Broken thermostat?

[Gilb666]

Hi All

I replaced my coolant last week after a hose burst, took the car for a drive and all seemed fine, but i forgot to screw the cooland cap down and came back to the car yesterday to find the tank empty. Topped it back up, it took about 3l so there was still something in there, but after another drive around it seems to be getting hotter than i'd like sat in traffic and returns to about half way when i'm on the move.

I replaced the rad last year, and the cooling fan is working. I also put in a G60 thermostat at the same time and on a run last weekend before the pipe burst it was sitting happilly at just below half in stop-start traffic on the motorway for an hour.

Not sure if it's related, but the heater fan motor just cut out about an hour before the pipe burst. wasn't making any odd noises before this, and turning the knob still causes the voltage to drop a little as usual

[unknownmale]

When it's up to temp feel the coolant hoses to see if they're all warm, put the heater to full hot (You don't need the fan on)

[Gilb666]

Before i left the cap loose i did test this, bottom one stayed cold for a while then did heat up. I'll check it again tonight cheers

[mark1gls]

When you top up that much coolant you may need to bleed the air out of the system, set the heater to hot and when the car is cold remove the filler cap on the expansion tank and start the car, you should see a a trickle of water from the thin hose going into the tank and as you rev the car more water flow should increase, if the level drops add a little more coolant, run the car for about 5 mins with the cap off and check the level then put the cap back on and let it warm up and you should feel the hoses get harder as pressure increases.
Let the car cool down and check the coolant level again, preferably leave it over night.

[Gilb666]

Didn't get chance to do much investigation last night as i needed to go out, but i did check the coolant level before i set off, which was fine. The temp stayed between 2/3 and 1/5 all the time i was driving, which is normal with the G60 thermostat. I'm thinking there could have been an air lock that worked its self through the first time i was driving?
I'll try and get out early and give it a propper once over this weekend before it gets to hot (Not something you expect to say often in England!)

[Gilb666]

I've done as advised, i can see the pump is working, left it running for 5 with the cap off but the temp did make it up to just beyond half over the next ~15 mins.
Hard to tell if the pipe pressure went up after the cap was replaced - didn't seem that much firmer to me after running for 20 mins, but the pressure cap was difficult to remove an hour later, so there was certainly some pressure there.
The bottom pipe was cooler than the top to start off with but the temp did come up after a while which i think means the thermostat should be working?

[mark1gls]

Buy a new blue cap for the expansion tank and see if that helps, avoid the black caps.

https://www.ebay.co.uk/itm/VW-GOLF-MK1- ... Swvg9Xe5Me

[DannyH]

Buy a new blue cap for the expansion tank and see if that helps, avoid the black caps.

Sound advice

[Gilb666]

Bought a blue one last year - it seems to 'seal' a lot better when the engine is warm.
The car seems to be behaving its self now the weather has cooled a bit. I have been driving around with the heaters on, so hopefully if there was an air lock it's found it's way to the expansion tank now.