please help, advice needed

[chris182cup]

after driving for an hour my car stop warning light came on and the car was over heating ( very hot )

i opened bonnet and it looked like the coolant was either boiling or there was air bubbles going through it, also steam from near radiator somewhere.

as soon as i turned the heating up full the temp when down no problems

my brother told to open the radiator cap which i could not see anywhere, what i did see on the top left was a hole the size of my pinky which looks as though its threaded to take some sort of bolt/screw but this could be nothing

could this have been caused due to not enough antifreeze/coolant and too much water ? it could just have frozen up as it was -13, but i drove up the road when it was -17 or so and it seemed fine.

could someone please give me some advice if u think it was a one off due to the cold and the coolent freezing or advice on what else to check, it did drive ok for 3 hours after this incident but the heating was on hottest it would go but not on full blower

 

[Da]

Sticking thermostat at a guess.

When he said open the cap on the radiator, he meant the expansion tank/coolant bottle on the bulkhead, but I wouldn't open it whils it was boiling!

 

[chris182cup]

no i know that i dont want scalded lol, he thought it would have a cap on actual radiator but its a closed loop system he thought it might have trapped air in there somewhere

will run it tomorrow with the heating off to see if it overheats and join the AA just incase

going to check for yellow goo on oil cap, hope its not head gaskit

 

[Mark One]

Dude! -17 in glasgow? WOW

anyways, it's something coolant related. If it's overheating, then it's normally one of 2 things, thermostat stuck shut, or water pump failure.

The Thermostats (thankfully) normally fail OPEN, causing overcooling. But the cold weather may have caused an issue.
The Water pump may have failed due to icing over. This can be common on VWs with plastic water pump impellors - the plastic impellor works itself loose of the drive spindle and you get no pumping. I don't know what an F4R water pump looks like so I don't really know if this is likely.

If i were you, I'd give it a bit of a rev with the bonnet up - see if you can see any coolant being pushed back into the header tank (filler bottle-top right). That will tell you if the water pump is working. There should be a good bit of flow that increases with engine speed.

If that's fine, change the coolant for a good strong mix and definitely a new thermostat at the same time, they are dead cheap anyway.

 

[chris182cup]

it was in the highlands it got to -17 not in glasgow

im starting to think the coolant had froze the coolant wouldnt boil but it was bubbling i didnt look at it properly to see if it was frozen

it worked fine once the temp picked up a bit, so hopefully just the cold causing problems