Coolant Temp Rising & Falling
 

Out on a run the day with my local scooby club & half way through my Coolant temp shot up & heaters started blowing cold.

After checking coolant level decided to call it a day and turn back only for the temp to drop back to normal within second & blowers blowing hot again.

Over a 15 mile drive the temp gauge was up n down like a yo-yo.

I replaced the thermostat about 6 months ago so I have come to the conclusion that it make be an air lock

Anyone else suffered this problem before?

If it is an air lock what is the general procedure on bleeding the system on a STI v3 classic

cheers for any help

Scotty

Could have an airlock but I'm no expert.

if it was 6 months ago you changed the thermostat i think it is unlikely to be an air lock from that

could be head gasket on its way out pressurising the system

You said you checked the coolant level - did you have to fill it up at all? How often is this happening or was it just the once

Have you checked for coolant leaks?
I have had in the past a mystery coolant loss & eventually found a tiny hairline crack in a hose that would only open up & let coolant out on high revs under load (i.e: under extreme pressure). You did mention you were on a club run & I imagine you weren't going slow!

Headgasket possibility?
Easy to do a block test - can be bought from most motor factors or a garage will do it for you for £5-10. In a nutshell, a blue fluid in a tube with vent is placed on top of expansion tank when the engine is warmed up. If any gases have seeped through the headgasket into the cooling system then the fluid will turn yellow.

Water pump?
Could be on it's way out - will show up even more when under high pressure. Any bearing noises coming it?

There are loads of reasons why this could be happening such as one hose clip may not be tightened up enough so when put under high pressure it may suck air in. Check all hoses, especially ones round the thermostat if they were the last ones disturbed.