overheating TF

Hi all, I thought I'd ask here as I'm stuck. The car's a 2003 1.8 pre PRT.

My car overheats when the heater is set to cold, so far it's had a new radiator, 3 thermostats, water pump & head gasket with a new head for an unrelated problem.

I ran the car for a while without a stat fitted & it never once overheated although the temperature plummets when driving along at decent speeds, I was even sat in standstill traffic for an hour & the gauge didn't move from the normal position.

The rad & engine fans both work properly.

Today I fitted yet another stat & the problem came back, cold heater = overheating but moving the heater to hot the temps drop back to normal.

The radiator seems to be warming up properly & both under floor pipes are heating up.

When I fitted the stat today I checked the heater bypass jiggle valve & there's nothing inside, just a tube/washer thing with 3 holes in, is this normal & could this be causing the problem?

I'm getting to the point of calling it a day now & I really don't want to but I don't know what else to do.

On the upside I can change a stat in 25 minutes now

Hi Daz and welcome to the forum.

After you have completed the jobs you have done did you bleed the coolant system from all three bleed points with the heater set to high?. Bleeding these engines can be a right pain. If you can raise the rear of the car a bit this may also help the bleeding process. Don't give up and if you are still having problems give a one of the mobile mechanics a call.


:beer: :beer: Steve

cant comment on the jiggle valve.....have you replaced the expansion tank cap....has these can be a common failure has the preasure in the system has to be maintained

stevew wrote: Hi Daz and welcome to the forum.

After you have completed the jobs you have done did you bleed the coolant system from all three bleed points with the heater set to high?. Bleeding these engines can be a right pain. If you can raise the rear of the car a bit this may also help the bleeding process. Don't give up and if you are still having problems give a one of the mobile mechanics a call.


:beer: :beer: Steve

Hi Steve,

Yes it's been bled properly, TBH I can't afford to have a mechanic out it's already cost close to 1k in repairs.

mgtfbluestreak wrote: cant comment on the jiggle valve.....have you replaced the expansion tank cap....has these can be a common failure has the preasure in the system has to be maintained

Sorry I forgot to say I've replaced the cap with a genuine one.

and youve had a lovely new rad fitted?

It certainly does sound like air in the system or a blockage somewhere.
I'm sure someone with more knowledge than me will be along soon.


:beer: :beer: Steve

mgtfbluestreak wrote: and youve had a lovely new rad fitted?

Yes a brand new alli rad. Just off out again now to bleed it & see if there's any air.

I've just replaced the heater jiggle valve with a known good one & the car still overheats when the heater is on cold, should there be a constant stream from this valve or not? Tomorrow I'll be fitting stat number 4, a 82 degree version this time though.

Check that the heater hoses are connected about the right way, some cars get all sorts of trouble if the flow goes the wrong way.

Not sure which is the correct way if I'm honest, the left hand under car pipe is the flow into the bottom of the rad & the right hand side is the return from the top of the rad, the return connects onto the metal engine pipe which goes to the stat.

Can anyone tell me if this is the correct PRT I need & will anything else be needed for the conversion?

Thanks.

I wasn't referring to the radiator, I was referring to the heater matrix (cabin heater)
If they're connected the wrong way around, it could cause an air pocket that can't be bled off properly.
Looking at a diagram in the manual, the heater hoses cross over one another on their way to and from the engine, so it would be easy for someone to get them arse about.