TR4/4A Infrared Thermometer for Radiator Temp

[KVH]

I'm revising an earlier post because I didn't give enough (or correct) facts:

I'm not seeing any significant difference with my infrared thermometer, top to bottom, but that could be due to the opening temperature of the thermostat which I believe is 180--and I keep shutting down the engine once my gadget reads 192 or higher.

When I'm near the redline on the gauge, I get 162 on top and 158 to 161 on bottom. Not very helpful.

When I allow the car to idle longer, however, the upper temp goes to about 193 (before I turn off the engine fearing damage), but the bottom was in the range of 178, and I don't imagine that shows any significant cooling--or is very helpful in the analysis.

I don't imagine the radiator can cool the water at idle anywhere in the summer in Arizona, anyway.

Every time I've removed a thermostat to check it, it's been fine, so I'm reluctant to jump to conclusions here. Except for the idling test, I took the readings after a good drive where the temp gauge was at 3/4, near, but not on, the red mark.

Maybe the question I should ask is what the best test should be for my thermostat operation? What temperature disparities at idle should I see when it's near redline? I don't think what I was doing is telling me anything.

Thanks for any ideas.

 

[dklawson]

The traditional method of testing thermostats is to suspend them by a wire into a pot of water that you heat on a stove. A trusted thermometer is also placed in the pot but try not to let it touch the bottom or sides of the pot. Monitor the thermostat and note the temperature when the t-stat starts to open and when it appears to be fully open. I don't think there are any drop-dead limits on what is acceptable but I would anticipate opening within 3 or 4 degrees F of the thermostat's rating and maybe twice that range for the transition from fully closed to fully open.

What else have you done to/with the car and its cooling system? I am not familiar with TR4 cooling systems so my first question is... can the fan be put on backwards? If so, it would still move air but at reduced volume. Is the fan shrouded or open? If open, can you add a shroud to duct the flow of air through the core? Also have you back flushed the radiator and engine to leave it as clean as possible?

 

[CJD]

It sounds like insufficient air flow through the radiator. From your numbers, the most cooling you're getting from the radiator is a 15 degree drop. I don't know how much you should get, but that sounds insufficient.

Even with insufficient airflow, you should still be able to tell if the thermostat is working. When you start the engine stone cold, the engine temp should stabilize at the thermostat operating temp for a few minutes. This is while it is using the cool water in the radiator. After a few minutes, when all the cool water has circulated through the engine once, the temp will start back up. That's another sign that the thermostat is working, but the radiator is not getting sufficient air to cool.

 

[Geo Hahn]

...When I'm near the redline on the gauge, I get 162 on top and 158 to 161 on bottom...

IMO: That does not sound right for 2 reasons:

1. Your gauge shouldn't get into the red zone at those temps.

2. You should see a much greater drop in rad temp top-to-bottom.

When I am checking things with the IR I always verify the gauge by pointing the gun right at the brass base of the sender -- that gives you a pretty good idea of what the gauge should read and takes the thermostat out of the equation.

As the engine warms up from cold I feel the top radiator hose -- usually pretty easy to tell when the thermostat is opening as that hose will go from warm to hot pretty quickly.

I have a head cold & spent a frustrating half day on the garage working on my non-TR British car -- otherwise I would run the TR4 and see what number I get for radiator effectiveness.

 

[KVH]

You're right. It's more like 190 when it's near the red. My upper hose has a fashionable hose "sock" on it, so I'd better get that off to make my readings more accurate. Shouldn't the temperature difference be at least 20 degrees, even at idle? And related to all this, I need a reminder about the theory behind thermostats: Is there a reason why in a hot climate it wouldn't be OK to have no thermostat at all? Doesn't the closed position just allow the engine and block/heater water to warm up.

 

[dklawson]

The t-stat allows the engine to reach an efficient engine temperature faster and as long as the rest of the cooling system is working the way it should... the t-stat sets the operating temperature of the engine. If the engine appears to be running at a higher temperature than the t-stat and the t-stat is known to be opening at the specified temperature... removing the t-stat will make the engine take longer to warm up... but it won't fix the overheating issue.

When I use an IR thermometer I determine the points where I want to make measurements, degrease them, and apply a square of black electrical tape to those spots. You want all the surfaces you're measuring have the same emissivity so the readings will be "believable".

 

[Geo Hahn]

When you think about it... the thermostat sets the lower limit of engine temperature (once it is warmed up), it has no effect on the upper limit (that is determined by the efficiency of the cooling system, air temp, engine condition, etc).

If you have an overheating problem removing the thermostat will simply make the engine take longer to overheat but it will still get there eventually.

As yes, I think a 20° drop (top to bottom) would be about right.