2003 year of reg'n, outback, 100k miles done.  Motoring along, air con starts blowing hot not cold air then engine temp up into the red for 10 mins, followed by return to normal.  On getting home checked radiator level and added about a litre.  Some signs of wet, probably coolant on the engine protection plastic floor.  Driven today about 50 miles all seems fine.  I'm concerned though that something's up.  No strange mechancial noises at all, electric fans fine.  Some water gurgling noise on starting engine this morning. Any ideas anyone?

That sounds like early signs of head gasket failure. The gaskets tend to break up between the combustion chamber and the water jacket that surrounds it. Compressed gases get into the coolant system which increases the coolants volume. The excess is forced out of a tiny overflow hole in the overflow tank. That's where you get the wetness from and the lower level of coolant.

It's rare on Subarus to get the classic sign of head gasket failure (oil and coolant = mayo).

The one way to check for certain is to go to a garage and ask for a sniff test to be done. They should have a device that suspends a chemical above the radiator cap. The fumes will send the chemical a different colour if combusted material is in the coolant.

Ouch. Thanks very much.  Now even more concerned!  Drove it hard for 50 miles last night and no further prob but that wasnt an imagined event and so something's up.  Sniff test here we come.

Do the sniff test with exhaust gas analyser probe, far cheaper & just as accurate.

Do check for obvious simple leaks first ...

Actually, that's a good point. In your first post you mentioned an area of wetness on the under tray. That obviously has to have come out of a pipe or a component.

Take the car for a drive and get it up to temperature. With the engine running, lift the bonnet and have a look for where the coolant is escaping. My original though was the overflow tank, but it could also be that the radiator has sprung a leak. You may need a torch at this point. With the engine running and up to temp, look down the radiator end pieces. You should be able to see engine side quite easily but you will need the torch to see down between the rad and the slam panel.

If the coolant is on the undertray on the passenger side and the rad looks fine, it could be the water pump but you won't see that as it's inside the cam belt covers.

As said above. If it's a leak on the rad I'd almost put money on it being the bottom hose or the bottom corners. Fingers crossed it's just the leak and not a Head Gasket :( 

have you checked for any air locks in the coolant.

Short drive, up to temp, no leaks visible at all no noises.  The damp on the floor panel is on the passenger side but hasn't got any worse, no sign of any leaks.

Bottom and top rad hoses all look and feel fine.

Havnt checked for air locks in the water, although have run the engine with the rad cap off and the level is steady, liquid looks clear/good.

I wonder if the water pump could have failed for a short period then somehow started again.  That might explain the brief period of very high temp followed by no symptoms.  Seems a bit odd though to briefly fail....

The advice to use a torch was good.  Ahem, I don't think this is connected to problem 1 but the torch reveals grease on the steering shaft, a fair bit of it and it's on the rubber boot on the drive axle behind it.  Grease... where the heck has that come from?  The steering rack perhaps?  Looks a bit of a mess but no obvious impact on performance.

Sorry to add another challenge.  By the way the mileage is 80k not 100k, I've owned it since new.

Thanks for all the good thoughts.

Richard

Probably a split cv boot on drive shaft throwing grease out.

Kind of impossible for pump not to pump for short time but a pump leak could be involved & be intermittent.

You certainly want to keep an eye on it & that grease issue needs looking at/fixing (not big job that)

Ideally the car wants looking at on the ramp with plastic tray removed & take it from there, this could be done when boot/grease issue resolved.

Thanks.  I think I'll get it to the professionals in this case.  Thanks for all the excellent support.  Richard