CHECK THIS OUT TOO>>>>Re: 4.3GL PEFS won't come up to Operating Temp - UPDATE
I too, have been living a nightmare with my 4.3GI (sorry dont know the designation letters but they are 1997 4.3 TBI's) on my 278 Four Winns Vista. Since I bought it this past February, it has never gotten up to temperature - or should I say, it WOULD get to about 150* degrees at idle but once I planed, both engines would drop back down to 100* or less. I have replaced the t-stats twice, flushed the lines going to the housings, ran the engine with the thermostats out to flush out whatever crap kept getting stuck in the thermostats and holding them open, etc..
Until this past week I finally took the t-stat housings out "again" and sure enough, in the little itty bitty bypass port on each housing, 2-3 little pieces of impeller blocking it!! I had looked in there before but not seen them; this time I used a flashlight and unscrewed the brass 90 degree elbow. That gave me a straight shot view.
Took the impeller pieces out, voila. Engines go to 150* degrees and STAY there.
What made this more confusing is I replaced the impellers and the ones in there werent missing any pieces. It was the impellers BEFORE those from the old owners that fell apart and circulated through the engines.
