overboosting, loosing coolant, help please!!!
 

firstly i hope this isnt HG failure

my 95 sti is overheating now and then and only when stopped or moving slowly. its also loosing coolant, sumtimes pissing out of the overflow. i have brownish white bubbly stuff under the radiator cap and my filler tube by the battery is covered inside by a rusty colour substance which has run down the outside of it too. my radiator stays cool unless i pump the top hose which is hot, that then usually warms the bottom hose a bit as well as the top of the rad both of which are usually cold.

it is also overboosting, most of the time to fuel cut off.

i need to get it sorted, only problem is iv only got bout 300quid spare at the mo and i gotta use it daily for work.
iv been driving it like this for months now, wouldnt i have notice something major by now? it starts first time, warms up normal speed, idles fine, engine doesnt knock or anything, and heaters are blowing hot and cold as normal? only time i notice anything wrong with it is its rough on full boost and overheating now and then til i top up the water.
my mates reckon it could be something simple like an airlock or dodgy rad but with my luck with motors im thinking the dreaded HG.

any thoughts please?

Mine was like this and it was a head gasket failure. Not saying yours is defo. Might want to change your radiator cap first off as they are only a few quid on ebay.

just ordered new cap, jdm one rated at 1.3bar, only 6quid.

also anyone know if steelseal actually works?

with all those classic symptoms id say 90% head gasket failure,you might be lucky but im guessing not and it is the =dreaded head gasket,sorry

all the signs

overheating
sludge
boiling/overflow of coolant

i know its looking like bad news so i am preparing for the worst, have found headgasket on flat4online brand new for 140quid. do i need 103mm sleeved or 93mm? anyone know wheres best to get it done in south wales?

just thort i should also add, the oil is clean and so is oil cap.

AVOID flat4online !!!!!!!!!!!

as above avoid flat4online, as by the time the head gaskets come it will a antique:lol1::lol1::lol1:

lol no flat4online then. should i just buy one off ebay?

lots of specialists who advertise on here will sell you the correct gaskets for your needs and wont mess you round in the process, try in no particular order, rcm,zen,api,scoobyclinic

thanks mate, my over boosting problem apparently could be caused by my turbosmart dump valve, does this sound right? or possible?

Definately sounds like a hg problem :( not a cheap job either if the block is warped (advisable to have both heads skimmed or you could be paying for another hg job soon afterwards :()
As for the overboosting, what car, what year, what mods, what ecu? is it mapped?

Tony:)

Dave at API charges £700 + VAT (£805 before the year ends!) for a straight HG replacement (assuming no other work is required once 'in there'). This includes a very light skim of the heads'/block halves' mating faces (i.e. so long as it's within accepted tolerances) and a set of all-metal STi 3/4 HGs.

Also, I think WMS charge £700 ALL IN! to do the same work.

I'd defo get your system drained and refilled 'the correct way' to eliminate any possible airlocks before condemning the motor though.

Also, what about the operation of the stat and/or water pump, blocked rad, etc, etc...?

yeah, im gonna explore every other possible outcome before i jump in head first, im not the most mechanically minded person though to be honest, obviously hoping it is a simple fix but i am prepared for the worst.

its a 1995 sti redtop import, only mods as far as i know is hks airfilter and turbosmart dump valve, rest of the engine is standard with standard ecu, even standard exhaust.

:lol1:

liked that? lol

anybody wanna buy the bugger? lol

lol

just to let u all know its a 555 ltd, i know these are becoming quite rare so im gna do everything i can to keep it on the road!

BTTT

iv been driving it like this for months now, wouldnt i have notice something major by now? it starts first time, warms up normal speed, idles fine, engine doesnt knock or anything, and heaters are blowing hot and cold as normal? only time i notice anything wrong with it is its rough on full boost and overheating now and then til i top up the water.

not sure but I'm interested how this turns out as I'm having similar problems (no overboosting though) with my legacy. I've replaced the radiator cap and got an all-aluminium radiator to go on, just waiting for new hoses as the top hose split the other day.

Yeah, sometimes the gaskets only fail a tiny bit and therefore are fine under normal atmospheric pressure (off boost).

But is soon as you put meaningful boost through the motor, then this can cause the fracture to open out/lift. The boost pressure gets into the coolant galleyways, raises the system's pressure to beyond 0.9bar, so therefore coolant is forced past the rad cap and into the overflow tank, etc, etc...

This is exactly what happened to my old fibre composite HGs :(

water coming out of the overflow by the battery is a dead giveaway for hg failure. sorry bud. i would not keep drving it till its sorted, you could damage the bearings if the oil and water are mixing (depends where the gasket has failed).

well it does look like theres a very small amount of oil in the header tank so either oil is getting into coolant system or there was oil in there somehow to start with, im gonna bleed the system through 2nite and flush it all out and top up properly, then check after driving for a bit to see if there is oil there again. i have to drive it everyday to get back and forth work, not boosting is no fun!

oh i forgot to say, iv just run it outside work for 20 mins with rad cap and filler cap off, water came out the top of the header tank, but just a trickle, and the coolant level didnt drop in the overflow tank at all, my radiator stayed stone cold, the top hose was hot but the bottom hose was freezing. dont really know what this means coz the water in the header tank got hot enough to produce steam, why wouldnt the radiator get hot? fans didnt come on either but they have in the very recent past? im so frickin confused by this motor!!!

Make sure you fill the system so that you bleed air out of it!

Do a search; there should be lots of threads explaining the procedure...

Stone cold bottom hose will invariably mean an airlock in the system. Now that could just simply be a random airlock - see above on how to reinstate the coolant to eliminate airlocks.

Or it could be a blocked rad or, indeed, what you don't want... the dreaded HG! :(

Cheers joz, thanks for the advice, lets get the possible simple fixes out the way first 2nite then. ill be on later this evening or tomorrow morning with an update.