help with focus overheat problems

[steveo3002]

mk1 1600 petrol focus , had the dash lights come on yesterday on the motorway , luckily dived down a slip road almost straight away and switched off

the coolant tank was full the cap and spiting out coolant , after it cooled it had lost around half an inch or so

got towed home , and pulled it apart thermostat works in a hot saucepan, water pump impeller isnt lose /damaged

refilled it and ran it up again , seems the engine gets hot and the fan comes on after a normal amount of time yet the coolant tank and hoses are still cold , the passneger side rad hose was warm

so in a nutshell...engine hot, rad cold , heater works fine

[stevieturbo]

ensure water pump works, ensure no air locks, ensure rad not blocked...etc.etc

[S0 What]

Did you remove the water pump to check the impellar?
check the small bore return pipe to the header tanik, if they block you loose circulation ?

[GreenV8S]

If the coolant tank is staying cold then you probably have a blockage. This could easily prevent the system from degassing so you could have built up an air lock. Once that finds its way to the radiator it'll cripple the cooling system. It would also prevent the system from filling properly if you needed to top it up after your overheating episode.

[M32Guy]

I'd check the coolant tank. There's a small hole that links the two internal chambers that always gets blocked. Looks like there's coolant buy there really isn't as it's the second chamber that supplies the engine

[steveo3002]

small 90 deg elbow on the back of the head that connects to the small bore hose to the header tank was blocked or at least partially blocked

its all getting hot like it should now , driven it around town for an hour and no mishap's , will keep an eye on it

one strange thing though , the temp gauge shot from normal to max instantly then back again after say 5-10 seconds , it did this a few times , too fast to be a true reading ,more like an electrical glitch

[GreenV8S]

steveo3002 said:

one strange thing though , the temp gauge shot from normal to max instantly then back again after say 5-10 seconds , it did this a few times , too fast to be a true reading ,more like an electrical glitch

That's a symptom of air in the system.

[Dogma1978]

What's the history regarding the car and coolant. Is it serviced well if full of water. If so it needs a good flush and hope for the best

[Dogma1978]

What's the history regarding the car and coolant. Is it serviced well if full of water. If so it needs a good flush and hope Nothing's rotted away 👍🏻

Edited by Dogma1978 on Thursday 16th March 03:22

[steveo3002]

coolant didnt look amazing , has new coolant and new rad cap now

seems ok around town and local trips , need to take it on a longer high speed run and see what happens

[Dogma1978]

Did you flush it though before adding the new coolant

[steveo3002]

yes i did

[Dogma1978]

Nice one mate. Fingers crossed it's fixed 👍🏻

[steveo3002]

its still randomly shooting the temp gauge from normal to red for a couple of seconds then back like its a elec problem

ive got a scanner jobbie but i dont really know what im doing , i can watch the cly head temp sensors reading raise which im told in turn is what triggers the rad fan , but unsure at what temp it should trigger at?

[Mignon]

If the coolant temp sensor is not sitting completely immersed in water because of underfilling or an air lock then it can't actually register a proper temperature. In fact it's possible for the engine to be melting and the temp sensor to register stone cold. Random fluctuations in the gauge can be because an air lock "burps" its way free letting some water to the gauge for a minute (temp goes sky high if water really is that hot) and then air builds up again and gauge drops back.

[steveo3002]

im told its all done by a sender in the head ...actualy in the metal so doesnt contact coolant at all

[Mignon]

You've been told wrong.

[steveo3002]

can you tell me where the sensors are please

[Mignon]

Hmmm, google does seem to think some Focus models didn't have a temp sensor actually in the coolant itself which is highly unusual IME. I guess you'll need to check for your car's actual VIN number.

[GreenV8S]

It seems strange not to have the coolant temp sensor immersed in coolant, but I don't know that engine. The coolant temp sensor is almost certainly a thermistor which is wired into a voltage divider circuit within the ECU. With this type you can see what the sensor reading it by measuring the voltage across the sensor while it is connected to the ECU, or by measuring the resistance across the sensor while it is disconnected. You could use either approach to find whether the sensor is actually reporting the wide temperature swings your gauge shows. (Doing it while connected would be slightly preferable since it would avoid causing fault codes at the ECU.)