Temperature Fluctuates In 5Th Gear :-/

[Lofty82]

Hi all

5 weeks ago I had my cambelt and water pump changed on my 54 plate ford focus 1.6 petrol 70k miles. After 2 days the temperature gauge would go into the red, then the engine light would come on and the car would go into limp mode and then cut out!! I took it back to the mechanic who changed the thermostat, and the sender... After having it back several times he eventually stopped the car from going into limp mode and it stopped cutting out. Unfortunately the temperature gauge was still fluctuating but only in 5th gear on a dual carriageway say doing 70-80... He had the car back again and changed the water pump again and fitted a ford thermostat and a ford part sender but the problem still occurs!! It's fine pottering around in 3rd and 4th gear but as soon as it's in 5th gear at a constant speed the temperature gauge shoots from half way to 3/4 and then to nearly in the red!! It seems to only do this if I put my foot down for say 30 seconds, as I ease off after say 5 seconds it drops back to normal. It did this several times tonight on say a 8 mile run up the dual carriageway. Also when I switch the ignition on sometimes it will take 5 seconds for the instruments to kick in and they just wiggle at the start of each dial!! Any advice would be gratefully appreciated, as I and my mechanic have run out of options! There's no airlock and it's been on a diagnostics machine several times. I've googled it and there are loads of forums with the same issue but no one has a fix, I know they are known for the instrument clusters going and that that might be the next step, but my mechanic finds it really weird how it only does this in 5th gear and that everything else is ok. Once again any advice would be gratefully appreciated

[FOCA]

The faster you go, the more throttle/ revs you need, and the higher the load on the engine higher gear = heavier load more power = more heat - simples

so that explains the top gear/ foot down extra heat/ temps but not why the cooling systen is not working properly

it is possible the radiator is blocked, i have heard that additives, like stopleak, can block radiators

how can you be sure their is no airlock? - the coolant could be renewed too

the system pressure could be tested - if the head gasket (combustion chamber) is leaking into the waterjacket (head gaskets can blow in different ways) - it can overpressurize the (coolant) system - this needs to be checked

The drive going onto the waterpump can shear, or the splines strip, the system could be tested to check for circulation

As a temporary measure, next time it overheats try turning the heater up and see if that cools the engine