1.6 TD - Pressurised Coolant System - Do I Fear The Worst?

[Gernster]

My Mk2 Golf c/w GTD 1.6 TD, ever since I have owned it (4 months) has had a high pressure coolant system.

The car does not use water, there is no water in the oil, and the car is not overheating (finally got my temp guage working and I'm lucky if it goes over the first white sector)

Ive done about 2,500 miles (4,000 km) in it now with no hassles, but regardless of how long you leave it (even overnight) when you take the top of the expansion tank, it blows water out under pressure.

I would usually suspect the head gasket, but I would also expect that it would have got worse until the car overheated/ siezed up!


Any things I could check or maybe its just a peculiarity of this engine type (RA with garret t3)

I was going to fit a new thermostat to see if that would get it running at the right temp, as on a long country road runing at 100kph the temp drops so much the heater starts blowing cold air!  But I dont want to overstress the engine if there is something wrong?

any ideas guys?

[Quantum TD]

There are really only 5 reasons you might be building pressure in your car:

1) Blocked coolant return line: the leader that comes off the top of the radiator (or in your case, it should be spliced into the upper hose) can get clogged. On some MK II cars, there is a restrictor in the return hose to the expansion tank. I've seen them get completely plugged.

To test to see if it's clear, take the cap off the expansion tank, start the car, and make sure coolant is running through the hose and into the tank while running. If not, then pull the hose and try to blow through it. If it's clogged, then use a drill bit to drill out the restrictor. Or, if there is no restrictor, then snake out the hose, or replace it.

2) Bad radiator cap. This is not a common problem,  but it can happen and will allow pressure to remain in the system. In fact, I think a bad radiator cap blew the head gasket on my old 4-runner.

3) Clogged radiator. It's hard to visually check this, but if your coolant is grimy and you've never cleaned it, then it may cause it. Usually however, a clogged radiator will cause overheat and then boilover: not just boil over

4) Head gasket. I feared the worst, but prayed for the best on a 1998 TDI I bought. It wouldn't overheat, temps were always low, but it would force out coolant at high RPMs. It would idle all day and not lose a drop, but under load, it would blow coolant everywhere, and the coolant was clean. So, you could have blown your HG (you say your gauge never worked?) and not known about it. Also, oil in the coolant is not the only way to tell if you've blown it. Like me, you may be losing pressure into the coolant system under boost. Easiest thing to do is a compression test to see what comes up.

5) Thermostat. They usually don't go bad. You can tell if it's bad by leaving the cap off the radiator and running the car up to operating temps (i.e. the fan kicks on). Put your hand on the lower rad hose. If it's still cold after about 30-40 min of idle, and/or the rad fan never comes on, then your thermostat might be stuck.

If it were mine, I'd start on the coolant hose. If it checks out, then do a compression test. If that checks out, the do the rest (check return hose, flush, new fan switch, new rad cap and new thermostat w/coolant).

[jtanguay]

does the car get up to temperature when idling?  heat out the vents when idling? let it idle for a while to get up to temp then try turning the heat on.  if you get heat then its the t-stat.  with a good flush & new coolant & t-stat, my car pumps out some good heat  

[Gernster]

thanks for the responses guys, ill check out the coolant hoses.

Its had  a new rad cap indirectly as I tried to fix the flashing low coolant led by swapping the expansion tank (didnt work, ive actually snapped a leg of the led now to stop it flashing  :lol: )

The car only gets up to just over the first wide white marker ( 1/4 way) when left to idel for a while, it blows warm when hot but on a run the temp drops off and it blows cold again!

[rubadubdub]

it blows warm when hot but on a run the temp drops off and it blows cold again!

I dont want to be the bearer of bad news but this is exactly what mine did prior to the headgasket blowing. I think theres another UK guy (lonewolf or something like that) who had this happen recently on a GTD and it was a HG problem too.

From what ive read there seems to be a pressure valve on the heater core hoses to stop it bursting under pressure. So after starting it blows hot but after driving a while the coolant builds up a head of pressure, the valve shuts and it goes cold.

[RabbitJockey]

sounds like a head gasket.  don't fear tho, its an easy job to do imo and can be done in a day easily if u have all the parts

[Vincent Waldon]

I get to do the heater core in my MK3 this weekend... would easily trade it for 3 head gaskets.   :roll:

[Gernster]

I'll take a closer look this weekend, cheers all.

Head gaskets don't phase me too much, but i still freak out on OHC engines, incase I dont time it up right, plus on this there is the diesel pump timing too!

Looks like that ahu tdi swap out might take place a bit sooner than I thought! (got my eye on a cheap seat toledo donor......)

[Vincent Waldon]

I'll take a closer look this weekend, cheers all.

Head gaskets don't phase me too much, but i still freak out on OHC engines, incase I dont time it up right, plus on this there is the diesel pump timing too!

Looks like that ahu tdi swap out might take place a bit sooner than I thought! (got my eye on a cheap seat toledo donor......)

Holler if you get stuck.

The most important safety tip of all:   TURN THE ENGINE OVER BY HAND a few revolutions before attempting to start it... that way if there's a problem you will discover it as a gentle clunk rather than a large BANG !!

[Gernster]

just to close this out in case anyone has similar issues, it was the heater valves (fitted to Mk2s to stop the heater Matrix blowing due to excess pressure)

replaced them and all the pressure problems have gone!

(alos realised my rad fan switch was faulty too!)

[jtanguay]

just to close this out in case anyone has similar issues, it was the heater valves (fitted to Mk2s to stop the heater Matrix blowing due to excess pressure)

replaced them and all the pressure problems have gone!

(alos realised my rad fan switch was faulty too!)

and also sounds like you could use a new t-stat (if your temps aren't holding at least half way on the gauge)

i didn't think it was HG myself...  otherwise you'd see some different signs, although it could have been a very, very minor HG leak.  i've had similar problems when my oil cooler went bad on me.  coolant & oil was mixing!  what a PITA to change with a/c  

[burnt_servo]

to go with what the other guys have been saying .
 after  awhile the headgasket sealing rings .... the circular metal rings that seal the head to the block on each cylinder .... eventually they develop metal fatigue on the edges and start to crack and either out fail , or slowly start to weep  presure outwards , many times into the cooling system .

at least yo have some time to organised how your going to fix your headgasket .

[Gernster]

cheers, I have purchased a new t/stat, but i reckon whilst its still running cool its not putting the engine under pressure. The heater now blows warm air so it will clear the screen!!

Hey I say if it aint broke don't fix it!!

[jtanguay]

it would be a good idea to flush the coolant system if you've never done that before... it actually turns acidic and starts to eat gaskets... and metal  :wink:  unless you're not using the green stuff of course... and what better time to swap out the thermostat???  :lol:

[arb]

Heater valves !!!  Cool !