27 replies to this topic

[john2502]

Hi all.

So the car (2000 MPI) was in for MOT the other day and guy left it running for a while in a hot garage while taking a call and the temp went up a bit (usually stays perfect) to about 3/4. Then drove it to work and it kept rising.

No worries i thought, been planning to do coolant change/flush for a while so will get on with that.

Anyway, have replaced the coolant and flushed the system, replaced overflow tank cap as saw this mentioned can be an issue, and still overheating.

It goes to the middle of the gauge for a while and stays there for a few mins, then slowly climbs right up to the red.

Any ideas? Only further thing i can think of is thermostat but is there anything else I'm missing?

I've made sure to "burp" the system so I dont think there's an airlock, I ran he car up to temp with cap off the overflow and gave the bottom hoze a gentle squeeze, with cabin controls on hot. Also wouldn't have suddenly been one before I did the flush surely, if that makes sense.

Any other ideas? Thanks very much.

[john2502]

Just a note car is daily driven so not been sat for a while or anything and as I say always been fine temp wise. Cheers.

[dan1zo]

Hey, i had similar with mine. Try taking a look at the thermostat. In mine it wasn't opening at temperature and so wasnt going to the radiator. They arent expensive. But test the existing one first.

[sonscar]

Does the fan run?Steve..

[john2502]

Yeah thinking only other thing is thermostat surely. Ordered one from minispares just now.

Oh yeah fan runs as normal, should have mentioned. Cheers

[Ethel]

If the gauge climbs then hangs around normal for a while that suggest the thermostat opened. Slowly climbing suggests a general lack of cooling. It could be the thermostat isn't opening fully but is could also be obstructed flow, water or air, through the radiator. The water pump is also a possibility, check the belt and though it's likely the last resort it's not unknown for the impeller to get loose.

[Steve220]

Remember the gauge isn't linear. It works on a PWM that levels out between 86-105 degrees C when central on the gauge. Red is c120 degrees. 

 

Few things i'd try:

 

1) drop the coolant and reverse flush the system - especially the radiator. The rust silt can build over the years and start to clog it.

2) replace the thermostat (88 degree one)

3) fill with fresh coolant with the heater open. If you fill it slowly, you'll get most the air out without having to burp it.

[john2502]

If the gauge climbs then hangs around normal for a while that suggest the thermostat opened. Slowly climbing suggests a general lack of cooling. It could be the thermostat isn't opening fully but is could also be obstructed flow, water or air, through the radiator. The water pump is also a possibility, check the belt and though it's likely the last resort it's not unknown for the impeller to get loose.

It does sound like that doesn't it but I drive the car every day (literally) and so it seems more like something has suddenly gone as up until now the gauge has always been fine.

 

I wonder if the thermostat opened then closed again possibly. Either way i think i'll replace that as my first step but yes will also check belt and water pump. thanks so much for the reply

[john2502]

Remember the gauge isn't linear. It works on a PWM that levels out between 86-105 degrees C when central on the gauge. Red is c120 degrees. 

 

Few things i'd try:

 

1) drop the coolant and reverse flush the system - especially the radiator. The rust silt can build over the years and start to clog it.

2) replace the thermostat (88 degree one)

3) fill with fresh coolant with the heater open. If you fill it slowly, you'll get most the air out without having to burp it.

Gotcha yeah, good point.

 

So the system has been pretty thoroughly flushed through this week, i drive the car every day so this feels a bit more like something has suddenly failed as before then temp has been perfect.

 

i think thermostat is my next port of call (especially as it arrived earlier today) but will go from them, will feedback if this works.

 

Many thanks

[john2502]

Just ran the car up on the drive, behaved totally perfectly needle went to middle and stayed there for ages despite being sat still in the hot sun. So have held off for now (as i need to take it in for it's MOT re-test tomorrow morning so want to get that out of the way first).

 

I did notice a bit of a weep between the thermostat housing and block, there seems to be an almost uppver gasket on the thermostat housing itself and then one between the housing and block if that makes sense?

 

I would be surprised if this has caused it to overheat as coolant level has hardly dropped but still isnt ideal. Hmmmm.

 

Will post some pictures before i have to shoot off and pick the kids up (not in the car)

[Steve220]

One thing else to give a go is to clear out the line between the thermostat housing and the expansion tank. When you take the hose off the stat housing, run a drill bit through the hole.

[john2502]

One thing else to give a go is to clear out the line between the thermostat housing and the expansion tank. When you take the hose off the stat housing, run a drill bit through the hole.

 

Ah ok cool will try this as well yeah, thanks

Edited by john2502, 17 July 2026 - 02:37 PM.

[john2502]

Pictue attached hopefully but I am doubtful this is causing the car to overheat surely.

Attached Files

•  20260717_163803.jpg   45.99K   0 downloads

Edited by john2502, 17 July 2026 - 03:45 PM.

[john2502]

Hi all. So thermostat and gasket replaced by decent local mechanic I know.

He noticed the electric fan had been staying on a bit so he thought it may be the temp sensor thinking the car is hotter than it is. Noted it came on even when the car was cold so asked if I'd wired it to do so (I haven't)

Well I drove home ready to order replacement sensor. Again car did as before got up to temp ok, stayed there for a while, then gauge stated to climb up to red.

Nursed it the short way home and the coolant was boiling in the tank visibly.

So I'd now definitely say its getting hot and not necessarily the gauge.

I am a bit stuck now as was ready to blame the temp sensor and possible that bit of the loom as have seen it was a recall and mini spares sell a replacement part of the loom for it specifically but now.....well I'm not sure.

So its had a flush, new coolant, all lines seem clear and radiator gets hot all over so can't imagine any blockages. New thermostat and gasket.

Only other think I can think is maybe water pump isn't pushing much around but when its running you can see coolant returning to the overflow so I'm not sure still.

Eugh.

[john2502]

Oh sorry and its had new overflow cap too.