Coolant loss/Overheating - Fiesta 1.25 2010

[mg-tart]

Hi All,

Not so quick question (which may not result in a quick answer !!)

Fiesta (2010 1242cc Edge 82 - ie: not zetec) recently came up with red warning light on dash (no temp gauge)

Had been long hi-speed run coming to standstill in traffic.

Lost around 1 1/2 lt coolant - topped up and bled it.

It now runs fine for 5 minutes or so idling then the coolant boils and expands and tries to escape. Fan doesn't come on.

Have fiddled about a bit (as much as possible without draining and changing items) and as soon as I dump the heat through the cabin by turning on the hot air and cabin fan to max the system settles down and the water ceases it's escapology attempt. (Obviously not ideal long term if the recent spell of good weather continues)

Is this a sign of a jammed thermostat, a faulty heater valve or a knackered temp sensor........ or a combination of two or more items?

If it was yours... where would you go first?

(Bit surprised the fan didnt come on to be honest)

Cheers

Andy 

[Neb_engineer]

do you have an OBD interface you can plug in?

[mg-tart]

2 hours ago, Neb_engineer said:

do you have an OBD interface you can plug in?

Hi,

Only a basic one which shows nothing doing.

No codes held and no EML on.

[Luke4efc]

It seems me like its more of a fan/temperature sensor issue. Do you have air con? If the fan comes on when you press the A/C on then you can rule a lot of the fan stuff out. If you don't have A/C then perhaps using the live data on Forscan to measure the engine temperature may be your best bet.

I wouldn't say it's the thermostat stuck shut as the engine temperature doesn't climb when you use the cabin heater on full blast (and presumably it's fine when you're going at speed?).

[mg-tart]

10 hours ago, Luke4efc said:

It seems me like its more of a fan/temperature sensor issue. Do you have air con? If the fan comes on when you press the A/C on then you can rule a lot of the fan stuff out. If you don't have A/C then perhaps using the live data on Forscan to measure the engine temperature may be your best bet.

I wouldn't say it's the thermostat stuck shut as the engine temperature doesn't climb when you use the cabin heater on full blast (and presumably it's fine when you're going at speed?).

Hi,

Ok , so the fan doesn't come on when you press the AC button so presume there is a burnt relay somewhere. 

Car is fine when driving.

coolant issue settles down as soon as the cabin temp dial is set to hot and cabin fan is turned on as this is obviously drawing the heat out of the system where the normal radiator fan is presumably not doing its job.

Thx

[Luke4efc]

5 hours ago, mg-tart said:

so presume there is a burnt relay somewhere

That would be my next suggestion.

[mg-tart]

On 7/29/2021 at 4:19 PM, Luke4efc said:

That would be my next suggestion.

Hmmm - Checked all the appropriate relays and changed it out for known good one - no difference. (there's only 1 relay - 40A in engine compartment - Where the "engine cooling fan relay" is  noted to be (R7) there are no connections) Nothing noted for the passenger compartment fuse block

It hasn't overheated as such but I didn't have time left to leave it long enough but when the AC is switched on there is nothing from the engine fan - is it an automatic thing that this occurs when you switch the AC on?.

Appreciate your help.

Andy