Pressurising Coolant.

[mcglynn]

Hi Guys, whats the most likely cause?

Don't think it's HGF as the car doesnt pressurise quickly in the morning, and never overheats. No contamination in the oil and doesnt seem to be any in the water either.

My thinking is;

the thermostat
the radiator

Reason being is the bottom of the radiator is cold after a run but the top is quite warm? Thinking blocked rad but is there any way to unblock, or is it a case of changing it?

Thanks.

[Uberderv]

Fooked stat? Dodgy water pump. ....

[mcglynn]

water pump was done with the belt not even 10k ago, surely it would overheat after a hard run with the pump goosed?

Car is stage 2 and is running 160+ bhp (dyno proven) so with the boot down I would have thought it would try overheat?

No signs of overheating at all but there is a big buildup of pressure in there, it overflows the coolant like crazy if I manage to get the cap off after a run.

Stat would be the easiest to replace probably.

[j_carter]

Can you let me no if a stat fixes it as i have the same issue but have put mine down to headgasket failure as ive had the excact same issue on a previous car and it proved to be HG

[jammapic]

Probably headgasket mate. Cylinder to water jacket sounds like to me.

Pop the cap off and fill the rad up to the top, run the engine and rev it and look for bubbles.

Also, smell it when you,pop the rad cap off and there's pressure, see if it smells of combustion.

JP

[madmadmax]

water pump was done with the belt not even 10k ago, surely it would overheat after a hard run with the pump goosed?

Car is stage 2 and is running 160+ bhp (dyno proven) so with the boot down I would have thought it would try overheat?

No signs of overheating at all but there is a big buildup of pressure in there, it overflows the coolant like crazy if I manage to get the cap off after a run.

Stat would be the easiest to replace probably.

if you are taking the cap off before it has cooled then it will overflow because as the coolant heats up it evaporates and builds up presser to reduce the boiling point

its if it overflows when the lid is on that's when you have a presser problem

[mcglynn]

will have to smell it and see, but theres no cross contamination of fluids, e.g. no mayo on the oil cap and no water drops on dipstick.

When running and the cap is off there doesnt seem to be any pressure when I hold my hand on it, just when I go for a run and come back and take the cap off again.

When the car has cooled and is restarted, I was always under the impression that if the HG is gone, when you pull the cap after a minute or so of running the expansion tank will have pressure in it, this isnt the case in my instance?

---

OK Just went out to the car and after it sitting up for a while it hadnt got any pressure in it (water was still warm to touch).

Started the car and ran/revved it a bit, no bubbles; the water in the tank was as still as could be.

The stat hadn't opened yet as the radiator wasn't warm, and the temp gauge was reading just over 70 Deg C. When should the stat open?

I'm really swayed towards a blocked rad/stuck stat. Can anyone confirm whether all of their radiator is warm after a run? (on a 306 hdi to keep variables down).

I know heat rises, but the bottom of the radiator is as cold as ambient temperature and the top is as warm as the coolant. Surely it should all be warm to an extent.

Cheers.

[Uberderv]

Think its 83degC the stat will open, simple test it to take it out and put it in boiling water to see if it opens.

[mcglynn]

After a spirited drive last night the stat seems to be working fine. Temp gauge rises to in between 80 and 90 and quickly drops back down again so I assume this is the stat opening and reclosing.

Swaying towards a blocked radiator as ive been told there shouldnt be any cold spots on it after a hard drive?

Seems to be either the radiator, the water pump or the head gasket.

What is the small black pipe on the top of the expansion tank for? from the radiator to expansion tank

[Jtrigga]

I had a similar problem on my old gti checked everything turned out to be the rad cap try that if you have a spare.

[Ricky]

Do you have any history of how often the coolant has been changed through its life?

[mcglynn]

The rad cap is hissing when it's on so maybe it is the problem.

No history of coolant changes really, its on its second engine which got a through cleaning through when fitted with rad flush, and has had a few changes since then along with a new water pump.

Its currently running water as I have only just replaced the black housing behind the water pump due to me being heavy handed and breaking it, but wouldnt have thought the water would cause said issues.

---

also felt the radiator at the top and its only hot at one side (passenger) and cold all the way accross the bottom.

Its also cold at the bottom pipe (drivers side).

Looking more like a blocked rad.

[deggerz]

Also sounds like a stat my temp goes up to around 83 then drops to 78 if that's any help to ya

[mcglynn]

its not the stat the hose from the stat housing to radiator is roasting hot & hard.

The bottom hose from the rad is cold as are parts of the rad

[jammapic]

Does it misfire when you first start it?

If you go out for a drive, get it nice and hot - switch it off and go to bed. Check if there's any pressure in the morning.

JP

[mcglynn]

No misfire bud, it was a bit lumpy before but had a bad battery. New battery and it turns/starts extremely easy.

[Kwik]

my hdi I just got had HGF. pressurising coolant and loosing it quite swiftly. wasn't too bad at first and a bottle of k-seal let me drive it for a few more weeks till it was done.

Get it sniffed tested and go from there

[mcglynn]

no coolant loss here which makes me wonder.

Hoping it's the radiator that's blocked, if not then its going to be a leak somewhere or headgasket.

[Kwik]

if you got a friendly local garage ask them to sniff test it for you

[mcglynn]

yeah man one of my mates is bringing the sniff tester and fluid home 2moro

[Kwik]

That will let you know for sure

[mcglynn]

yup, fingers crossed its not hgf.

Isnt overheating after hard drives etc so hoping its an easier fix.

[Kwik]

Doesn't hurt to get a bottle of k-seal from euros. Normal is cool no need for the hd one. Works different from radweld so it don't clog up system

[mcglynn]

Id rather find the cause of a leak/pressurising than add that stuff tbh dude.

It doesnt pressurise that much normally and if all is well it shouldnt leak lol.

Seems like an 'easy way out' that often fails or causes more hassle using those treatments

[Kwik]

I was on about after the sniff test if it shows hgf gives you a little extra time to sort it

[mcglynn]

ahh, I seee.

Well there are no ill effects as of yet if it is HGF except a hissing rad cap lol.

So if it is hgf ill drive it on

[Kwik]

That's how mine started just a hissing cap would bleed it and would go away for a couple of days and then start hissing again. Then started to pressure more and more.

Reason why I dismissed head gasket was no mayo in oil and no film on water. Only till I got it sniff tested did i say ok lol.

I would get it sorted if it is cause if left can cause hotspots that crack heads but what I say is subjective till you know for sure

[mcglynn]

well got the sniff test done yesterday & it showed as HGF.

Thinking now what to do, e.g total engine replacement, head replacement and new hg kit, or just hg kit and get mine skimmed/tested.

Any recommendations?

[Kwik]

I done gasket and got head skimmed and tested. Made sense cause my engine had only done 114k.

Plus a replacement engine may well have the same issue

[mcglynn]

Yeah talking it over with JP and think head skim and new gasket is the best bet.

Will be selling the car end of this year but I want a reliable car for trips I have planned over summer including FCS.

Any recommendations on what way to do the gasket? Easiest way to get the turbo off in the car etc? Cheers.