TR4/4A Water temperature and electric fan in a TR4

[jimstr4]

Hello All, It's been a while since I contributed in any way on this site so here goes.
Many years ago I decided to upgrade my cooling system since it overheated quite nicely in stop start traffic.
So I added an electric thermally controlled fan and removed the plastic TR6 fan.
That was a waste of time as the generator was useless at supplying current at low revs, with the ammeter always in the negative at low revs if the fan was on.
So I used to turn the engine off and wait for the traffic ahead to move, then start again and move the TR.
I decided to restore the car so I had the engine reconditioned and the radiator recored.
Alas I made the mistake of leaving the crank handle hole in.
Next step was an alternator, I added a Lucas 17AR (I think it was a 17AR) with a belt adjustment thingy from Rimmers.
Kept my wide belt and decided not to go for a Dynamator after I heard that they aren't reliable.
Started the car and set the fan to come on at 190F. I then decided to test the accuracy of the water temp gauge and sender by immersing a meat thermometer in the neck of of my long neck radiator.
Yes I know it's not an accurate method or thermometer and got a gauge reading of about 190F and a meat thermometer reading of about 160F.
I understand that a TR4 engine operating temp should be about 190F.
So can I be bothered getting a more accurate thermometer to test again.
Is the mark on the temp gauge between 185 and 250F about 210F?
I suppose I should set the fan control to come on at about 210 instead of 190F if the temp on the gauge is that far out.

Jim and the still off the road 1962 TR4

 

[TR3driver]

I think you are over-thinking this, Jim. Most of the time, the coolant temperature will be controlled by the coolant thermostat, not the fan thermostat.

I use a TR4 temp gauge in my TR3, and a modern 185F thermostat. Under normal driving conditions (sustained speeds over 25 mph or so), the gauge rises only until the thermostat opens, which is at the 185 mark on the gauge. I then set the fan thermostat to come on slightly above that, at about the '5' in "185" (roughly 190F). Result works quite well, for me. The fan only runs in stop and go traffic, or when I'm sitting at a stop light for more than a minute or two.

185 is warm enough, there is no useful difference between 185 and 190 as far as engine operation goes.

 

[jimstr4]

I replied to Randall's comments but I'm not sure where it went so at the risk of repeating myself, Thankyou for the reply.
I suppose my question was more about the accuracy of the temp gauge and sender, if the gauge/sender are reading 20 - 30F too high then I have a bigger safety margin than I anticipated re cooking the engine.
Alot of car temp gauges don't state the actual temp but simply have something like C and H on the gauge dial, no numbers.

 

[TR3driver]

One way to check that accuracy (even with no numbers on the gauge, you can remember roughly the needle position or even make a mark on the glass) is to watch where the thermostat opens. Modern thermostats are usually pretty good about opening close to their rated temperature, and it's not hard to see how the gauge climbs steadily when you start driving from cold; then slows and stops as the thermostat opens.

Non-contact (infrared or 'laser') thermometers are relatively cheap these days, but they have their own problems with accuracy. Old aluminum in particular confuses them, so you won't get an accurate reading from the thermostat housing (for example). But they work much better on other surfaces, like cast iron or rubber (hoses).

I have been known to test thermostats, gauges and sensors by boiling in a pot of water; but that is kind of tricky too. You can't take a reliable reading while the water is being heated, because the temperature is not even. Better to heat it past the temperature you are interested in, then take your reading as it slowly cools.

All 3 of those methods say the early TR4 temp gauge that I have is pretty close to right on. Doesn't necessarily mean yours is too, of course, but it might be.

If not, it's actually possible to recalibrate the gauge. You can read more about that process here
https://www.triumphexp.com/phorum/read.php?9,1405143

 

[TexasKnucklehead]

Jim, I think both you and Randall are over thinking this a bit.

You are correct that sticking a thermometer into the neck of the radiator is not the best approach to test the accuracy of the dash mounted gauge. Mostly because you are measuring something different than what the gauge is measuring. The gauge is measuring the temperature of the coolant inside the engine, specifically as it passes the sender unit near the exhaust of the internal thermostat. Measuring the temperature of the coolant at the neck of the radiator has little to do with the temperature of the engine. The coolant temperature should be much lower than the engine temperature if it's expected to help keep the engine from overheating.

I too have tested the accuracy of both the thermostat and sending unit/gauge with boiling water as well as another measuring device. -And the gauge was fairly close. It's also possible to use a thermal IR gun pointed at a clean engine block to get a reasonable reading. You can also use a hand held meter with a thermal probe to get a fairly accurate reading. But, in every case, you should find the temperature of the coolant in the radiator to be much cooler than the temperature of the engine.

Remember, the engine temperature is set by the thermostat, and that is what the temperature gauge should be showing -not the temperature of the coolant in the radiator.

 

[jimstr4]

Thankyou for the replies, sounds like I should leave well enough alone.
If the normal operating temperature is 185F ish then I'll set the fan to come on at about 195 - 200F.
By the way I'm glad I changed to an alternator, when the fan comes on the alternator kicks in and pumps in the current even at low revs.