Scooby125

Hiya, after a hard run in my 95 sti ra v2 tonight, I checked the coolant expansion tank and every so often, the coolant would heave up and down like as if the level would raise momentarily and go back down again and do it intermittently. its not as if the collant was boiling hot as I could actually stick my finger down the expansion bottle and touch it with my finger. Ut was just warm.
I ahve heard of the coolant bubbling and resulting in a head gasket problem. Sometimes after the coolant rising in level for a split second, a kind of gas bubble would emerge but definitely not a boiling bubble.

What could this be. Is there an air trap somewhere in the system or is this another sign of head gasket problems.

Cheers for any help

911

If a gasket has gone, the bubbles continue (after a long HARD run) even when the engine has just been switched off.
The bubbles are not as 'big' as you would associate with boiling water in a kettle, but a gentle run of 'baby' bubbles.
In very extreme cases (like mine was) the car will jetison all the coolant down the sde of the car out of the level tube by the battery in 30 seconds!

Could well be trapped air, but if you havn't drained/refilled the system for several weeks then I suspect the gaskets will be suspect.
Try running the car to the max with the heater full on incase there is air trapped in the under dash matrix.

Good luck, hard and $$$ job to do the heads.

Graham.

john banks

Mine bubbles away in the turbo for a few minutes after switch off and sends the bubbles out through the cap into the expansion tank.

Scooby125

Thanks lads, well the system was drained and refilled a few weeks back but was done by a mechanic. The bubble I am referring to is just one fairly big one when the level rises momentarily and then goes back down.
Would the temperature of the coolant now be very high if the head gasket was gone? The coolant can be touched so only warm.
Cheers.

911

Coolant usually gets to about 85 deg C so would BOIL you!
Don't understand why the coolant is so cool.
Easy to have an air lock in the Impreza system, especially if you rush it when filling. I take 30 mins doing mine.

John's turbo boils it's water because he has TOO much bhp!

Graham

Scooby125

Thanks Graham,

You could be after hitting the nail on the head there, I was a bit surprised that I could actually touch it as I out my hand on the side of the expansion tank first off to check and that was cool.
Would this be pointing more towards a blockage somewhere or at the very least some trap on the cooling system.

Would you recommend I drain and refill or is there a shorter way of solving it? If there was an air block or something, what could this potentially have been doing to the engine???

Cheers.

911

I would drain the lot. Catch the contents as it is nasty to the environment!
To fill:

Drain every drop from the drain in the rad (plastic so take care). Open the heater valve with the engine on (not running)as i think the valve is electric. turn engine off.
With rad closed off, heater 'on hottest setting' slowly fill back into the header tank about 1/2 litre at a time or untill the header is brim full.
Gently squeeze the top hose (the big one to the rad from the block) and release; this will 'swallow' the water. Repeat until no more water is swallowed.
Keep doing this time and again untill about 5 litres (maybe less) are in the system. (this is why it takes a long time)and the header tank is full. Leave cap off.
Start the engine and tick-over to warm it up.
Quite quickly the stat will open and the system will drain the header. You will see all swirling of the coolant (a good sign the pump is working!), keep topping up the coolant into the open header tank.
Keep going until she will take no more!
The water should now be bloody hot, even steaming on a cool day.
Replace the header cap and run the car for a few more mins.Check temp gauge all the time.
The heater should be nearly melting the interior now, the temp gauge showing 'normal: 1/2 way mark).
Relax.
Allow to cool down a bit (2 hours) and check header level. Fill if low.
Re run the engine to full heat and rev the car for 30 secs to get the water really going, about 2500 rpm will do.
Check the level tube by the battery. It might be indicating something or not. top-up untill FULL mark reached.

Job done.

You can turn the flippin heater off now...

That's how I've done mine for 3 fills now and it has always worked for me.

Good luck. come back if you wish if all is not well.

Graham

Scooby125

Cheers Graham,

That sounds like an excellent account of how its done. I will go at it at the weekend and let you know how I get on.

Markyboy uk

I'm thinking of doing a coolant drain/replace too.

Graham, It's safe enough to leave the radiator filler cap off with the engine running? - It's not going to bubble or spit coolant out or anything when it gets hot?

By "Open the heater valve with the engine on (not running)" do you mean turn the fan speed on to full speed or am I missing something?


Thanks
Mark.