PDA

View Full Version : TR4/4A How hot at radiator neck when temp gauge is reading innthe middle



tdskip
11-10-2014, 11:44 AM
Good morning guys, hope all is well. Anyone have a reading that can confirm that when your temp gauge is dead centered in the middle of the gauge (reading "n") that the temp at the top radiator neck is between 125-135, averaging around 130?

I am asking since the TR4a runs a bit hot according to the gauge but I'm not quite ready to fully trust the gauge.

I know I need to check the temps again once I get her hot but that isn't in the cards for a bit as I sort out other things.

Thanks!

dklawson
11-10-2014, 01:24 PM
I cannot address your specific question relative to a TR4 but in general, a 90 degree (angular) sweep Smiths gauge calibrated with C-N-H will indicate about 185 oF when the needle is in the middle of the "N" region. This is generally true for both their mechanical and electrical gauges.

The connection of the top radiator hose to the radiator header tank should be running very close to the rating of your car's thermostat as there will not have been enough run of hose to drop the temperature much.

tdskip
11-10-2014, 01:48 PM
I cannot address your specific question relative to a TR4 but in general, a 90 degree (angular) sweep Smiths gauge calibrated with C-N-H will indicate about 185 oF when the needle is in the middle of the "N" region. This is generally true for both their mechanical and electrical gauges.

The connection of the top radiator hose to the radiator header tank should be running very close to the rating of your car's thermostat as there will not have been enough run of hose to drop the temperature much.

Hi Doug, thanks for the response. Hope you are doing well.

OK - so check me on this, if my gauge is reading "N" which should equate to 185F but it is actually 130F based on the laser temp gun that would seem to suggest that when the gauge is reading "H" I'm probably some ways away from an actual "H" reading.

Come on guys - agree with me here since it is such a better answer than "Um, no, that is wishful thinking and you've got to pull the radiator etc...."

Thanks!

JerryVV
11-10-2014, 03:53 PM
My 2 cents worth. I'd use a thermometer and place it in the radiator with the cap off and measure the actual water temperature. On a TR4 the sending unit is very close to where the water enters the radiator. Doing this should give you the closest comparison between the temp gauge and the coolant. Start the engine from cold with the cap off and wait until the thermostat opens and you see good coolant flow. While those temp guns are good reference tools my opinion is that other things might have an affect on the readings.

Geo Hahn
11-10-2014, 07:07 PM
I use an LCD temperature strip on the thermostat housing to compare to the gauge:

https://i1214.photobucket.com/albums/cc499/Ahwahnee18/TR4/TempStrip_zps2739d287.jpg

There's also a flat black spot painted on there to provide a target for an IR gun.

For assessing what the gauge is telling me it makes sense to know the actual temp on the thermostat housing as that is also where the gauge sender is located.

Other areas are of interest of course, in particular the temperature drop from the top of the radiator to the bottom, also looking for any dead spots on an old radiator.

TR3driver
11-10-2014, 08:07 PM
I have an early TR4 gauge in my TR3, and the 185 mark seems to be very close to 185. I was planning to recalibrate it, but there was no need.

130F at the top of the radiator is way cool, which suggests to me that your thermostat is defective. If it was stuck closed, that might explain both the high temp on the gauge and the low temp at the radiator.

One important point is that those "laser" thermometers can be wildly inaccurate when shooting aluminum (like the thermostat housing). Should work OK on the radiator, though; or you can paint a black spot like Geo did. (Actually, even a paper sticker works pretty well.)

tdskip
11-11-2014, 12:30 AM
Huh, did not know that about the temperature gun. Will check again tomorrow on the radiator.

Thermostat is an easy fix if that is what is up. Thanks.