A brief overheating

[Tony Francis]

Ten days ago my Zed had a new coolant flange fitted as the original was cracked. All seemed well, a couple of hundred miles later and temperature gauge spot on and car running perfectly. 1.9 M43 engine.
Today the wife and I went to a local charity garden open event, bit of a queue to get parked and just as I am about to park up I notice the temperature gauge is at 3/4 mark, then steam appears from under the bonnet!
OK, don’t panic! Get into the parking spot, about to switch off but the gauge has moved back to the normal 12 o’clock position and no more steam. I let it idle for maybe 30 seconds, temperature stable so switch off and go to look round the gardens while car cools down.
Time to go home so up with the bonnet to check coolant level and look for any obvious leaks. Level down a little but still visible in the header tank, no signs of a leak, no puddle underneath the car. Hmmmm, I decide to try to get home (about 15 miles), car runs fine, temp gauge spot on again.
So, what could have caused this brief but worrying moment? Is it possible that there was an air bubble in the system that worked its way through the system and vented through the pressure cap pushing a little coolant out? Would the pressure cap even function like that?
I am going to check everything again tomorrow when engine is cold, but I am puzzled.

 

[Duncodin]

Maybe a sticky thermostat. Or fan didn't cut in when it should.

 

[Pond]

As the coolant system has been 'altered', you probably have slight air somewhere in the system.

I would fill the expansion tank (if needed), get it up to temperature at a standstill, with the heater on full, and see what it does.

You may be lucky that the air released via the cap when it temporarily overheated, but it needs checking.

 

[Tony Francis]

As the coolant system has been 'altered', you probably have slight air somewhere in the system.

I would fill the expansion tank (if needed), get it up to temperature at a standstill, with the heater on full, and see what it does.

You may be lucky that the air released via the cap when it temporarily overheated, but it needs checking.

Yup, I am hoping that as well. I will be following the suggestion later so we will see what
happens.

 

[Tony Francis]

Right, looks like a small leak at bottom of the header tank. Is that straightforward to change on the M43 engine or is it a garage job? Anyone done this before?
Edit - quick search on here suggest it’s a new radiator job with header tank combined. Hey, ho, off to the garage then :-(

 

[AntStark]

When I had the water pump done I remember the garage saying it was a pig to get the air locks out of the system..they had it on ramps and everything. That rad is not that old if I remember correctly.

 

[Tony Francis]

When I had the water pump done I remember the garage saying it was a pig to get the air locks out of the system..they had it on ramps and everything. That rad is not that old if I remember correctly.

I will have a look back in the service records Ant. The header tank plastic is very yellowed, I wonder if it was reused with the new rad.