Knowledge Base - Info:- Test for Faulty Thermostat / Gauge Sensor

A test you can do is start the engine from ice cold and let it idle. Have the front bonnet up and feel the coolant pipe that disappears through the bulkhead to the radiator. If it warms up slowly, getting hotter and hotter, your thermostat is fully or partially open all the time. You would expect the pipe to stay cool then all of a sudden become hot as the hot coolant is passed through the radiator when the thermostat opens.

With the engine hot (electric radiator fan cutting in), jump in and drive on a nice open road at speed. If the coolant gauge drops to cold from mid way, you will need a new thermostat.

If the gauge never rises to the normal half way mark whilst stationary (again with the radiator fan cutting in), your gauge is not working. This is normally caused by a sensor fault or a wiring problem (bad connection between the sensor and it's connector plug).

You can test the gauge operation by disconnecting the sensors plug and connecting the wire to earth. This should make the gauge shoot to hot, confirming correct operation of the gauge itself.

Peter Jones.

Copyright © by MR2 Owners Club All Right Reserved.


Created : 2011-10-05 15:42:50, Last Modified : 2011-10-05 15:42:50

Technical Disclaimer 

The MR2 Owners Club and its respective owners, editors and contributors make no representations about the suitability of the information contained in the documents, materials and related graphics published on  

By using this site, you hold the site and it's affiliates not legally responsible for any damages due to advice given here. This site and it's affiliates takes no responsibility for consequences of any actions that arise from advice given. Any opinion is given with information provided by you and can not be taken as absolute.

All repairs should be undertaken by a competent and qualified technician. By using this site, you understand and agree that all advice given and followed are at your own risk and do not hold this site or it's affiliates responsible for any damages.