Cooling circuit over pressure but headgasket ok

[aduret]

Here is my problem: I was driving my vanagon 89 1.6TD on the highway a couple of weeks ago when the belt of the alernator and water pump broke. I stopped as soon as possible. My engine was relatively hot when it happened.

Since then, when I drive my van more than 30minutes, I have overpressure in my cooling circuit and cooling liquid coming out from the expansion tank via the cap. My engine is not overheating.

I went to my mechanic; he made all the tests to check wether the headgasket was leaking or not. He found that the smoke test in the liquid circuit was negative. Moreover he puts some pressure (>3bar) in the liquid circuit; it seems the circuit has no coolant and that no water enter into the cylinders (no white smoke after the pressure test in the exhaust gas).

So we have all the symptoms of a headgasket problem but after carefull investigation, it seems it is not that. I really dont understand what could cause this problem if not the head gasket. I would like to avoid changing the head gasket and have the same problem after. Anybody has any suggestions? Could it be the water pump?

Thanks in advance for your help.

[CoolAirVw]

Since then, when I drive my van more than 30minutes, I have overpressure in my cooling circuit and cooling liquid coming out from the expansion tank via the cap.

Get a new cap?

Actually if you have overpressure its probably a head gasket.

[rsxsr]

That sounds like a solid test to see if coolant is leaking into the cylinders. Remeber though, if the head gasket is leaking compression into the cooling system, the pressure would be 390 psi plus. It could be such a slight leak, that your test may not give you the result you are expecting. I agree the cap should be pressure tested. You should also be able to run the engine down the road with the cooling system pressure tester on the tank and see what pressure is forming in the tank. I am also assuming the cooling system is properly bled. While I realize your gauge says the engine is not overheating, idling does the radiator fan eventually come on? Sorry about the belt failing. Bummer

[stopping]

yes what he said.... bleed the system according to the insane techniques on this forum... but consider: 3 bar is nothing not a test for a head gasket try a test of 300 bar or 400 bar then we would talking about load conditions..... also you said belt not belts.....is your belt/ pulley arrangement stock? The WP might be turning too slow or slipping..... other considerations....combination of events: bad rad, timing too advanced, pinched coolant hose (especially pinched by front spare tire), the old rusted steel pipes might be blocked or really slowing things down. Then there is the crazy notion that your thermo is not being heated properly... ie: temp of exp tank not engineered properly ... (using hoses from a non TD machine).