4.3 omc that overheats... Help.

[raytom]

Hey guy's new here to the site. Hope someone out there can help me. I have a 1988 4.3 omc cobra that burnt up the impeller. The impeller melted and did not break a part. So I have replaced the housing and impeller. Also I cleaned out the heat exchanger for the power steering. Last year I put a new termostat in (marine type). Took it out over the weekend and did fine until I had it out running about 35 or so. Then the temp creeped up. Did not hit the red but close. That was running for maybe an hour. Then it did the same thing on the way home. Got it out of the water and looked at the impeller and found that one or two fins on the impeller were turned in the wrong direction. I know I put it in right. I put it all back in with everyting in the right way and took it out again. Got home and the same thing. Anybody have any ideas on whats wrong.

 

[Gary H NC]

Re: 4.3 omc that overheats... Help.

Welcome to Iboats RayTom,
If a couple of fins were turned the wrong way when you removed it,are you sure it was put in with the fins bent in the correct direction to start with? It gets confusing putting them back together sometime.
Or maybe you have some blockage from pieces of the old impeller.
I always greased mine up when putting it back together.

 

[raytom]

Re: 4.3 omc that overheats... Help.

Thanks for the welcome.
You know I thought maybe I did put it in wrong but I checked the old one and also checked with the rotation of the shaft that turns it. As for pieces of the old impeller it really did not come apart it got hot and turned the liner and melted a little. I did not see any pieces missing from the old impeller.

 

[Gary H NC]

Re: 4.3 omc that overheats... Help.

You may try a water flow test,
With the boat in the water,remove the large hose from the starboard side of the engine water pump. Start the engine,at idle you should have at least a 2 to 3 inch high stream coming out of that hose.That will tell you if the impeller is pumping enough water.
Do you have a manual for that engine?

I would think the old one melted from running the engine without a water hose hooked to the drive..
Have you checked the screens on the bottom of the drive where the water gets pulled in?

 

[raytom]

Re: 4.3 omc that overheats... Help.

The old one melted form catching part of a plastic bag on the lower unit. I have checked over the intake for any blockage nonfound. What manual is good? I know the omc one is probaly the best but what is the next best. Kinda on a tight buget. I will have to try the water test. Thanks for the help.

 

[Gary H NC]

Re: 4.3 omc that overheats... Help.

In a pinch the Seloc Manual is ok..#3404 for your setup..
It covers a lot of the basic trouble shooting and service.
I know a bunch of people say that manual is crap but i have it and it does contain a lot of usefull info..
I know the original omc manual is well over 150 bucks
Look on ebay they have both sometimes...
I gave like 25 bucks for the Seloc...

Just looked on Ebay..look up item# 250015835043...8)

 

[Reel Poor]

Re: 4.3 omc that overheats... Help.

I would say you are installing it wrong, and the two fins you mention are the only two that either did or didn't flip to the correct rotation.

 

[raytom]

Re: 4.3 omc that overheats... Help.

Well didn't have time to do a pump test but did back flush the hose that runs to the thermostat housing. Looks like it had good flow to the impeller. Also ran the hose threw the exhaust maniflods. both had good flow. Would the fins flip with a blockage in the intake of fresh water or would it be something that is after the impeller. I did install with all fins in right direction.

 

[Gary H NC]

Re: 4.3 omc that overheats... Help.

I would think if there was a blockage it would just run with the impeller dry and ruin it again..
The only way i know of any of the fins flipping is if it was put in the wrong way....mmm a dilema..:%