Mercruiser 4.3 exhaust manifold overheating

[Ryon Porter]

I'm having trouble with my manifolds over heating. The motor is running at ~ 160 to 180 but the manafolds are getting so hot they melting the rubber boots that exhaust through the out drive.

This is an open system and has always been in fresh water. I've looked for a valve or an open drain somewhere, I know I am missing something this drive train has less than 20 hours on it. It seems like a lack of water running through the manifolds?????

 

[Don S]

Re: Mercruiser 4.3 exhaust manifold overheating

Have you ever replaced the raw water pump impeller?
What year, what drive?

 

[a70eliminator]

Re: Mercruiser 4.3 exhaust manifold overheating

I've seen late (retarded) timing cause the headers in my drag car glow red hot. If your manifolds and risers aren't restricted of waterflow and cooling is all in order then do check the timing.

 

[Ryon Porter]

Re: Mercruiser 4.3 exhaust manifold overheating

The vintage is 2003 it is a 4.3 LH with a alpha 1 outdrive this drive train has less than 20 hours on it. The impeller on the outdrive has never been replaced. I'm thinking the problem would be impeller rather than the water pump.

 

[a70eliminator]

Re: Mercruiser 4.3 exhaust manifold overheating

Have you ever replaced the raw water pump impeller?
What year, what drive?

Thats exactly it

 

[Ryon Porter]

Re: Mercruiser 4.3 exhaust manifold overheating

I think it is a 2003 it has less than 20 hours on it and I have not replced the impeller in the Alpha 1 outdrive.

Thank you very much for the replies

 

[Don S]

Re: Mercruiser 4.3 exhaust manifold overheating

The impeller is rubber, it takes a set after so long. Hours mean nothing at this point, the impeller is 6 years old. They should be replaced every 3 to 4 years.
The FIRST thing any marine tech will check with any overheat is the impeller. That's just the way it is. If it's ok, then you can start troubleshooting.
20 hours on a 6 year old boat means there has been a lot of setting around doing nothing. Use it, or loose it. is the saying that comes to my mind.

 

[JustJason]

Re: Mercruiser 4.3 exhaust manifold overheating

20 hours on a 6 year old boat means there has been a lot of setting around doing nothing. Use it, or loose it. is the saying that comes to my mind.

Absolutely agree. The worst thing you can do to a boat is not use it.

 

[Bondo]

Re: Mercruiser 4.3 exhaust manifold overheating

The impeller on the outdrive has never been replaced.

Ayuh,....

There's your Problem,....

'course,... Now you've got Damage Control to go with it,...
I imagine the Rubber Parts in the exhaust system are probably Burnt to a Crisp,+ will also need replacing,....
Atleast the shutters,.. Maybe more....

 

[Ryon Porter]

Re: Mercruiser 4.3 exhaust manifold overheating

Thanks for the feedback. Does anyone know where I find a schematic so I can determine what parts most likely got burnt?

I hope I did'nt cause too much damage...... The engine runs so good.

Thank you for all of your help so far

 

[Bondo]

Re: Mercruiser 4.3 exhaust manifold overheating

Does anyone know where I find a schematic so I can determine what parts most likely got burnt?

Ayuh,...

Factory Service Manuals are available up in the Adults Only sticky at the top of this forum...

 

[Ryon Porter]

Re: Mercruiser 4.3 exhaust manifold overheating

You guys truly know your stuff! Sure wish I could have met you before the test ride.

The impellar pump was bad which in turn caused a dry exhaust situation that cooked the elbows as well as the shudders.

Gaining wisdom is truly expensive .

Thanks everyone for your accurate responses

 

[jetta1.9]

Re: Mercruiser 4.3 exhaust manifold overheating

Ayuh,...

Factory Service Manuals are available up in the Adults Only sticky at the top of this forum...

Where is adult only sticky at the top?

 

[MPII]

Re: Mercruiser 4.3 exhaust manifold overheating

The vintage is 2003 it is a 4.3 LH with a alpha 1 outdrive this drive train has less than 20 hours on it. The impeller on the outdrive has never been replaced. I'm thinking the problem would be impeller rather than the water pump.

My understanding is that the impeller is supposed to be changed every two years or so? Merc. 4.3's are supposed to run around 140. A bad impeller would cuase a general overheat in the engine.