CC

Been to view an early wrx, everything seems ok except for one thing that puzzled me - loads of pressure in the coolant system ie on removing the header tank cap after the car has been running for a short time, the coolant seems to be under loads of pressure and spurts out of the header tank.

There are no other symptoms ie no oil in water or smoke from exhaust. But i know from experience with other cars that this is a classic symptom of h/gasket failure or at best a blockage?

Is the impreza different in that such a pressure build up is normal for this car? My 'mechanic' friend suggested this might be the case?

Any opinions much appreciated

Chris

Hndatch627

there's at least 16psi of pressure in your cooling system, remember that fluids expand and contract with temperature, when hot the fluid has expanded and is exerting the max amount of pressure it can against the cap. Now if you take that cap off a .5" or 1.5cm hole in the radiator becomes like a common garden hose just free flowing. It sounds normal to me

jeremy

dhorwich

I had similar thoughts... then i went out to my dads brand new IS200 lexus which had only done 1000miles and his was exactly the same..!!! its just that they have a pressurised cooling system, if it was a head gasket problem the coolant overflows all the time into the overflow bottle which is just in front of the battery..!

Dan

[Edited by dhorwich - 12/18/2002 10:08:16 PM]

CC

thanks guys

tweenierob

If there is at least 16psi pressure in the cooling system then why are scoobs fitted with 13psi caps??
The higher the sustained pressure in the cooling system the higher the boiling point.... This would mean that our cars would need at least a 17psi cap to keep the pressure??
Rob..
I am confused

Hndatch627

Rob if you look at your radiator cap it has a number on it that says 1.1 that reading is the pop-off point...note it's also in bar. 1.1=15.95psi

STi cap is 1.3 bar=18.85psi

don't use the STi cap with a standard WRX radiator or you'll end up with a cracked top tank or blown top tank seal.

jeremy

AndrewC

So is the STi header tank stronger than the std WRX one?

I've seen many a scoob with weeping header tanks/caps at track days.

Andrew...

tweenierob

I think you need to explain a little more clearly... How does a water system sustain 17psi pressure when the cap opens at 16psi??
STD cap is 0.9bar.... afaik
STI cap is 1.3bar?? i know the STI's have a higher pressure cap.
Not to sure what the difference is between an STI and non-STI header tank
Not sure why there would be more pressure in an STI water system?? after all, the 98 WRX is 280ps and so is the version5 STI if it was due to power maybe a difference between early 240ps models and STI models...
Maybe i need an STI header tank for my WRX??
I am a bit concerned that i have the wrong Cap on mine now....
Rob

MorayMackenzie

The warning on the coolant header tank cap that says "never open when hot" or similar is there because the system is pressurised.

Maybe Gridlock Mikey could advise as to wether or not that particular warning should be heeded or simply disregarded.

dhorwich

tweenierob,

I think the early cars where 0.9bar..!! my MY95 WRX is 0.9.. but i think some of the later ones where 1.1bar... then 1.3 bar for the STI..

Dan

tweenierob

Nice one Dan
Was a bit concerned that my cap is only .9bar
Rob
p.s. hows the progress on your car mate?? hopefully not a sore point??

[Edited by tweenierob - 12/19/2002 6:28:38 PM]

silver:scooby

the reason all cars run pressure in the cooling system is to raises the bioling point of the water. Water boils at 100*c at normal atmospheric pressure, which is no good cuz most modern cars run at 90*c which is to close to its bioling piont. So if you raise the pressure you raise the boiling point so say at 0.9 bar water will start to boil at 120*c and still give of heat to the ambient air

thats the basics i know its a bit more involved than that but you get the idear.

dhorwich

tweenierob,

Its getting there, its in the body shop as we speak still waiting for the headlight panel e.t.c, but the mechanical work is done...

Just found out that i have to wait another 3 weeks for a new 19" wheel, so not to happy, plus if i want to put my old 15" crappy wheels back on then i have to take my 4 pots off the front and i cant be doing with that..!!

Dan

bandyandstrange

just to put every 1 straight lol


best way to check if it is the head gasket you must have a cold car undoo radiator cap to let any residue pressure that maybee in the system replace cap start hold at around 3000 rpm for 30 -45 seconds turn off undoo the cap again if there is a lot of pressure in the system ie lots of noise and coolant spurting out then you have compression gas leaking into the cooling system serious problems somewhere .

just my experience after 12 years in the motor trade
hope this helps
mark

wrxrob

or u could just do a carbom monixide sniffer test on it or a good old fasion coolant pressure tester will tell you.

oh and it would be pressurise when you take the cap off because when you pressurise water its boiling point is raised?