Does my newly-rebuilt 1999 Ford Focus have a thermostat fault?

I have recently rebuilt a 1999 Ford Focus 1.6 SE silver top engine, which runs very nicely. When the thermostat opens, the bottom hose gets nice and hot, but after a higher speed run the hose goes very cool. If I then wait and let her tick over for a few minutes, the bottom hose gets very hot again. I disconnected the radiator fan connector, but nothing has changed. She has a new water pump, Ford thermostat, no leaks, and the matrix gets hot. From cold in the morning, the thermostat is fully open within eight minutes, and both heater pipes get warm straight away. The temperature gauge never goes past normal and the radiator fan kicks in for a short while and then goes off. I guess there might be an air pocket, but I don't want to pay out for the heater return to top hose kit unless I really have to. Does this mod really work? My local Ford dealer wanted £76 for the 74 degree thermostat. I haven't checked the rad for a blockage as it didn't play up before I stripped her.

Asked on 26 July 2010 by bendee

Answered by Alan Ross

Not really sure that you have a problem. As you say, everything works ok, the engine runs fine and temperature is ok. It's worth remembering that on high speed runs, the air flow through the radiator matrix is substantial and, as such, will cool the water temp very easily. However, when at idle, no air flow is going through the radiator unless the radiator fan kicks in, and as such the water temperature will increase. Considering all the work that you have done on the engine, it may be prudent to make sure that the rad is flushed out anyway so ensuring no problems.

Tags: cooling system thermostats cooling fan technical issues

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