Overheating

Q My friend has coolant issues with a 2013 Chevrolet Orlando 2.0 turbodiesel. The problem is that it overheats when you drive it on the motorway, but in and around the city it does not overheat at all.

When it overheats on a motorway trip the two fans on the radiator starts operating like crazy and continue until it starts to cool down. He has changed the thermostat, and changed the radiator for the engine. Also he checked to see if the coolant being returned to the expansion tank, which it was. That means that the water pump is working OK.

I also told him that when it starts to overheat, to keep his eye on the engine temp gauge and bring up the rpm to between 2000-3000 and look to see will the gauge go back to normal.

He told me he couldn't, because you can’t carry out this check on a motorway with other cars flying past. Also you can’t pull up on the motorway for no good reason, and by the time he comes off the motorway it seems to be fine.

Since he changed the radiator, it has improved a bit. If you leave the rad cap off the expansion bottle when it is running there are no bubbles in the header tank, or no pressure in the bottle.

I would appreciate any help you can give me to sort out this problem.

Gerry Kelly A Having changed the radiator and the thermostat – and checked for any bubbles in the cooling system as well as checking the flow and the operation of the water pump, I would say that the cooling system has been fully checked and would not appear to be the problem.

There are two further reasons that can cause the overheating of a diesel engine under the conditions described.

This may be either a DPF or exhaust blockage, which will cause a resistance to the escaping exhaust gasses and an increase in the running temperature, or a problem within the injection system.

If the injectors are not operating correctly then the engine when operating at motorway speeds will need to work harder to maintain the output and this can cause the engine to overheat.

If the problem were a blocked exhaust or DPF I would expect a code to have been triggered, but it would do no harm to carry out a pressure test of the system, to ensure that the pressure build up is not excessive. Remembering that any slight overpressure when testing stationary will be multiplied at motorway speeds.

If no problems can be found with the exhaust or DPF, then it would be worth getting the injection system checked – removing and cleaning/checking the injectors may be a wise move.