My 2000 focus is overheating when driving fast (40+mph). Its OK when driving slow or idle. I have replaced the following:
1. Radiator
2. Thermostat
3. cylinder head temp sensor
4. timing belt
5. Water pump

The mechanic is 100% certain its not a head gasget issue (he said "you would see coolant in the oil, compression would be effected, oil in the coolant, coolant would be bubbling in the reservoir etc etc ")
There is no sign of a coolant leak anywhere.

When I run Self Diagnostics Mode no DTC codes appear. I even reset the computer!

I checked the two hoses in/out of the radiator and they are at the same temp (after the engine is left idle for a while)

Anyone have any ideas on what it might be?

 

thats a bloody strange one. take it your water levels ok? could it be you radiator is covered up some how so when the engine is under load and producing more heat its not gettin enough air flow to cool it?

 

the water level is fine. There is no blockage in front of the rad. I can drive it at low speed but high RPM and it stayes at the correct temp. It only seems to happen at a high speed - not effected by the engine RPM
It is strange indeed, wonder if the guage is faulty (the self test seems ok though)

 

if its not affected by the rpm then i'd say it must be a faulty gauge or sensor.

 

have you bleed the coolant system? could be and air lock?
have you used the cluster to tell you want the engine temp is?? (this way you know if it is over heating)
hope that helps Matt

 

If you hadn't mentioned that you have already replaced the water pump i would have put money on it being the problem !

Seen quite a few give bother, the plastic impeller breaks away from the pump body and wont pump the water through the engine at higher revs or when out driving on the road, usually alright when at idle and only heats up when driving.

Other than that this sounds like a real strage one, faulty temp sender maybe ?

 

Sorry if I missed something here, but WHY do you think it is overheating ?, ie what is it doing to lead you to this conclusion ?.
Don't under any cicumstances assume the gauge is anything like remotely accurate, could just be a dicky cts(gauge one) if it's the only reason you believe the engine is overheating.
tabetha

 

+1, to add are the cooling fans activating? If it's genuine overheating they should do

Martin

 

Did you find a solution - mine is doing this.

J

 

start it up look under bonnet and look for any coolant coming out from any where whilest giving a few revs of the throttle bodie might be throwin water out under load ive had this happen to one of my cars and it turned out to be this a very tiny hole in a ipe that was throwin water out at pressure when the engines revs are running higher therefore the water pumps throwing the water round at more of a rate causing the pressure to allow it to leak and obviously during idea not doing so allowing the coolant to flow correctly etc. worth a try

 

check the small hose one the top of the termostat make sure its not blocked just a guess pretty sure it lets the air bleed from the system