Possible overheating? 1990 4.3L / Alpha 1

[toyotaspeed90]

the engine is a 4.3L Mercruiser.... it's a GM engine.... has Alpha 1 stamped on the carb cover

the boat it's in is a 1990 20' Bayliner capri....

I just 'purchased' this boat a few weeks ago... it was annually Winterized and Summerized by a local Marine Shop. The family owned it since new in 1990.

I called the shop who did the work and they gave the following reports:

-Bellows are showing wear
-Gimbal bearing is 'growling' (though, i've had it running and I can't hear anything I shouldn't.... and I'm also a little skeptical of the shop as the family I got the boat from is extremely well off and never did the work to the boat themselves... so the shop could have been over-exaggerating the problems to get work orders)
-Poor water pumping while idling but fine at running speed

I've had the boat on the water and I've been watching the gauge like a hawk whenever we stop. It seems to run great (quite quick for it's size), turns great, makes no noises, and no other mechanical issues.

However.... I'm no dummy when it comes to engines.... I am ASE certified and have previously been a mechanic at a local shop and currently work at a car parts store.... so I understand the possible dangers if it does overheat.

Now for the end of this rediculously long thread....

I do not believe it has a freshwater cooling system as it has a tank with coolant in it.... is this a correct assumption?

Is there any sort of pump that might be causing an overheating issue at idle other than the waterpump bolted to the block (because in a car i've never heard of an waterpump having problems with cooling at idle but no problems at running speed....unless it has an underdriver pulley on it which this does not).

Lastly, is the waterpump comparable to the GM 4.3 waterpumps found in s10's, jimmy's, blazers, and astro vans? It looks to be almost the same, but I'd rather have the parts before I start a waterpump swap and be sure I have the right one.

Thanks!

 

[Bondo]

Re: Possible overheating? 1990 4.3L / Alpha 1

If there's a Tank of Coolant,... It's called Freshwater Cooling........

It it's pumping Lake Water thru itself,.......It's called Raw Water Cooling......

With Either 1,...... There's a Waterpump Impeller mounted in your Drive that feeds the Cold Water necessary for Cooling........
After All,...... The Coolant needs Cooling too......

The Engines Recirculating Waterpump is comperable to an Automotive pump,...
Except it's build of Better Materials.......
And I Doubt it's your Problem,..........

More than likely,...... It's the drive mounted Impeller..........

 

[Don S]

Re: Possible overheating? 1990 4.3L / Alpha 1

If the bellows are showing wear, replace it. That is what keeps the gimbal bearing, the ujoints, and the front seal of your outdrive dry. It's a maintenance item as is the raw water pump impeller in the drive.
Bellows every 5 years, impeller every other year. During winterization, is when the drive is pulled, alignment is checked, ujoints lubed, gimbal bearing lubed and checked, etc.
As Bondo stated, if you have a coolant tank with a "Radiator" cap and antifreeze in it, you have a closed cooling system also called a freshwater cooling system.
The sea water (rather lake, stream, river, or salt water) is what cools the antifreeze by going thru the heat exchanger. Similar to a radiator on a car, but it's all done with water.

Here are some things you may be interested in.
Service manual for the outdrive:
http://www.boatfix.com/merc/Servmanl/6/6covr3.pdf

Can't help you with on online manual for your engine, there isn't one. You need Mercruiser manual #7. Might look at ebay.

Here is a link to a 2000 owners manual. The basics are the same, but not the technical stuff.
http://www.mercstuff.com/howdoi.htm

Here is one that just covers a lot of Alpha and Merc basic repairs and is really handy for the first time owners.