Hi All

Yet another question from myself!
I am trying to determine whether or not I have early head gasket failure or if I am just being paranoid.
Car is a sti v3 1997

Symptoms:
Header tank level drops about an inch after a few spirited runs
Weirdly the expansion tank level does not drop at all
Temp gauge does not go into red line at all
Car has full power at all times
No smoke out exhaust
Odd bubble in expansion tank but not consistent at all
no bubbles in header tank (where coolant level is actually dropping)
Sniffer test done and came back negative
Slight engine vibration at idle when cold (although I do think it is mount related - revs remain constant and engine note remains the same)

What I have replaced to date:
Coolant tank cap
Coolant
Radiator (found a hole side of radiator)
radiator hoses
New water pump (apparently done at my request when I bought car)
thermostat

I have been filling the header tank right up to the neck. The bit that puzzles me is why the header tank level drops but the expansion tank level remains ok - strange
How full should the header tank?

 

Quite often the metal pipe which runs across the top of the rad to the expansion tank gets blocked internally which is why
the level never changes.

 

Thanks - in that case where would coolant escape if I did have a hg issue?

It strongly think it is not blocked though as I have topped it up via this pipe in the past. Also when changing rad coolant flowed from both the pipe to the expansion tank and the rubber hose attached to the coolant tank

could the coolant level be levelling out (albeit about half way down the header tank). Maybe I need to leave it at the dropped level then monitor to see if it drops further rather than topping it up

 

Have you changed the thermostat yet? Worth a go also. These can very easily get air locks in the system so would also be worth you checking all the pipes are free then burping the system to get rid of the air. Once you've done that if it drops again either you've got a leak or head gasket failure.

The sniff tests don't always reveal head gasket failure. Garage did one on my FSTI that showed early signs and buyer (Subaru mechanic for 15 years) did 3 more all that came back negative. Turns out it had still blown a HG though.

 

Yeah mate already replaced the thermostat.
I will check all pipes and maybe buy some of the dye to put through the coolant?

How full should the header tank sit?

Thanks so much!

 

The high pressure expansion bottle should always be full right up to just below the cap and the level shouldn't move at all under any conditions. The overflow bottle at the front will go up and down as the coolant heats up and things expand.

 

I broke my plastic header tank on my blob so bought a 2nd hand metal one.
I never noticed but when I took car for work to be done and a map the mechanic noticed a hairline crack in the metal one.
it would leak onto the top of the metal header tank but evaporate as it was so hot ,there was a bit of residue but I thought it was spillage from filling up.
worth a look.

 

Think it was a slight separation where the top was joined/crimped to the bottom part.

 

Thanks mate!

 

 

 

cap well well well
Had the turbo coolant hose have a leak on me after I was fiddling about with all coolant hose clamps making sure they were tight.
I decided to buy all new hoses and fit them, which meant draining coolant and refilling to do it properly.
When I had the car burped and switched off I noticed both my upper and lower radiator hoses were flat in a vacuum.
I took the header tank cap off and they expanded again.
Upon further investigation the metal valve on the header tank cap has failed and is not opening!
This was a new genuine uprated tank cap from ICP.
Swapped the old one on for now and will monitor. Interesting.
I wonder if this caused my hoses to go fairly hard and upped the pressure in coolant to the point where any weak clamp joins were compromised.
Now I think about it I was complaining about the overfill tank level not moving at all when cold or warm

 

This is what failed on my 1997 gc8 sti

https://importcarparts.co.uk/parts-i...y=&searchPart=

 

The round cap in the link doesn't normally have the vacuum valve fitted to it as the cap fits to the radiator on the Newage cars

 

ffs - I was told this would fit my car my ICP!
I just really hope it has not caused any major damage to my engine - particularly the head gaskets.

It does say on that advert for all Subaru header tanks

Thank you

 

ICP telling me that cap should work fine mate. Not quite sure how when the metal valve under cap does not move

 

As per Merlin that cap only has pressure release and not vacuum return and is only suitable for use on the actual radiator.

The 003 version has the vacuum valve as shown below

 

jesus, what have they sold me - thank you!
Could this have done any lasting damage
car never overheated since it was fitted

what symptoms would you expect to see of using this cap
glad I know now!

Prob explains my radiator blowing and hoses getting leaks under pressure

Should charge back the bits to icp

 

Symptoms would be as you have experienced -
Expanded fluid when hot not returning to system when cooled down.
Radiator hoses collapsing as system is under a vacuum when cooled down ( also means system is tight not drawing in air).
"Rad" cap is rated at 137kPa(1.37 bar) as compared to "std" cap at 110kPa (1.1bar) meaning the system has been running at a higher pressure.
An STi cap is rated at 1.3bar so not overly pressurised.

Get a proper expansion tank cap, refill the system and have the expansion tank half full to start and see how it goes.

 

 

Really depends if you want to run the system at a slightly higher than standard pressure (raises coolant boiling temp) - useful for a modded engine.
Also has the "bling" factor



But beware the fakes.......

 

 

I've got one of those caps on mine.

Although I do believe the standard cap is also 1.3 bar?

 

Now this is where you have to destinguish between radiator cap and expansion tank cap

108kPa (1.08Bar)


137kPa (1.37Bar)


88kPa (0.88bar)



Checking the JDM database it would appear that the '97 STi has the latter of the above three rated at only 0.88kPa

 

Ah right, knew it was one of them. So the rad cap is always 1.3 bar without relief and the header tank is either 0.88 or 1.08 bar with relief normally with the expensive STI pink header tank cap giving 1.3 bar.

Sorted!

 

Thanks guys.
Yeah my car had the 1.1bar cap as pictured above, so must have been changed at some point from the 0.9 one.
Spoke to ICP and ordered up an STI 1,3 bar one so happy days.

Anyone want a 1.37 bar RADIATOR cap for £10? lol