[whincup]

Ever since changing to the GTI engine in my sierra, i've had this drama. with the overflow bottle empty and the radiator full, once the cars running and gets to operating temperature (based on standard temp sensor as well as aftermarket measuring head temp) the overflow bottle fills beyond full and spits out some water. once the engines off and cools, it sucks all the water back from the overflow, but obviously some is lost from that overfilling and the radiator ends up not full. anyone else had similar issues? standard sierra overflow, and its definitely not overheating. my plan is to just fit a larger overflow bottle, but is that masking another issue?


bit of info on my setup in case it makes a difference: standard (new) stock sierra radiator; standard sierra hoses from radiator outlet to water pump; 28mm ID flexible hose from the engine outlet at the rear of the motor, to the radiator inlet. hose is marine exhaust hose, was recommended this by a hose specialist as it can handle the temperature and pressure, has absolutely zero expansion or contraction so no issues with it sucking shut or expanding from pressure.

[alien]

I had this issue on my g16 bottom end / g13bb top end - it was a leaky head gasket. Exhaust gasses going into the coolant galleries and pushing hot CO2 back up into the cooling system.

It was near on undetectable... even running a test on the coolant didn't show up the CO2, but taking the head off you could clearly see the little pathway etched in.

New gasket fitted and running great ever since.

[shandy92]

What rating radiator cap have you got fitted? try fitting a higher rating cap and it will hold the coolant in the radiator for longer so wont push as much out. how empty is the radiator once cooled down? it shouldnt be at the top of the filler neck but at the base.

Aron, normally i would agree but when the rad coolings down, it would draw in what ever has the least resistance so would normally be air (from in the cylinder). so the coolant gets pushed out by the engines compression (pressurising the entire system). Im not saying that it wouldnt be the gasket but it would be a last resort, it sounds like the system is staying sealed but just pushing to much out.

[alien]

Mine used to suck from the overflow - the gasket leak joined up cyl 2 & 3 via a coolant gallery. New rad cap was the first thing i tried =)

[whincup]

cap came with the radiator so is new. but it was an el cheapo ebay one, worth trying perhaps. i probably have to put in maybe 300ml? its a guess, never really looked at exact amounts

[damagera]

easy solution would be to put in a bigger bottle,,,but keep a eye on it .. just in case

[Gwagensteve]

I vote head gasket. For the cooling system to "push too much out" it's either getting much, much hotter than normal, or there's a huge capacity increase from a normal sierra. Personally, I don't buy that. My cooling system has enormous capacity (rear mounted radiator) and whilst it would fill a stock sierra tank, it works properly with a 75 series cruiser tank. 300ml beyond a Sierra tank capacity just seems far too much.

Steve.

[tonyevans]

Might I ask what happens if you do NOT refill it right up does it loose more or just stay at the same level? (In the radiator when cold)

[Gwagensteve]

good point Tony.

[tonyevans]

I only ask Steve because my wifes Searra does the same but then stays fine for months even in the summer months here.

[whincup]

tonyevans wrote:

Might I ask what happens if you do NOT refill it right up does it loose more or just stay at the same level? (In the radiator when cold)

its hard to say as i've been topping it up before most drives, but im fairly sure it doesnt go any lower. if it does, its marginal. i've been driving it around all day today, i'll drive for a bit tomorrow, then check it sunday, see where its at.

after that, my plan at this point is use a 2L water bottle cable tied in as an overflow bottle to test it. if that solves it i'll just get a bigger aftermarket or one from another model.

[alien]

That's really not a great solution... something's clearly up so why not try to fix it before it goes catastrophically wrong?

mine used to only push out half of the overflow. Past that the cylinders couldnt generate enough pressure to displace any more. I did however get bubbles coming into the overflow bottle when it was full and up to temp (through the overflow hose into the bottle). This only happened later on though (about 6 months after it started pushing coolant out) which is what made me act and get the gasket checked and replaced.

[hooki]

Check if there is a steady stream of bubbles coming through the radiator on cold start up. I'm also told that you will be able to smell exhaust gasses in the overflow bottle if it's the head gasket.

Those radiator caps that come on those cheap ebay radiators aren't the best quality, I would replace that and see if that solves the problem.

[MrRocky]

Stuffed or incorrect thermostat can cause overflow/rad issues
I know masterA on here swears by a specific thermostat for his gti conversions (genuine gti maybe ?)

[alien]

Once mine started bubbling into the overflow it smelt like petrol but only just. After a bit longer a thin oily residue developed inside the overflow. You couldnt see it but when you wiped your finger inside the bottle you could feel it.

[shandy92]

Also, has the coolant changed colour? When my block cracked it went from fluro red to darker/morone red.

[whincup]

no change in colour, no smell coming from the overflow, cant say for sure on the bubbles since its never full when i check it. cant remember what i did in regards to the thermostat... i think i left the one that was already in there. definitely no mixing of water and oil at this point. i dont think its overheating, ive got the standard and an aftermarket gauge both saying its ok. and it runs fine otherwise...

[alien]

Then just keep a really close eye on it until you do see symptoms... that's what i did and i got about 6 months out of it before deciding to have the gasket replaced - as it started to overflow the overflow at highway speeds - which not only meant coolant leaking onto the extractors for a nice steam show and smell, but engine temps started creeping up too.

Oh and i had to keep burping the cooling system as it would get an air lock in the thermostat! Easy done with the sensor screw at the top of the housing... but with a warm engine and a good bubble, be careful as boiling coolant WILL shoot about 2m clear of the engine bay and rain down on you =P lol

[whincup]

not so easy for me, my thermostats mounted sideways, at the back of the engine. cant simply bleed that bastard...