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TR4/4A TR4a cooling questions

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tdskip

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Hi guys - the gauge on the '67 TR4a shows I am running hot. New engine, new water pump, re-cored radiator and all that good stuff for background.

Here is what the gauge shows (car is not running - no need to freak out over the oil pressure - grin)



But here is the reading at the radiator reading +/- 150 degrees.



Now I know that the temp pick-up is on the radiator housing which will be hotter than where the thermometer is located in this picture, but that seems like a big difference between the gauge and the radiator. Any thoughts or coaching to pass along?

Thanks!
 
It's been a very long time, but my 67 overheated or rather ran on the hot side and 2 things cooled it down...a new radiator shroud and a timing adjustment. I just bought another 67 and I'm sure I'll probably experience the same thing once I get it running.
Rut
 
Any ideas to the sendering unit? I have had some that did not match the guage and made the temp read high. I recomend changing sending unit out before doing anything else.

marv
 
Hi Marv - any easy way to check and see which one I have on there right now? Can they be visually identified?
 
I agree with Marv, first thing is to verify the accuracy of the gauge. Those hot wire gauges are notoriously inaccurate, in addition to the sender problem he mentioned. Last time I looked into it, there were something like 6 different senders originally, all of which are now cross-referenced to the same replacement.

Have you verified that the so-called voltage stabilizer is working? They usually fail closed (when they fail), which makes both temp and fuel read about 1/4 scale too high. A bad ground (to the VS) can do the same thing.

A somewhat crude test for the overall gauge system is to start the engine from cold and monitor the radiator core. The core should stay cold as the engine starts to warm up, because the thermostat is closed and blocking water flow through the radiator. Then at some point the radiator should suddenly get quite warm as the thermostat cracks open. When that happens, immediately check the gauge reading. It should still be on the cold side of center (but in the white). If it is center or higher, there is most likely a problem with the gauge/sender/VS. (Could be a bad thermostat, but I've never seen one fail that way.)

As a side comment, when I tried to calibrate the voltmeter for my Stag (which is basically the same movement as a TR4A temp gauge), I discovered that one of the adjustments was way loose. I could move it just by thumping on the gauge housing. Apparently the rivet that forms the pivot for the adjustment was never staked properly at the factory.
 
Thanks guys - super information as always.

Is a IR thermometer gun accurate enough to take readings to help sort this out as well? They need to be pointed at non-shiny material if memory serves, correct? Measure at rubber neck going to the radiator?
 
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TDSkip, did you check the voltage for the regulator, it should read in the neighbor hood of 10vdc going into the gauge. They go bad and will give readings all over the place. It's in the passenger wheel well up in the right corner.

Wayne
 
tdskip said:
...Is a IR thermometer gun accurate enough to take readings to help sort this out as well? They need to me pointed at non-shiny material...
Click to expand...

That's what I use. I painted a flat black spot on the thermostat housing to point at. Also have a LCD temp strip. Both are near the sending unit for consistency.

TempStrip_zps2739d287.jpg
 
trrdster2000 said:
TDSkip, did you check the voltage for the regulator, it should read in the neighbor hood of 10vdc going into the gauge. They go bad and will give readings all over the place. It's in the passenger wheel well up in the right corner.
Click to expand...
Actually, the original VS will give readings "all over the place" with an ordinary volt meter, as that is how they work. The output switches between 0 and full battery voltage fairly slowly, such that the average is 10 volts. The gauges respond very slowly, so they work on the average.

If you do find the voltage jumping around, chances are that the VS is OK. Not guaranteed, the average could still be something other than 10v, but at least the heater winding and contacts are still working.

However, the solid state aftermarket voltage stabilizers sold by Moss and others do supply a constant 10v. It's actually not too hard to convert a broken original to solid state; but I don't have the link handy on how to do it. Basically you pry the can open, remove the contents, then mount a IC voltage regulator inside, preferably along with a couple of small capacitors. I used a low dropout version, but most people use the venerable LM7810 or equivalent.

PS, here's one article https://www.britishv8.org/articles/mgb-voltage-stabilizer.htm
 
I chased the same problem and it ended up being a bad sending unit.
Charley
 
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