Thanks guys. The water temp is fine, stays between 80-85 under all conditions in cool weather. Thermostat replaced last year (old one did stick open). Hint, always buy the slightly more expensive thermostat with the thicker housing!

I cranked her up in the garage this morning (30 degrees) and let her warm up.
Heater came on as it should, after about two minutes (when water temp reached 35-40).
I stuck a thermometer in the side vent, turned the temp wheel up to 85F, and let the engine run until the water reached 80C. The air temp only got to
75F. So, I think it's not doing so well at low speed either.

I think the monovalve is a good suggestion. It's been 10 years since I replaced it. But logic tells me if it's torn then it would allow hot water flow all the time, rather than impede it? But, I know these things are weird.

Heck, I'll just do the mono kit, and maybe also take out the auxillary pump motor and clean it up and fuse it.

Funny thing; my wife still refused to drive the new Caddy SRX on this cold morning. It has remote start that even preheats the seats & steering wheel. But she loves the old Benz. (maybe I should have bought 12 old Benz's instead of the Caddy - Ha).

DG