Hi, our engines are gas, but I thought someone may know something. The heads, overhauled by Wartsila, is our 18V34 SG will run about 3000 hours and start leaking coolant (glycol-water) at the O-rings sealing the coolant at the exhaust valve seat. When we take it apart, the O-rings are red, and they will be cooked or burnt in places, and mostly hard.
We have asked Wartsila for a new material O-ring in a try to get a material which will last, and supposedly they came up with one. Any experience here?

I am not totally familiar with gas engines but from what you said I believe there is something more serious wrong in the cooling system other than wrong o-ring material. It sounds like there may be an underlying cooling issue and the exhaust valves are not being cooled effectively.
It may be possible that the cooling system is not effectively vented trapping air in the cooling system that collects in the exhaust valve cooling chambers or the cooling pump is not pumping a sufficient amount of coolant either of which could cause the valve cage to overheat cooking the o-rings especially if the engine is being cooled on a closed pressurized radiator type system.
If there is air in the system water pressure gauge will fluctuate when the engine is running. In order to insure that the system is venting properly I would check that all components such as vent lines and valves are clear and functioning properly and the radiator pressure cap if fitted is in good condition and functioning properly.
It may also be possible that there may be a chemical component or contaminant in either the water or the glycol that is attacking the structure of the o-ring. I would have the coolant tested to to see if there is an incompatible chemical component or outside contaminant such as bacteria in the mixture.

We have seen the same problems on some diesel engine applications. The problems was caused partially by temperature but also from additive used in cooling water.
We had special hi temp viton o-rings manufactured and delivered, and that resolved the matter. Have you checked the cooling water additive ?
Rgds Mikkel Elsborg

This is most interesting; I will attempt to contact you; otherwise, I would like more information.
We have to run glycol for freeze protection, and we use product recommended by Wartsila. Now they are questioning our product. Can you be more specific as to what was damaging the O-rings, and what O-ring we could try? We are pretty-much on our own with 6 of these engines. The glycol fouls the turbochargers.