A couple of things . . .
- Pull the heater supply and return hoses off the engine and see if you can blow through them, just to make sure there isn't something blocking them and/or the core.
- Try the reverse and blow INTO the engine outlet port; maybe a piece of rust or other deposit in the water jacket shifted and is partially blocking the outlet.
- Check your tranny cooler on the raw water intake side to make sure there is no gunk like weeds partially blocking it. My heater was noticeably cooler last week and I discovered lots of weeds in there. Strangely, the engine temp still read normal.
I did the heater install myself last year and it works fine. I used the Y-adapter from SkiDim that was mentioned above and I get good heat at idle and great heat when under way.
"For every complex problem there is an answer that is clear, simple, and wrong." (Henry Louis Mencken)
2005 X2, Viper Red, MCX, OJ TZ-X5 prop, PPass, rear 750 sacs, KGB, IBS, Bennett Wake Plate, custom wake gate
(previous) 2001 X5, 1991 TriStar 190