Faulty thermostat or guage?

OK, a quick summary of the events leading up to the apparent problem with my cars cooling system.
Noticed there was a leak on the cooling system the other week, turned out to
be a crack in the thermostat housing. So replaced the housing, seals and thermostat.
Took it for a test spin after refilling, noticed both cooling fans were coming on, despite the fact the bottom radiator hose coming from the thermostat was still cold and the temp gauge was still "normal".
Assumed it was an airlock, so stopped, gently turned the filler cap on the expansion tank to release the pressure. There was a lot of bubbling, which I thought meant it was just air pockets escaping. After I restarted all seemed well.
However, I've noticed that the cooling fans keep coming on when I'm driving around, even though the temp gauge says the temperature is normal and the bottom radiator hose is cold. When I stop and release the pressure on the expansion tank, there's a lot of bubbling water coming from the hose that feeds back into the tank from the top of the engine block and the fans stop for a while.
Tried flushing the radiator through to see if there was a problem there, flushed through fine.
If I didn't know better I'd say it was a combination of faulty thermostat and temperature gauge not giving the correct reading.
Any other suggestions what the problem might be before having to take the thermostat back out for testing? Don't really want to do that if I don't have to as its an absolute swine to get to, being sandwiched between the alternator and air-con cooling pump, meaning a major strip down. Wouldn't have thought it would have been the thermostat with it being brand new, but don;t know what else it could be? Engine is supposed to run at 82 degrees and bought the correct stat.
The car is a V reg Ford focus, 1.6 petrol, with a zetec engine. UK model.
Any suggestions gratefully appreciated.
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Simon (Dark Angel)
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On Sat, 15 Jun 2013 09:31:47 +0100, "Simon T"

Looks like the new thermostat is bad or installed wrong. Remove it to see if circulation is restored.

The bubbling may be exhaust gas getting into the coolant. The engine may have over heated, warping the head. If so you need a top end rebuild (ouch!) If the head is warped it may allow coolant to get in the oil and ruin the main bearings, requiring a complete engine rebuild. (ouch!) Watch for signs of water in the oil. It may turn milky white if water is in it.

Sure looks like it from here. Could the wire to the temperature sensor got pulled of while you were working on the engine? If the wiring is ok, test or replace the sensor.
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"Peter Piper" wrote in message

I'll double check the oil, but it was alright the other day and doesn't seem to be losing water.
Been asking elsewhere, seems the gauges on these cars aren't accurate, which would explain the gauge problem. Looks like its either the new stat is faulty or there's a problem with the water pump, which I will be testing shortly.
The thing that really pisses me off is that my local ford dealer don't keep the parts in stock, they have to send out for them, so I roll up at 830 to order them, then have to come back at lunch time to pick them up. Whereas if they had them there I could have the car finished by mid-morning.
Anyway, thanks for trying to help!
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If the A/C is on, the fans will run no matter what the coolant temp is. Make sure the control is set to Off to be absolutely certain that the A/C is off.
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Quick update for anyone following the thread.
Removed the stat and tested it, opened up fine after dropping it into a pan of boiling water.
Coolant pump spun freely and could feel the impellors turning inside when I spun it, so knew the pump was working.
I'd flushed the rad through with a hosepipe the other day, so was reasonably sure it wasn't a blockage there either.
Anyway, someone suggested getting it up to temperature, then running it without the cap on to clear any air locks. Did this for a while and could feel the bottom hose on the radiator getting warm, so it looked like the water was flowing.
Anyway, put the cap back on and took it for a spin, both rad hoses were warm and the cooling fans didn't come on, so I think that's done the trick.
Must have been an airlock (unless there's something else wrong that I haven't discovered yet In which case, I'll be posting again shortly).
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Simon (Dark Angel)
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On Mon, 17 Jun 2013 11:36:50 +0100, "Simon T"

Thanks for the update.
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