Mini Temp Gauge too high?
Answers:
Check the wire going to the temp sending unit. If it's grounding out, it will cause that problem. Also, disconnect the wire and use a DVOM meter to check the sender. More than likely, the sending unit is bad. Hope this helps.
Master tech 40 yrs.
Faulty thermostat - rare to stick closed, but not unknown. If heater working, blockage in heater matrix unlikely, but could be blockage in main radiator matrix. Only way to test thermostat is to get it out, suspend in saucepan of boiling water and see if it opens - usually easier just to put a new one straight back in.
does your water level drop at all ? on the mini there is a small hose between the water pump and the head called a by pass hose in later models its blanked off but its tricky to see and tricky to fit, id also as suggested check the thermostat see if it opens if you want to test it correctly look on the top and there will be some numbers stamped on there eg 88 this is the temp that it should open, then as suggested put in a pan of water and heat slowly and pop a thermometer in there and watch the temp and the thermostat if it opens at the correct temp thats fine if not then replace, cost about £6 from a motorist shop use new gasket and a smear of sealer on both sides and ensure the aluminium housing is clena where it joins the head or it will leak
sounds like the thermostat is jammed closed, either that or the temperature sender is shorting or fauly, although this would mean that you would be running hot when teh engine is cold
worst case is a blocked or knackered radiator, get it flow tested.
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