Cooling problem

I bought a 1999 Fiesta 1.25 Ghia (Zetec engine) with airconditioning. It has done a genuine 22,000 miles. I was aware that the engine wasn’t heating fully, as it felt cool to the touch and the temperature gauge would rise to midway when left to idle for long enough, but then drop back down when driving. I thought an easy fix would be to replace the thermostat. However, when I removed the thermostat housing, I found only the flange of the old thermostat – this was just a means of holding the gasket in place, so the whole workings of the thermostat had been cut away. Effectively, there was no thermostat!

I made enquiries and found that the previous owner had the timing belt replaced at about 20,000 miles and a new water pump and thermostat housing was fitted at this time. I’ve spoken with the garage and they said that, a few days after the work, the car was overheating, so they removed the thermostat.

I fitted a new thermostat and gasket. All was well for about four miles of motorway driving, then the temperature gauge would rise to ‘Max’ and drop back to midway, rise to ‘Max’ and drop back to midway. I think this was the cooling fan switching in and out, affecting the coolant temperature.

I could hear gurgling from the block and the coolant was expanding back into the coolant bottle with the bottom hose staying cold. It seems as if the thermostat does not open. I took out the thermostat and tested it, but it works as it should. I back-flushed the block and the radiator to ensure there were no blockages and the system seems fine. In fact, I’ve never seen such clean water run through an engine!

I’ve now reverted to the ‘doctored’ thermostat to keep the car running – while the engine runs cooler than it should with this arrangement, both the top and bottom hoses feel warm.

In a nutshell, I have a new water pump, thermostat housing and thermostat. The engine heats up, but the thermostat doesn’t seem to open (based on the top hose heating and the bottom hose staying stone cold). The radiator and engine block are not blocked (based on running water through with a garden hose). What am I missing? Could it be a head gasket problem – but, if it was, shouldn’t the thermostat open anyway? Tim Lynch As you have eliminated the thermostat as being faulty, I suspect that the replacement water pump may be the problem. I have come to this conclusion because, as far as we know, there were no issues prior to the water pump replacement. The water pump was not replaced because of a cooling problem, but as a preventive measure during the cambelt change. As the problem occurred after this, I suspect that the impeller on the water pump may be insecure on the shaft and not turning efficiently. This would result in the poor flow you have, which mistakenly appears to be a thermostat problem. My first move would be to remove, check and possibly replace the water pump.

I do not suspect a head gasket problem as this would pressurise the cooling system and it would most likely still overheat, even without a thermostat. However, another possible scenario is that the radiator is partially blocked and preventing sufficient flow through the system. Using a radiator flush may help, but as you have said the water in the cooling system is very clean, this is less likely.