Wacky cooling issue.

[Mkos1980]

When ideling for a long time, 15 minutes or so minutes warming up or ideling for 30+ minutes up the river I notice my temp reallly falls off. When starting for the first time, it'll go to 145ish (142 stat) and then it'll fall like the stat is opening up but it falls all the way past 100. If i rev it to like 750+ RPMS's the gauge will move up to the 145 mark and stay there. If I go back to idle 500-600ish it'll instantly fall back down below 100. Anything above idle and WOT it'll stay DEAD ON 145 and when I get off WOT it'll bump to 150 then back to the 145. When the gauge reads below 100 the port side riser is warm but nothing to worry about. The starboard side is HOT. I cant keep my hand on the riser, but rev it up a tad both are equally warm. Thermo is new last year, Alpha impeller is new last year. Engine water pump is origional 20 years old. Exhaust manifolds and risers were replaced last year. Any suggestions? I would think it would always be at 145 no matter what. Its like a lack of water , but the engine never sees over 145. Thermo housing is the 4 port style, 2 to the manifold, 1 to the impeller and 1 to the circulating pump. Its not the origional 6 style.

I did however lower my idle speed this year due to adding a larger pitch prop. At Idle with the 23P it was moving pretty good thought small dock areas and I was hoping to slow it down.

1990 MerCruiser 5.7L 4bbl
1990 Alpha 1 Gen 1

 

[Mkos1980]

Re: Wacky cooling issue.

Any thoughts?

 

[Bondo]

Re: Wacky cooling issue.

When the gauge reads below 100 the port side riser is warm but nothing to worry about. The starboard side is HOT. I cant keep my hand on the riser, but rev it up a tad both are equally warm. Thermo is new last year, Alpha impeller is new last year.

Ayuh,... I really don't see a Problem,... Although it's rather Odd acting,...
I'd probably drop the drive,+ have a peek at the Impeller anyways,... Maybe backflush from the T-Stat housing...
If Anything,... It might not be moving enough water at Idle.....


Oooohh,... Wait a minute,...

Thermo housing is the 4 port style, 2 to the manifold, 1 to the impeller and 1 to the circulating pump. Its not the origional 6 style.

I put a Gen.II motor in front of an Alpha 1,+ fought an Overheat at Idle for Years.....
Til I discovered the lower water flow of the Alpha 1 "Requires" the Check-balls in the T-Stat housing...
When I switched to the Check-ball housing,... My Overheat at Idle issue went away.....

Good Luck,+ Keep me posted,....

 

[Mkos1980]

Re: Wacky cooling issue.

I just switched to the 4 port recently LOL. Hmm. Why did I sell my 6 port bugger?? lol.