overheating problem?

[sluketic]

I posted a while ago about a 1989 mercriuser 4.3 alpha one overheating when idling and at low speeds, but ok when cruising. I was told to check water pump/ impeller in the outdrive. This morining I finally got inside to look at the impeller and it looked fine, no broken fins. I will replace to pump/ impeller but not sure if that is the problem. What else could be causing this motor to overheat?

Scott

 

[Haut Medoc]

Re: overheating problem?

Yeah but how pliable is it?......
It doesn't need to have broken fins to perform poorly.....
Old impellers wear & can have a 'set'......​

 

[sluketic]

Re: overheating problem?

It was stiff but still flexable. What is 'set'?

 

[sluketic]

Re: overheating problem?

Is there any kind of pump in or on the motor itself or does the lower unit pump circulate the water by itself?

 

[Haut Medoc]

Re: overheating problem?

It was stiff but still flexable. What is 'set'?

'Set' is when the vanes stay bent over in the direction of rotation.....
The engine does have a circulating pump....
It's right behind the pulley on the front of the engine....
Replace the impeller & see if that is the problem....

 

[bomar76]

Re: overheating problem?

Is there any kind of pump in or on the motor itself or does the lower unit pump circulate the water by itself?

The circulation pump is on the front of the engine, belt driven off the crank.
The water pump in in the lower unit of the outdrive.

(EDIT: Sorry, Haut, didn't see your explanation when I posted...)

 

[EastEnder]

Re: overheating problem?

I dunno if the smaller alpha drives have them, but on the ones hooked up to the 350s, there is a small rubber gromet that connects the water pick up from the drive with the transome plate. Take a look at the transom plate and see if its all swollen up. Replace the gromet, its a pretty cheap part. Thats caused a lot of headaches from people overheating after changing many waterpumps.