Morning all,

07 plate STi with 50k miles.

Ok, so I want to check both my caps out whilst cold yesterday.


Both show no signs of wear, perished or leaking etc, so all good (I think)


Firstly, the header tank cap (nearest the turbo) has a small disc which I can easily pull down 3 or 4ml perhaps, so I'm guessing it's not seized? I also gave it a good clean.


However, assuming this return valve is working fine, why does the water in my overflow non pressurised tank by the radiator, not go back into the header tank? Or, not as much that goes into the overflow tank anyway.

After giving the car some beans / boost, the overflow tank can get pretty full, but not a lot seems to go back to the header tank once completely cooled down. I have to manually take the overflow tank off an top up the header tank.

Secondly, the rad cap again shows no signs of leaks / wear, and I could push the spring in fine, but is the disc on this cap supposed to be able to pulled down like the header tank cap. I just about got hold of the disc, but I only used very gentle pressure to see if I could pull it down and I couldn't. I've not bent anything, just handled it with care.


I thought the rad cap had a return valve, maybe not? Rad was full to the brim with coolant.


Thanking in advance.

 

I'd hate to suggest this but sounds very much like headgasket failure symptoms. Get a hydrocarbon sniffer test done on the cooling system

 

I had one last year (same symptoms) and came back all clear.

 

Given that you have a 2.5 in an early hawkeye, the likelihood is that your car is in very early head gasket failure.

Boot it hard then get the test done.

 

But really though? I mean, I've been having these symptoms for well over 2 years!

How long can you get "early signs" for?

 

As long as you don't flex it too hard, I'd imagine.

 

What symptoms are you having exactly?
Is the car overheating/temp gauge fluctuating?

 

Nope, my PSI3 flight data recorder shows normal coolant temps and always has done. The needle never fluctuates. The car does get a fair life here and there, this is why in a way I'm surprised that the temp needle hasn't gone skyward.

No rough idle, no white smoke, no nothing.

 

Have you had the thermostat checked?

I have had an overheating problem recently which I though was HG failure, turns out it was the thermostat and a perished seal on the header tank cap.

To say I'm relieved is an understatement.

 

I can imagine! Not had the thermostat checked, but I'm not overheating.

 

If you are manually having to empty your ( overflow ) tank every time you have subjected the car to boost I'd say you either have a severe airlock or The heads are lifting ...
Is there any ( murkiness ) if you can call it that in the coolant ? Small grey fragmentation ?

Take the pipe from the radiator to overflow & instead of putting it in the bottle make it longer & run it up to your window . Secure it under your wiper blade .. Now take the car for a spirited drive holding boost . If your temps start climbing heavily & you have constant coolant all over your windscreen you have 1 or the other .
Make sure you take a bottle of extra coolant out with you , don't want to run dry now do we ..

 

Just change the pressurised header tank cap you might be pleasantly surprised.

 

Just a thought here, my header tank cap is a Subaru one, but it's rated to 108kpa according to the sticker which is approx. 1.1 bar.


Shouldn't my STi PPP have a 1.3 bar header tank cap? Is this why so much coolant is flowing into the overflow tank?


Here is mine :

http://importcarparts.co.uk/parts-info.asp?id=5747

 

Would make very little difference change it there not expensive or have you changed it.

 

No not changed it yet. Will keep the post updated.

 

Just made an interesting observation, after taking it out for some beans, coolant in the overflow tank was high, so I thought I'd feel the radiator top and bottom hoses. The top hose was pretty damn hot, but the bottom hose nearest the thermostat was only warm in comparison. Massive difference between the two in temp. I don't think this is normal, surely both hoses would be the same temp if the coolant was circulating as it should be?

 

Change the header tank cap check the thermostat (or change) make sure radiator isn't partially blocked then consider water pump. Seen engines changed and rebuilt over a faulty radiator cap and when rebuilt do exactly the same.

 

I have just fitted this one, as the seal was also perishing on my radiator cap.

http://www.scoobyparts.com/performan...d-radiator-cap

Certainly worth a try for £23.

 

I'd like to try one of those large yellow Lisle funnels on my header tank to purge out any air lock, can only see them on ebay in the USA.

Yes I have a big enough funnel in the garage, but it's making the seal around the opening of the header tank that bothers me.

 

http://www.importcarparts.co.uk/part...chKey=radiator

 

I have a brand new genuine STI one here that came from import car parts. I didnt fit it as i made a bespoke header tank. £30 posted
Remember import car parts charge delivery too so they are in fact £44 from them

 

I've got a Blitz 1.3 Bar (Actually 1.27) cap on the header tank and an OEM 1.37 Bar cap on the rad. Seems to work well. Replaced the them as the header tank cap seal was going and hissing.