Mercruiser 5.0 cooling question

[ljs22]

I am chasing the usual overheating issue in my Mercruiser 5.0 Alpha 1 Gen 1 with SN OA623969

It is the open open cooling system with the check balls.

I am trying to diagnose as much as humanly possible in the driveway since it is a 2 hour drive to any water big enough for this boat.

When I put water into the check ball hose to the top of the manifold it just pours out the hose that goes to the bottom of the manifold even if I hold them over the risers. Would this indicate the riser is crudded up or is it that much easier for the water go there instead of through the riser and out the back?

 

[Bt Doctur]

Re: Mercruiser 5.0 cooling question

http://www.boatfix.com/merc/Bullet/81/81_14.pdf, this has flow diagrams.
http://www.michel-christen.com/ExhaustElbows.pdf, riser cutaways

 

[ljs22]

Re: Mercruiser 5.0 cooling question

I think I may have found the issue. When I was replacing the entire raw water pump in the leg I found half a dozen Zebra Mussels behind the intake grills. I didn't find any in the water pump housing, thermostat housing or the steering cooler. I Will keep my fingers crossed on this one. Sound plausible?

 

[ljs22]

Re: Mercruiser 5.0 cooling question

What should be involved in the thermostat replacement on this engine? The diagrams I have looked at show 2 gaskets, a stainless steel spacer and a sleeve. My unit didn't have a thermostat in it so I don't have anything but the cover, a gasket and the housing. Did the 86 230 have all that stuff in it?

 

[ljs22]

Re: Mercruiser 5.0 cooling question

I just wanted to follow up on this since it seems to be a really common problem and few people ever post solutions that work. My problem was indeed related to the Zebra Mussels inside the intake grills in the lower unit. Once they were cleaned out and the unit was put back together there were no more overheats. The temp just climbed up to a certain point and stayed there. I can't give numbers since my gauges don't pretend to be accurate. They only have H and C. Just keep in mind that I didn't notice the Zebra Mussels in there until I was replacing the entire water pump assembly. They were right up against the bottom of the lower water pump housing. I am sure if I had used a flashlight and looked inside with the plastic grills removed I would have probably seen them. I would have still replaced the pump though since you would have no idea if any had made it past the pump and attached inside the water tube.

Hope this helps someone!