Hi sitting waiting on some one for five mins noticed my temp gauge was at its highest mark turned engine off popet the bonnet water was boiling left it for 20 mins checked my back up water bottle it was empty toped it up with 1.5 litters of water drove home no problems no over heating and air con still running hot checked next day water fine not dropped started looking for bubbles had none all seems fine drive it 150 miles and no problems since what do u think??? Air pocket? Etc also since its running fine and not over heating do I need to worry my car is a subaru impreza turbo 2000 4wd uk model

 

I would get a sniff test done just to be sure it hasn't goosed the head gaskets.

And if you filled up with plain water, I'd be changing the coolant for the correct concentration of anti-freeze, 40-50%.

Failure so to do will lead to corrosion in the engine and possible freezing up this winter

 

Check the plastic end tanks on the rad (looking down with a torch) it's very common for them to split and cause grief when coolant is lost. If you're lucky it just got hot because water had escaped (maybe via crack in rad) if you're unlucky the resulting water loss and air pockets can damage the head gasket(s)

 

Am I right in suggesting to identify air pockets in the system is to stick a funnel in the filler cap securely to avoid spillage then to let the car warm up until the fan kicks in and watch the level drop back down in the funnel and then top up accordingly?

Tried this on my last UK classic to help prevent an idle overheating issue.

 

No.

That's a myth, sadly.

You can only guess at having airlocks due to the car's behaviour.

You MIGHT be able to get them out by running it with the filler cap off, squeezing pipes etc, allowing bubbles to escape and topping up as you go on, until the fans kick in.

But the onlyy sure way to avoid an airlock, or get rid of one, is to drain and refill PROPERLY: do a search under my name, I've typed a how to many times.

 

Well iv drive 200 miles since with no problems no over heating or loss of coolant thinking it was just air plus the fact I never checked the water since last year still blows hot and no bubbles neather so think iv been lucky this time ill get a full flush before the winter just to be sure

 

I'd still check the rad. Air doesn't just appear and it's all fine and dandy

 

Check that your cooling fans are working.

If you were sitting waiting with the engine running, you are relying on the fans to come on to prevent over heating as there is no air flow through your radiation when stationary.
If the fans don't come on, it will boil and lose coolant.

Have you replicated the situation from when it happened originally? Or have you just been driving it? If you are driving it, there will be air flow through the radiator, so it won't matter if the fans work or not.

 

Mine tried to cook itself a few years back.

It was a combination of a goosed thermostat, and the fan not working.

As above, make sure you run it upto temperature, whilst stationary to make sure the fans working.