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Hey Crew

My noble stead overheated on me yesterday. It's a 1998 outback which I understand is pretty common on these things. Luckily I saw the temp gauge start to rise and shut her off. Ended up crawling to an incline, unscrewing the bleed screw, filled with coolant. Turned the heater on full and was getting cold air from the vents, no coolant flow? Eventually after more coolant/bleeding I started to get some warm air coming out so chanced the drive home and it sat bang in the middle the entire way home.

Had the head gasket tested with one of those pressure gizmos that has the solution which is supposed to change colour if there is a leak, all seemed fine.

I'm thinking it was likely an air lock, but what would cause it?

Cheers,
Nick

Before you can just say 'air lock' you need to ask why is there air in there?

Have you just changed coolant/radiator etc and not bleed the air out properly?
Or do you have a leak and it was low on coolant?
Or do you have a problem that caused overheating and that pushed all the coolant out?

I wouldn't put too much faith in the head gasket test:
A: They're notoriously unreliable
B: All aluminium engines/steel head gaskets can be very hard to prove.

So, you need to work out where the coolants gone: Fix that then you can look at the circulation of the coolant, then look at if it's a head issue. The days of simply saying "thermostat/water pump/blocked radiator' etc are well behind us now.

I've had customers with dodgy head gaskets that have taken months to prove. They keep loosing water, can never prove where it's going, pressure testing hot/cold etc. shows nothing.

Suby Spanner wrote:The days of simply saying "thermostat/water pump/blocked radiator' etc are well behind us now.

Not quite, my 2003 XS Forester had a blocked radiator and I used rainwater to fill it and the windscreen washer bottle.
03/17/2011 and 178,405 kms later the Temp needle shot up into the Red Zone, I had to replace the radiator because the cores could not be cleared by a radiator specialist shop.

Workshop (Subaru specialist not Dealership) said it was sand, akin to the type used when casting the engine. The radiator was approx. 1/4 full of it.

Cheers for the reply's.

I'm just travelling and bought the car a month ago, haven't done a single thing to it apart form making sure all fluids are in check. They've never moved apart from this saga.

No visible leaks in coolant, the level has remained constantly full since.

Interesting point on the radiator, might be worth getting it flushed.

Stuck for ideas as I planned on taking this thing for a road trip in the next few months but don't want to end up stranded.

As Subyroo rightly says, the cores block up. This isn't just a suby issue. How old is the rad? Flushing it doesn't really do or show what's needed. You need one of the tanks taken off to see flow through the tubes. Given the price of new radiators, it's more economic to replace than repair though.

Don't skimp on a radiator if you replace it though: See your local rad shop for a replacement. There's a lot of junk on the market when it comes to radiators, and failure has a hefty price.

If your 1998 Outback has never had new head gaskets or a radiator then it would be a good idea to get them replaced. head gasket interval was around the 150000km from memory.

TOONGA