aaz building pressure in the coolant......STILL!

[giulianot]

hello all,
 My brother has a mk2 gti with a aaz swap in it.  Just last week it started building up pressure in the coolant system making the rad hoses go rock hard. he removed the t stat and had the same problem. So i advised my brother that he most likely had a blown head gasket and he wa leaking compression into the coolant. So we pulled off the head and noticed some big cracks fro the pre cups tho the vales. I told my brother that the head was probably no good any more so we decided to put a different used head on. We had 0.011" machined off the new "used" head to clean it up a bit and remove some pitting. We installed the new head and now the the engine is still building excessive pressure in the coolant  does anyone have any clues to what it could be.  Hes still driving with no t-stat in,well install a new one tonight and see what that does.

[Smokey Eddy]

there will always be a lot of pressure in the hoses. Rock hard hoses isn't uncommon...


It's when it gets so great that your expansion tank can't hold the pressure. I'm assuming that's what's happening though. I wouldn't expect anyone to go through all that work just because of hard hoses?

That top rad hose will always be very hard...

Does he have 50/05 coolant in it? or straight water. Straight water will make HEAPS of pressure.

[dillenger1]

there will always be a lot of pressure in the hoses. Rock hard hoses isn't uncommon...


It's when it gets so great that your expansion tank can't hold the pressure. I'm assuming that's what's happening though. I wouldn't expect anyone to go through all that work just because of hard hoses?

That top rad hose will always be very hard...

Does he have 50/05 coolant in it? or straight water. Straight water will make HEAPS of pressure.

as well as freeze

[53 willys]

cooling systems on the cummins diesels can make so much pressure that it will blow the freeze plugs out of the block!!
high reving water pumps make lots of PSI......I think I would worry if it is spewing coolant out the bottle..other then that hard hoses are normal....

[Smokey Eddy]

I wouldn't expect anyone to go through all that work just because of hard hoses?

[commuter boy]

You didn't re-use the old head gasket, did you?

[8v-of-fury]

I wouldn't expect anyone to go through all that work just because of hard hoses?

[giulianot]

ok my bro came by after installing new t-stat and i witnessed it myself tonight, Under light load the engine stays at normal operation temp, good coolant flow through the rad and heater core. Once  you start to drive the car hard and bring up the revs and put the engine under load, the coolant all boils over and spills out the rad cap and no heat  out of the heater core and the temp gauge skyrockets :?: pull over and wait till the steam settles and put some more coolant in and drove it home. Then we let it idle there with the rad cap off and it circulated fine through the hole system?

MY only guess at this point is maybe his lower rad hose is collapsing under high revs and he is loosing circulation? any other guesses? were putting a spring in the lower hose tomorrow

[jtanguay]

ok my bro came by after installing new t-stat and i witnessed it myself tonight, Under light load the engine stays at normal operation temp, good coolant flow through the rad and heater core. Once  you start to drive the car hard and bring up the revs and put the engine under load, the coolant all boils over and spills out the rad cap and no heat  out of the heater core and the temp gauge skyrockets :?: pull over and wait till the steam settles and put some more coolant in and drove it home. Then we let it idle there with the rad cap off and it circulated fine through the hole system?

MY only guess at this point is maybe his lower rad hose is collapsing under high revs and he is loosing circulation? any other guesses? were putting a spring in the lower hose tomorrow

your putting in one of those hoses with the springs?  good idea.

[FoXBoXRaCiNG]

Did you spin the crank when you had the head off to check the block (cylinder walls)?

[zukgod1]

My money is on the head gasket or worse, case cracked head/block.
Head gasket more than likely.

[jtanguay]

hello all,
 My brother has a mk2 gti with a aaz swap in it.  Just last week it started building up pressure in the coolant system making the rad hoses go rock hard. he removed the t stat and had the same problem. So i advised my brother that he most likely had a blown head gasket and he wa leaking compression into the coolant. So we pulled off the head and noticed some big cracks fro the pre cups tho the vales. I told my brother that the head was probably no good any more so we decided to put a different used head on. We had 0.011" machined off the new "used" head to clean it up a bit and remove some pitting. We installed the new head and now the the engine is still building excessive pressure in the coolant  does anyone have any clues to what it could be.  Hes still driving with no t-stat in,well install a new one tonight and see what that does.

the motor needs the t-stat installed to effectively cool it.  without the T-stat, the coolant flow isn't efficient, and will give you trouble.

the used head that you had machined should have been pressure tested.  it's cheap insurance to avoid doing all the work required to clamping it down, and then removing it again when you find out its bad.

as stated above, did you install a new head gasket, and new head bolts?  what procedure did you follow?  did you torque the head bolts in sequence? not to sound like a dick or anything, but the more info you provide, the better the answers you will receive from the more experienced members of this forum.

libbybapa does have a good suggestion about the rad cap... and they're dirt cheap.

[53 willys]

ok my bro came by after installing new t-stat and i witnessed it myself tonight, Under light load the engine stays at normal operation temp, good coolant flow through the rad and heater core. Once  you start to drive the car hard and bring up the revs and put the engine under load, the coolant all boils over and spills out the rad cap and no heat  out of the heater core and the temp gauge skyrockets :?: pull over and wait till the steam settles and put some more coolant in and drove it home. Then we let it idle there with the rad cap off and it circulated fine through the hole system?

MY only guess at this point is maybe his lower rad hose is collapsing under high revs and he is loosing circulation? any other guesses? were putting a spring in the lower hose tomorrow

sounds almost exactly like what mine was doing when my HG was blown......
check the easy stuff first..like the cap.

[g-spec]

Sounds exactly what mine was doing.....city driving and idle was fine.....once you took it on the highway or higher revs it would boil over and spew coolant thru the cap. Turned out it was the head gasket only after 8000 km after doing it. Trying to diagnose it changed out the t-stat, rad, cap....until finally took the head off and cyl number 1 had tiny marks of coolant leaking in.....couldnt even tell by looking at the headgasket.

[arb]

If it is building excessive pressure a simple cause could be a faulty expansion tank cap.

Andrew

This cap is our pressure regulator. If it is a 15 psi cap, it will vent if the pressure exceeds 15 psi. Hard hoses or not. Like Andrew said, replace the cap. Some shops have a cooling system tester that also will test your cap. You pump air against the cap until it vents. The pressure gauge will tell you if your cap is working correctly. Without a gauge, how could you be sure you had too much pressure in your system ?