In my experience, "viton" or fluorocarbon seals don't hold up to hot water or steam. This was confirmed by discussions with representatives (including technical engineers in their compounding chemistry group) of the Parker O-ring company, among others. However, the Dupont sales guy who returned my call said otherwise, and that the problem was our not using the brand-name Viton(R) compound. Your mileage may vary, etc. etc. In my book, the best seal for hot water and just about anything that dissolves into hot water, is EPDM.
do you really mean "hot water" and 150 F = 65 °c ??
I think this temperature is no problem for any rubber, I remember that I put a "hot water bottle" from Natural rubber to the cold feet of my children to warm them.;-)
If it comes to 150°C and pressurized water or steam it is another story. Hot water alone is handled well by EPDM (ápplication e.g. radiator hoses in modern engines). You need FKM (fluoro rubber, e.g. "VITON(R)) only if you have this level of temperature and contact with oil either as traces in the hot water/steam or, what comes more often, on the other side of a seal e.g. in the engine between engine oil and cooling liquid.
Then you have to select the FKM carefully, because bisphenolic cure FKM has some limitations in hot water resistance because of the chemistry of the crosslinking system, not the polymer itself. There are two possibilites to improve: Use lead oxide instead magnesium oxide in bisphenolic cure (Cave: Lead is no longer allowed at least in car applications in EC) or use peroxide-cured FKM.
