Thermostat and temp gauge faulty?
 

OK, got a V-reg Ford Focus 1.6 Petrol Zetec Engine.

had to replace the thermostat housing on my car the other week as it had a crack in it and was leaking. Got new seals and replaced the thermostat at the same time.

However, I don't think the new thermostat is working. The hose going from the stat to the bottom of the radiator is always cold, whereas all the other hoses are hot. The cooling fans will start running, even though there doesn't appear to be anything flowing through the radiator and theres water bubbling back into the expansion tank from the hose that goes from the top of the engine block .

The odd thing is though, the gauge on the dashboard shows the temperature as "normal"?

When I first refilled it, I had assumed it was just an airlock. I had to replace the stat a few years back and found that by releasing the cap slowly after it had reached temperature released the air and the cooling system worked fine after that. However, this time, having done this several times now, the problem is persisting.

So, any suggestions as to what else might be causing this before I start stripping the engine down again to test the stat? I would have thought being brand new this wouldn't have happened, but can't think of what else it might be and the thermostat housing is a right swine to get to, being sandwiched between the alternator and air-con pump.:(

Also, any ideas why the gauge on the dash still says the temp is "normal" when the radiator cooling fans are going full belt?

Thanks in advance.

They should self bleed any trapped air but with it running give the hoses a good hard pump with your hand, that can help get any trapped air shifting. Sometimes there is a bleed screw on top of the water pump, see if this is the case.

Tried giving the hoses a good squeeze several times, changed the stat and housing last Tuesday, would have thought any airlocks would have made their way up to the expansion tank by now.

Don't suppose it could be the water pump by any chance?

Also, any idea why if the car is getting a bit hot, why the temp guage isn't showing it? :confused:

the temp guages on a focus are totally innacurate if you watch the live data readings on a proper scan guage you can watch the temperature rise from 80-120 degrees and the cars guage will never move from the middle. my guess is waterpump, remove one of the return pipes from the expansion tank. you should have a steady return of water coming out of the pipe when running if the waterpump is ok

Thanks for the advice, I will consult the Haynes manual again and have a tinker with the water pump hoses then.

Right, well just dismantled the car again, checked the thermostat by placing it in a pan of boiling water. Opened up fine.

Spun the water pump, rotating freely and when I feel inside, I can feel the internal wheel going round, so don't know what the problem is :(

Quick update, think I've sorted it.

Reckon it probably was an airlock, I got the car up to temp, turned it off then carefully removed the cap from the expansion tank, then restarted.

Ran it without the cap for a few minutes, after a while I could feel both the radiator hoses getting warm, indicating that the water was flowing.

Replaced the cap and went for a spin, both hoses stayed warm, hot water wasn't bubbling back into the expansion tank and the cooling fans didn't come on after just a couple of miles.

So, fingers crossed, looks like its sorted then.