462624 heads wtih 346250 manifold

[sntrym95]

Hey guys (and gals),

Been a member for a few months, first post. I have a Mercruiser 350 in my boat, and I have been having a problem over the last year:

The boat will idle to 140 deg just fine. This is the temp spec'd by Merc. However, when I put a load on it (in gear), it will go to 170. It will run fine at 170 up to about 3600 rpm. Then it starts to heat up more. If I back down, it still heats up, unless I take it out of gear an send it 3000 rpm for a few seconds, then it cools back down to 170. It never gets back to 140. Also, I noticed Sunday when running it on the hose that it was blowing white smoke at 1800 rpm.

The reason I am posting in this forum is that the engine fits the years of these trucks, save for the cam. I don't have the block casting, but the heads are 462624, and the intake manifold is a 346250. I just tore it down to a short block today, and have a question:

Do the 624 heads have the same tendency to crack like the 882's? I know they are almost identical, except for the "ridge" and a lighter casting than the 882's.

What has been replaced so far:

Water Pump
Outdrive
Complete impeller kit in outdrive, including the base.
Thermostat (with new gaskets)
Temperature sending unit (it has also been lasered at 170)
All hoses have been checked for leaks, cracks
The power steering cooler is not blocking water flow

I should make note that it would start to overheat at 4000 rpm before I blew the outdrive last year. After blowing the outdrive, and overheating the motor, the above problem surfaced. The head gaskets look fine, no cracks, etc.

Any help would appreciated. I am taking the intake and the heads to a shop to get magged, so I'll keep you updated...


Sntrym