the "mud" formed during the years it sat in my driveway (under a cover) waiting to be parted out.

06-20-2018, 04:49 PM
I once had a Nissan radiator rodded out that was 4 years old. I lasted one year before it started overheating again I took it a different shop and they called to say they could not get the rods through the tubes. So I guess the first guy didn't give a sh**. A new Auto Zone radiator cured the problem and lasted for many may years.

06-20-2018, 04:53 PM
Coolant moving "too fast" is a myth, IMO. Violates laws of thermodynamics. You can get situations where trying to move it too fast can cause problems, like the radiator hose on the suction side collapsing; or the dynamic head at the top of the radiator going high enough to force water out past the pressure cap. Cavitation in the water pump is another possibility.

Except....part of the laws is the heat has to transfer. Which means contact.
Example...run your finger rapidly through a flame. No burn because no heat transfer.
While in a little British four cylinder built for roads with slow speeds and cooler weather heat transfer might never be a concern....in some cars it is.

I do Flathead Fords.
Four radiator hoses. Two water pumps.
Two thermostats.

Remove the restriction of the stats by removing the stats, flow too high.
It will overheat.

Rebuilding water pumps and grinding off every other impeller blade usually fixes it, but in racing they also drill a whole lot of holes on the impeller in addition to grinding off blades.

Been fighting those gremlins for over 50 years.

06-20-2018, 05:09 PM
Yes, it's true, each finger-width of water picks up less heat as it flows through the engine. It also gives off less heat as it flows through the radiator.

But, there are also more finger-widths of water making the trip every minute. A lot of little pieces (of heat transfer) adds up to the same as a few big pieces.

I don't know what the problem is with your flathead Ford motors. But the folks at FlowKooler seem to think it was lack of dynamic pressure in the cylinder block.

06-20-2018, 05:13 PM
While it sounds like your radiator is flow restricted, try removing the thermostat. I have run a number of cars (including both my TR3s and a bunch of MGBs during a BMC overheating recall in the 70s) and it always helped the cooling. As for the finger-in-a-flame analogy, it is more apt if you consider it with a heat absorbing material in the flame. Put a piece of iron in the flame for a short time and it takes a short time to cool in air; put it in the flame for a longer time and it will take longer to cool. Bob

06-20-2018, 05:17 PM
If the gauges are calibrated correct, my guess would be the thermostat because none of that makes sense. 70, is not that fast and the air at 70 should do something to cool it. Just try a cheapie thermostat with a hole drilled in it for flow to see if there is an effect.

06-20-2018, 05:48 PM
I understand your thinking the timing is correctly set, but only a little to far advanced can cause the the engine to retain the combustion just long to raise the coolant temp. You might retard the setting slightly.

06-20-2018, 06:53 PM
How old is your radiator................A NEW radiator core is a worthwhile $ investment even if it does not cure the problem.

06-20-2018, 08:36 PM
one more thought. Fan belt.
Higher speeds, more drag on water pump.
Checked belt and tension, just to eliminate?

06-20-2018, 08:55 PM
And wear on the side flanges of the water pump pulley. Is the belt riding on the flanges or on the root of the pulley.