Coolant gauge

Q After a long run of nine miles or more, the temperature gauge in my 2010 VW Golf 2.0 diesel with a DSG gearbox sits on the bottom. By jiggling the heater, the temperature gauge slowly rises – the heater controls seem to be some form of semi-automatic half climate and do not seem to be connected to anything! I have replaced the sender in the top hose, but cannot see any more senders.

I acquired the car seven months ago with 70,000 miles on the clock, at which point I changed the cambelt, DSG fluid, etc. However, when first getting into the car, with my foot on the brake and the gearbox in neutral, it will not rev above 2500rpm no matter what I do. On the move, it’s fine, even at motorway speeds. Am I in charge of it or is it in charge of me?

Trevor Harris A Your vehicle has two temperature sensors: G83, which is the one you have changed in the top hose, and G62. The latter sensor is less accessible and fitted below the coolant outlet at the back of the cylinder-head. If you have access to a scanner, read off the live data to ensure the sensor is faulty. The electronic temperature controls on the climate control system should not affect the temperature gauge reading.

Another possibility is that the thermostat is remaining open and preventing the engine from warming up. The thermostat on your Golf is located within a 4/2-way valve. This is quite a complex unit to replace. By feeling the temperature of the top and bottom hoses, it should be possible to determine if the thermostat is operating. The hose should remain cold until the engine is fully up to temperature and the thermostat should then open, allowing hot coolant to circulate.

It should also be noted that, with the DSG gearbox, the gearbox oil cooler system also has a thermostat.

Regarding your second problem, when the vehicle is stationary the engine is limited by the ECU. As you will know it is not good practice to rev an engine which has no load on it. For this reason, the software will prevent the involuntary revving of the engine when stationary to prevent damage.

I then received this reply

The mechanic at my local garage changed the engine thermostat above the alternator, but the problem was still present. We checked and tested all the sensors and they were all working fine. After further investigation, it turned out to be the DSG thermostat which was to blame. A new part from VW for £111 cured the problem. The part is a series of small-bore pipes and one large one with the thermostat running in between.

Trevor Harris