mercruiser overheat, still can't figure it out

[b0mbtrack]

Mercruiser 4.3l vortec. ser# OW001038

The engine won't overheat at an idle but once I bring it up the overheat buzzer goes up and the temp goes up. I then lower the rpms and it goes back to not overheating.

I changed my pump impeller which I do every year, and I took off the hose at the thermostat coming from the drive just to make sure it was getting good strong water and it was.

I changed my thermostat but my old one actually looked to be stuck open.

I pulled off one riser but it looked perfect in there, almost like new. The manifold looked great too. I do flush it every so often during the season.

I was thinking of pulling the drive off again and changing the pump again, maybe I got a bad one or something. I thought I would see what everyone else thought first. Should I go for the drive or take a look at something else first?

 

[Don S]

Re: mercruiser overheat, still can't figure it out

Have a look at this service bulletin. I would sure give the clear hose test a try.

http://www.boatfix.com/merc/Bullet/95/95_13.pdf

 

[b0mbtrack]

Re: mercruiser overheat, still can't figure it out

Thank you Don, I will go ahead and do that. One quick question, what is the purpose of step four where you insert the two pins to make sure the water pump top does not touch the drive shaft?

 

[Don S]

Re: mercruiser overheat, still can't figure it out

I don't have a clue why it would hurt to bump the shaft, but the pins do make it easier to line up the gaskets, plate, and housing and keeps everything aligned. I made the pins out of a couple of metric bolts with the heads cut off.

 

[b0mbtrack]

Re: mercruiser overheat, still can't figure it out

Thanks again Don. Sure enough it was the pump impeller which was strange because I just changed it over the winter. Or it was something else to do with the impeller as i just went ahead and changed the housing and everything too this time. Took it out for a spin and it ran fine. Thanks again. As far as step four on that bulliten, i usually use a couple of picks for it. I just thought it was strange that they said to use them to keep the housing from hitting the shaft, but who knows....