Dash showing engine temp is realy hot! NOW SOLVED!

I think it's the viscous unit on the fan as you said when you drove quicker it cooled down, which it would with the airflow over it.

I would do as has been suggested with the cable ties to lock it up to see if it is that before taking anything else apart or buying new parts unnecessarily.

It's a process of elimination.

Kirkynut

If it was me I would not "lock" the fan up as all you are going to do is over cool the engine and just mask the problem, all of the syptoms you are saying point to a sticking thermostat. I have have not seen a fan to start and stop work it's a very simple bit of kit when they fail they normly lock up solid or just turn very slowly.

If the Thermostat is stuck shut no coolant will be passing through the rad and it would stay hot all the time and would not cool down. Been there, done that, had the warped head as a result.

Locking the fan will cool it more and if the problem goes it will have been the fan that was at fault. The temperature goes down when driving due to the air forced through the rad by moving.

If a Thermostat is stuck, it's stuck and the symptoms will remain as overheating.

They are only under £10 and easy to change, so perhaps change it anyway. Then boil it in your Mrs favourite saucepan to see if it opens!

You'll know it has fresh anti freeze in it for this winter then too as you'll have to drain that.

Kirkynut

Thanks again guys
As kirkynut said if it was stuck shut the engine would overheat and stay hot, wouldnt it? Does the viscous fan only kick in when the engine starts to get to hot and so helps to cool it down? The temp reading stays fine on a short journey but only goes up and down when on a longer trip. It doesnt stay in one place if you kno what i mean.
So this cable tie trick, do i tie the viscous fan to the main fan?
I have just put fresh coolant in do you think if i drained it, to fit a new thermostat, i could re-use it? Or is it best to put new in again. Its only been in a week or so.

Nobby

To check the viscous unit:

With a cold engine, grab the fan blades and see if there is side to side play or a rattle = gone
Try and turn the fan by hand. If it feels stiff but will turn it is ok.

Most likely, the fan will feel loose and spin easily = gone.

Go for a drive with the window open. When you first drive off the fan should roar like a vacuum cleaner when you rev the engine from cold, then the noise disappears when hot.

(No idea why this happens, it is the exact opposite of what you would expect, possibly the fluid has to warm up before it can start working properly)

I may be able to help you with this Process of elimination
Ok this is what to do :blink: First you can check your thermostat by removing it from your car and putting it into a pan and then pour boiling water from a kettle on to it. If it does not do anything then Its buggered if you see it pop or move then its fine and you can put it back in The thermostat activates at around 83 degrees so boiling water will trigger it.
You may have an air lock in your cooling system.. seek advice as to how to get the air out...
Answer these questions
1 Are you losing water only slighty
2 And can you see tiny dots in your oil on your dip stick.