overheating

[jezza80]

hi can any one help i have a 03 1.6 focus zetec se. the problem is it sometimes throws the temp needle to red ive changed the stat flushed radiator but no luck.i have also noticed that the fans seem be running a lot of the time. no loss of coolant or anything drives spot on any help on this would be appreciated could it be CHT sensor. also forgot to mention to bottom hose on the rad after a few mile feels cool and the return pipe back to the coolant resevior is surging coolant back in shouldn't this be a constant flow like a tap when up to normal TEMP 

[Baz_ford_tech]

Could be either a choked radiator or an airlock. How does the bottom of the rad feel??  The rad should be hot all way down.  

[Tdci-Peter]

10 hours ago, jezza80 said:

The problem is it sometimes throws the temp needle to red ive changed the stat flushed radiator but no luck.i have also noticed that the fans seem be running a lot of the time. no loss of coolant or anything drives spot on any help on this would be appreciated could it be CHT sensor. also forgot to mention to bottom hose on the rad after a few mile feels cool and the return pipe back to the coolant resevior is surging coolant back in

If the bottom rad hose stays cool when the engine temp gauge is in the red, then either the thermostat is jamming closed, or the CHT sensor is faulty.

While the thermostat is closed, ie engine is below full operating temp, there will usually be some flow back through one of the small vent pipes to the reservoir. On my Mk2, there are two vent lines, one from the top of the rad, one from the thermostat housing. With the thermostat closed, the water pump pressure across the thermostat may be enough to drive water back to the reservoir through the vent. I think the Mk1 is similar.

Run the engine from cool, up to temperature, feeling the rad top hose. It should stay fairly cool until the thermostat opening temperature (80C to 90C, usually), then quickly get very hot. That is the simplest way to check the thermostat is opening, though it may still be sticking intermittently, from what you describe.

The bottom hose will warm up a bit once water is flowing via the rad, but should not get very hot unless the engine is working really hard without much rad airflow. And you are not very likely to be feeling the hose at that point in time!

If the stat is working, and water return temperature is ok, it is worth checking the wiring to the CHT, and maybe changing it.

[jezza80]

On 12/07/2017 at 10:28 PM, Baz_ford_tech said:

Could be either a choked radiator or an airlock. How does the bottom of the rad feel??  The rad should be hot all way down.  

the rad feels cool thank's

[jezza80]

thanks drained coolant today filled system through heater hose first as ford state drove for 3 mile seemed ok.Fans not running full for long then got home.Now strange thing is when't back out again an hour later only did 1 or so mile then came to slight hill then needle over to red again its baffling me so the next step is CHT sensor