Erratic gauge
I recently came upon an issue that has me, and others, stumped. The car in question is a 1999 Peugeot 206 petrol that has covered about
135,000 miles. It's driven around 10,00012,000 miles annually and is starting and running really well.
However, there’s an intermittent fault with the temperature gauge. When the car is started in the morning, it is driven around two to three miles, before the needle of the temperature gauge comes to rest on the halfway stage of the dial at a reading of 90°. On some occasions – usually after the car has been started from cold – the temperature gauge will rise in the normal way. The needle will be in the centre of the gauge after travelling say two or three miles. Then, in just a few seconds, the needle will travel up into the red zone of the temperature gauge, accompanied byt a warning light and the 'STOP' message. If you turn off the engine, wait 10-15 seconds, then re-start the engine, the car will run perfectly until the next time this occurs – and it could be a month before the issue reappears.
The engine is not overheating and a new, genuine Peugeot temperature sensor has been fitted, along with a new thermostat. The system has been checked to ensure there is no air lock. The coolant has been changed and is clean. We have also checked that coolant is being pumped around the cooling/heating system. When the car is started and left ticking over for, say, 15 minutes, the radiator fan cuts in and operates normally. The wiring has been examined and nothing amiss can be seen. Nor is there any evidence of kinks in the water hoses. A diagnostic scan has been carried out, but no faults are stored.
There is no trace of oil in the expansion header tank, and no symptoms of water mixing with the oil. The rubber seal on the filler of the expansion tank is good. The control unit for this car is a Marelli.
Have you ever come across this problem before? All checks show nothing to be amiss, but what is baffling is the short amount of time it takes the needle to travel from 'normal' up in to the red zone.
Michael Carty
Given the steps you have taken to resolve the fault – which are exactly what I would have recommended, such as changing the sender and thermostat for genuine units – I would suspect that the problem does not lie directly with the cooling system, but is an electrical fault.
The most likely scenario is that one of the engine earth straps has failed, so I would check these first, paying particular attention to the earth strap attached to the gearbox. I would also inspect the earth connections on the dash and the multi-plugs on the main wiring harness. It is also possible that a short circuit in the dash assembly may be causing the gauge to read incorrectly.
Finally, check the relays for the cooling fans, which are located in a box in front of the radiator. These are susceptible to corrosion damage and can also cause the symptoms you have.