Thermostat

[Ricky Ellam]

Hi all, I’m a novice mechanic and have owned my stag many years but one thing is making me nervous when I go on a long drive is my thermostat reading.
it touches red all the time but doesn’t overheat, I’ve changed the gauge and added an electric fan and a bigger radiator but it doesn’t make any difference to the reading on the gauge.
should I change the thermostat and if so which brand should I use, my car is a 1977 with original engine which has been rebuilt in 1993 but has only done 6000 miles, yes embarrassing or what, but I am now semi retired and I intend to use it more now.

any recommendations please

regards

Ricky

[sujitroy]

A couple of things, is your car an auto or manual? I find my autos temp gauge goes all over the place because the RPM is way higher at speed
The temp gauge runs off the voltage stabilizer and so does the fuel gauge. Does the fuel gauge read right? I'm in USA, only after adding a rad. cowl, did my temp. gauge read lower. I have a Hart Super Gill rad.
Sujit

[Ricky Ellam]

Hi , thanks the reply mine is a manual with overdrive, my fuel gauge reads ok.
the temp gauge needle gets to red within 5 mins of driving and stays there the whole journey. I did 80 miles on country roads lots of gearing changes and with no problems

[Pete 21]

Hi- assuming it is an issue in the cooling system that’s causing you to run hot I’d suggest check that you have the right thermostat first. There’s a difference between the mk1 and mk2 versions that impacts on water flow. I had some over heating problems with my 74 mk2 that perplexed me for some time but ultimately turned out to be that I had a mk1 thermostat in place. Changing it to mk2 sorted and runs nicely just below mid-dial now which is great…although tinge of frustration that I didn’t sort something so easy earlier.

[sujitroy]

When you got the car, where did the gauge needle read? Is this something recently happened?
Sujit

[NeilR]

You say you changed the guage, but did you change the sender as well ?

[Wisey]

Drop your coolant level, remove coolant sensor. Make extension leads for signal and earth. Place extended coolant sensor in boiling water (kettle/saucepan). Turn on ignition, make a note of the temperature gauge reading.
This is probably the only reading you will ever need to read correctly (100 deg c). Hopefully it will be around mid point on your gauge. If not, try a new sensor.

[MikeParker]

Worth buying an infra-red thermometer. When your gauge is reading red, point the thermometer at inlet tube at the top of the radiator. It should read about 78-85 C. If it does, the there is a problem with your temp sensor or gauge. If it is reading 95-105 C then you have a problem with your thermostat.

[022Dave]

Ricky,

Does the car 'smell' hot when the gauge is near the red? Normally an overheating engine smells hot & bothered, but 5 minutes seems a bit short to get to that stage unless there's a blockage. If that's the case, start looking for coolant level or flow problems, blocked radiator fins, etc. Does your fuel gauge also read high? If so, that could point to the 10v voltage regulator behind the speedo misbehaving. If it's neither of those, and you decide to go shopping for a new temperature sender, get one from LD Parts; they are known to be of good quality.

Dave

[Ricky Ellam]

Thanks everyone, I have some checks to do tomorrow.

[Goldstar]

I had a duff temp sender which read hot instantly so I'm not sure it will be the sender although, of course, it might be. My money is on a blockage/reduced efficiency somewhere, most likely the radiator. I know it's possibly not the weather for it at the moment but what happens to the air in the cabin when you put it to full hot? Is is hot (it should be) or just warm?