Ok, so when I bought my WRX in November I noticed there wasn't heat blowing into the car. One mechanic was convinced it was the head gasket.

Symptoms: lack of heat obviously - nothing else! engine temp always around half even after hard driving, no milky oil or smoke.

He said the water was pressurising out of the tank when revving with the cap off.

I got a second opinion and checked for airlocks + replaced the heater matrix. Now I went from absolutely no heat in the car to lots of heat when starting a journey but dropping in and out depending on how cold it was outside and how high my RPM was.

A guy viewed the car yesterday and after taking it around the block took off the lower radiator cap/overflow and while the engine was running revved the car, water gushed out of the tank. Now I'm not a mechanic but my friend who is said that is bound to happen because the car is running and the system is pressurised.

My next step for the intermittent heat issue is replace thermo and then water pump. Am I wasting my time? how to tell the head is really gone without replacing it!?

Many thanks for reading

 

Sniff test at a garage

 

You can buy a sniff test kit and do it yourself for £20 or less. Original no heat sounds like an air lock. Was the coolant system bled up correctly before changing parts?

Worth doing a sniff test anyway just for peace of mind.

 

You can't properly bleed the coolant system on an Impreza.
Best method is to drain it down and do it again, after reading up how to fill without airlocking.

 

Thanks guys, incidentally now the outside temp is milder 3 - 5c the heater is much better - seems more intermittent at -1 - 2c

My mechanic mate said he pressure tested it and used some dye that turns yellow if something is wrong - the car was fine (stayed blue or whatever colour they use!)

 

I'm not up on these engines but on most engines when you rev or indeed drive the car the water is pushed around the engine to keep things cool no? So taking a cap off its obviously going to gush out, the fact it's bubbling could suggest there is a air lock. And your heat could be a sticky thermostat, had the exact same problem on mk2 golf years back, in the milder weather it worked the heater fine, in the cold it wouldn't blow warm air

 

I'm getting all these conflicting opinions, what symptoms should I be seeing if my head gasket has gone, even if it's an early stage failure?

 

airlock, and it will come out the tank when revved.
wait till its cold and take off the header tank top.
turn the heaters to full hot and full speed on blower fan.
start the car and let it run for 20 mins or so, you will see bubbles coming through the water int the header tanks, this is the airl ock disappearing.
when its run for 20 mins top the header tank up and put lid back on.

 

The system i use is, take the pipe that goes to the plastic overflow bottle, extend it up under the bonnet & clip it to the windscreen wiper, making sure you don't crush it with the bonnet closed, drive the car to normal temps, when it comes on boost hard if a gasket has gone you will get consistent amounts of coolent loss from the pipe, the first couple of times might be getting levels sorted if you have topped up the system, but after that it should settle down, if not & your still losing consistent amounts, its a gasket issue.
Wash the excess off when finished.

 

Thanks for the advice guys wish there was someone with Scoob experience near by I could pay to diagnose it!

 

That's the sniff test, so the HG is fine!

You place a sensor over the radiator filler and it detects the presence of any hydrocarbons. If it finds them then combustion gases are leaking in to your cooling system.

You can get kits which do the same thing and use different chemicals to give you a result using different colours.

Blue = Good, Green = Bad, Yellow = Fooked HG

 

Yay!!!!!!!!!!!!

 

airlock, do as i suggested first, its free and easy

 

Looking at that list, never overheats, I do have the heater issue, new matrix brought heat back (intermittently), A guy viewing the car after driving around for a while took off the lower /over flow cap and pulled the rev cable which had water coming out of the tank - said this was head gasket fecked - sniff test was fine

 

Hi tommy, will definitely be following what you said this weekend!

 

I had a very similar problem and thought the same but my sniff test was also ok. For mine it was a fooked heater matrix. Yours as Tubby says does sound like an airlock though.

 

Forgive my ignorance, the header tank is this one right:

 

Yep.

 

yup

 

Aye.

 

Maybe thermostat

 

Have a new one ready to go in, my next step!

 

Ok so tried the air lock advice - the blowers were still cold after 25mins, worth a try