Ford Focus Mk 1 Coolant Issues

Hi everyone,

Was wondering if anyone might be able to help. My beloved 2003 Mark 1 Focus (1.6 SE 16v) which has never had any problems before has been having an overheating problem that has really stumped me. Sorry its a bit long but I've done a few things so far.

Here are the symptoms:

The temperature gauge which used to run bang in the middle of the range is very fractionally above that (a few degrees to the right of vertical). Also, intermittently (getting more frequent though) the temperature goes from this level to the red in a matter of 5 seconds or so. It often stays there for up to a minute or so, then drops down to its "baseline" which is just to the right of vertical. Sometimes, if it stays in the red for long enough the engine management light comes on and sometimes another orange warning light comes on that puts on some kind of rev-limiter, or maybe the car drops down to running off two cylinders.

Oddly, this problem only happens when driving reasonably fast- I can't reproduce it on the drive at home. Doesn't seem to happen at all below 30mph. It doesn't seem particularly related to revs either- more related to engine load generally.

So far I've done a few things:

1. Checked the oil colour to look for evidence of cylinder head gasket failure. No sign of discolouration and no sign of white smoke from the exhaust so I guess this is unlikely and otherwise car is running like a dream.

2. Checked for signs of coolant loss. Doesn't look like it to me- level not dropping at all.

3. Checked Cylinder Head Temperature sensor and replaced it (twice), the second time with a Ford part.Checked wiring to this which seems ok. Moving wires does not reproduce problem so unlikely connection problem I think.

4. Replaced thermostat housing and thermostat which controls flow through radiator

5. Drained and flushed coolant system twice. First time, problem seemed to improve but not go away. Second time, problem seemed to worsen (though not sure if it was worsening anyway !)

6. Refilled with correct mix of coolant in the recommended way to reduce chance of air locks (filled via heater hose which connects to engine until coolant comes out of engine, then topped up via expansion tank.

7. Checked the engine temperature in diagnostic mode on dashboard- temperature seems to run from around 80-105 degees C driving around but sometimes under load it hits 114-115 and that is usually the point where the needle goes into the red. The needle seems to be a little to the left of centre at around 100 degrees, but at the red when around 115 degrees C, which is telling me that it doesn't take much for the car to go from its operating temperature to overheated.

8. Squeezed all pipes to expel any air- no sign of any bubbling out of expansion tank pipes.

9. I've sent the whole instrument cluster for checking/calibration to ensure no issue with the temp gauge but this fixed nothing (and I was £100 lighter).

10 Removed both air bleed pipes that go to the coolant expansion tank (one from the radiator, one from the engine block) to ensure they are patent and flushed them through with water- no obvious problem.

I can't work out if the radiator is working or not. Sometimes, despite apparently overheating the radiator is cold thoughout which to me suggests no flow. Other times I have driven and made the car go hot then pulled over and found the radiator cold, but then when stationary it has gone hot when the car was at standstill which suggests to me that the thermostat has opened and there is flow through it.

So, I'm at the point of either getting rid of the car, or otherwise maybe replacing the radiator and water pump in one go but I'm not convinced with the above that there is any problem with these. I see talk on some of the forums of air locks but I don't understand why that should have suddenly appeared- this problem didn't start after someone fiddled with the coolant system. I wondered if it might be the water pump failing slightly and not pumping quite fast enough so the car is running a little hot generally, and occasionally under load the temperature goes up by 10 degrees C or so and that makes it overheat.

Any advice at all is appreciated please ! Thanks