Blowing coolant all over the bag

2001 TDI with Malone 1.5 and 520's. Coolant coming out around the reservoir only at highway speeds plus 120kmh. Is it the the head gasket or ? I've replaced the cap, thermostat and bucket to no avail.... Help

What's the recent history on the car? A little background might help.

Are you seeing air bubbles in the coolant?

There's a test kit that you can purchase that'll tell you if you have exhaust in your coolant: sounds like, however, it's almost certain.

No bubbles in the coolant. Everything is fine as long as I keep it under 120kmh. 430km on the machine. Timing belt and water pump last done at 330km.

Ground speed isn't the factor here, RPMs would be.

Any more to add other than just the TB job?

Has there been any overheating?

Not sure what behavior exists with bad coolant caps, but I know that one test is to loosen the cap to check for differences in behavior. Don't think this has to do with a bad cap; rather, I think that it IS a head gasket issue (early stages of breach/failure).

With the car up to operating temperature carefully loosen the cap.
Does pressure release? --WATCH FOR HOT A-F COMING OUT--
If not take the cap off and have someone start the car and bring the engine up to about the RPM you would have at 120kmh.
Watch if it starts bubbling and/or over flowing.
The test kit mentioned might be a better test.

I had an old diesel Mercedes do this. Under load, like going up a hill or driving fast it would pressurize the cooling system with exhaust.

In normal city driving it was fine.

Higher cylinder pressure was causing exhaust gas to escape past the head gasket, over pressurizing the cooling system.

One of the symptoms was that the upper radiator hose would be pressurized even when the engine was stone cold after being left overnight. Normally it would pressurize with steam, and then it would depressurize when it cools. When it gets pressurized with something that shouldn't be there, I guess it tends to just stay pressurized until it gets released by removing the cap or something.

Head gasket or leaking EGR cooler. If you don't have an EGR cooler, then, well...

sisyphus said:

Head gasket or leaking EGR cooler. If you don't have an EGR cooler, then, well...

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X2 head gasket. I had a slow coolant leak for a long long time. Then a buddy in Indianapolis said let me drive it: he stomped on it in every gear and the second time and the cap blew and the temperature spiked. Slow down and it was just fine, do it again and bang. New head gasket, ARP studs all is well.

I'm getting excited at the thought of tearing it all down. Might as well do the timing belt and water pump at the same time? Long life belt kit or ? Is it worthwhile to upgrade at this time with a performance camshaft?

advancewest said:

I'm getting excited at the thought of tearing it all down. Might as well do the timing belt and water pump at the same time? Long life belt kit or ? Is it worthwhile to upgrade at this time with a performance camshaft?

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Sounds like you have to much money in your pocket.

"430km on the machine"
This should be the 3rd timing belt for the car.
I would recommend getting the high mileage timing belt kit.
It adds a few other items s/a cam gear, motor & trans mounts and maybe a few incidentals.
I got mine from ID-Parts and installed it earlier this year.
Water pump and all rollers are a must, all included in the kit.
If you never did a ALH TDI belt you would need to either rent the necessary special tools or buy them. You -must- lock the cam and injector pump before taking the belt off.

If you want to do the cam you could.
To get the full performance you would also need get a tune to match the cam.
If you want to go higher performance a clutch kit on top.
You could easily go into the $1000 (US) point.

Sorry if I rained on your parade.