Hi there
During this year's bike maintenance, was time to replace the cooling mixture and check the system components, everything was ok but when reinstalling the thermostat found that the internal gasket (not the oring) had swelled and will not fit. The diameter had increased about 3mm, perhaps due to the cooling mixture components.
Searching on google found that by heating the rubber it would shrink, try with a heat gun and boiling water with no succes.
Finally baked it in the convection oven at 350ºF by around 30minutes (checking it every 5 not to burn it) and came out at original size without loosing flexibility nor distorted.
Hope this helps
Best regards
JA

good tip jap

funny enough im going into that area of the bike this week sometime

cheers

Brilliant work Japuentes!

Interesting solution JAP, when mine swelled (due to oil in the coolant......pumpseal failure), I cut about 1/4" out of the ring and superglued the ends together as a temporary measure.

Paul.

I did the same, sidecar paul. I cut it out till it fit decently well and then held the ends together with gasket maker while I put it in. I figure the gasket maker will fill in whatever gap is there and I'll be good to go till I get a new gasket