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

[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

[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

[steveo3002]

yes i did

[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?

[steveo3002]

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

[steveo3002]

can you tell me where the sensors are please

[steveo3002]

i can get my scanner thingy to display live readings from the head sensor , but without knowing what reading i should expect its no use

im told head sensor feeds the ecu which then tells the fan control to turn on , but id need to know at what xx degrees , its alos suggest the temp gauge is more of an indicator and cant be trusted to show any sort of accuracy ??

Edited by steveo3002 on Friday 17th March 18:32

[steveo3002]

personally i dont think an engine can go from normal to red hot and back again within 10 seconds, so thinking thats an elec glitch

although that doesnt explain why it boiled up in the first place

[steveo3002]

right update if anyones still looking in

driven the car alot and keep stopping to check , at no point does the hoses /rad feel too hot

gauge still shoots from normal to hot and back again in around 10 seconds , seems to happen mostly when going from 70 ish and backing off to 50 , i think its too fast to be a genuine overheat

fan comes on randomly even at speed

i got the machine hooked up and cylinder temp is showing 114 after a long run , hoses felt normal , no fan on , im told fan should come on at 105

does it sound like a duff cylinder head temp sender??

basicly its thinking its hot and its not?

[steveo3002]

thanks...got the head one here and will fit it at the weekend

[steveo3002]

new sensor is in...readings seem a bit random , should it be calibrated or something after fitting?

[steveo3002]

genuine temp sender fitted - still the same

not sure what else to do - couple of threads on the forums saying thiers was the ecu , might try a ebay one out of desperation

http://www.focusfanatics.com/forum/general-technic...

[steveo3002]

second hand ecu does just the same

[steveo3002]

GreenV8S said:

Suggest you buy a thermometer with a remote (wired) sensor that you can position inside the vehicle and see if the top hose temperature is actually varying as your gauge suggests. An ordinary (contact) sensor will read reasonably quickly (tens of seconds) if attacked to metal which is in direct contact with water such as an outlet spigot. Remember to insulate over the outside so that you're only seeing coolant/pipe temp and not an average with air temp.

yes i had thought of that , im reasonbly sure its not actually overheating but peace of mind and all that

trouble is it goes into limp mode/2cyl mode when it thinks its very hot

[steveo3002]

Dogma1978 said:

Have you tried the thermostat as I suggested mate. You've already stated that the cooking system was full of crud. If this is the case the thermostat could be clogged up or at its age it's probably failed. If it's failed in the closed position then the car will over heat. Also would cause the cold pipes after the stat location

it had a new one first job i did on it , in desperation ive knocked the guts out of it and been for a jaunt , as expected its very slow to warm up but ive done about 60 miles tonight with no warnings /overheats , the fresh coolant that came out looked fine , no sludge or bits in it

not sure if that means dud new stat ,massive air lock , or that the gutted stat is giving a partially block rad an easy life