79 Esprit S2 engine cooling issue

[Greg Henderson]

Here’s my issue. After I start the car the temp gauge slowly climbs and pegs out at 140. Takes about 10 minutes for this to happen. I replaced the thermostat and burped the system. While burping for 15 minutes the temp gauge stayed around 95 degrees. Took a drive and all was normal until 30 minutes in when the gauge rose to 140 and stayed there. I burped the system again but it didn't help. Any ides what could be going on?

[s1guy]

Fans coming on ? Otter switch could be going bad. Or bad.

Edited August 22, 2020 by s1guy

[Lotusfab]

The first thing to do is test the temperature gauge is correct. Take the sender out and put it in boiling water with a thermometer. Let it cool and compare the gauge against the actual temperature. If its wrong check the contacts are good, power to it is ok (voltage regulator) and finally recalibrate the gauge.
If its correct there is a genuine problem with the cooling system. 140 is very very hot, so probably a gauge problem. I had exactly this and it was just the gauge over reading. I find it hard to believe it can reach 140 degrees in 10 mins, unless of course there are other symptoms? 

[marode]

Air bubble? Have you drained your cooling sytem recently? I´ve had similar issues before with my S2 after I had refilled the cooling system. Lift the car at the rear or park it somewhere with it´s nose down and keep it running for a few minutes. Try to get rid of air bubbles in the cooling system.  Water doesn´t get to 140° within 10 minutes I´d say.

Edited October 21, 2020 by marode