Overheating Manifold 1998 350

[yammyman]

I recently acquired a mercruiser. The engine serial is 0L037276. When I run it the starboard exhaust manifold gets too hot to touch, and the port exhaust manifold is cool to the touch. I took the starboard manifold and elbow off. I then seperated the elbow from the manifold. I found some light scaling. I cleaned the scale out with a pressure washer. I then used compressed air to blow out all the passages. Finally I put the water hose to the passages to make sure that there is no blockages in the passages.

I went test run it, and no changes. When I open the valve at the bottom of the starboard manifold the water coming out is very hot. The water coming out of the same valve on the port side is cold. I picked up the boat and went home.

Once home I disconnected the water hose at the thermostat housing and attached my water hose to the starboard manifold hose. I then verified that I had water coming out of the exhaust on the outside of the transom. I figure Everything should be good. I then put the ear muffs on the lower unit and start the motor. After a few minutes I can tell the starboard exhaust manifold is heating up and the port is not. Where do I go from here?

 

[Don S]

Re: Overheating Manifold 1998 350

Have you checked the raw water pump impeller?

 

[yammyman]

Re: Overheating Manifold 1998 350

Dang it. I kind of figured since I had good water flow at elbow drain that the water pump was good. I did order a new water pump kit the other day. It will be here in a day or two. I will get it on and see what happens.

 

[Bondo]

Re: Overheating Manifold 1998 350

When I run it the starboard exhaust manifold gets too hot to touch, and the port exhaust manifold is cool to the touch.

Ayuh,.... Water, like electricity, flows the path of least resistance....

V-motor exhaust manifolds, Never, Ever run the Same temps....

Because it's an Unknown, change yer Impeller....
Even if it don't Fix it to yer liking, it's most likely fine...

 

[yammyman]

Re: Overheating Manifold 1998 350

I will definitely put the new water pump kit. Next time out I will use a temp gun to see how hot the manifolds get. At what temp should I be concerned?

 

[dubs283]

Re: Overheating Manifold 1998 350

when you pulled the riser, did you check the flapper??

 

[Bondo]

Re: Overheating Manifold 1998 350

Once home I disconnected the water hose at the thermostat housing and attached my water hose to the starboard manifold hose. I then verified that I had water coming out of the exhaust on the outside of the transom. I figure Everything should be good. I then put the ear muffs on the lower unit and start the motor. After a few minutes I can tell the starboard exhaust manifold is heating up and the port is not. Where do I go from here?

I will definitely put the new water pump kit. Next time out I will use a temp gun to see how hot the manifolds get. At what temp should I be concerned?

Ayuh,.... I've never checked it, but I know that when the lower shift cable Welds itself to the y-pipe,....
It's TOO Hot....

Verify that waters flowin' from both sides, if ya can....

Which T-stat housing ya got,..??
Maybe, Possibly, there's a chunk of old busted impeller messin' with it's flows,..??

What motor, 'n drive is this anyways,..?? yer number don't mean a thing to me....

 

[yammyman]

Re: Overheating Manifold 1998 350

Dubs - I did not check the flapper. I don't know anything about them.

Bond-o - This is a thunderbolt engine with a alpha one gen II. My t-stat housing has two big hoses forward and the two smaller hoses on the back end. I did disconnect both of the thermostat to manifold hoses and started the engine for just w minute to check flow. Bothoutlets had good flow.

 

[yammyman]

Re: Overheating Manifold 1998 350

How do you check the flappers?

 

[Bondo]

Re: Overheating Manifold 1998 350

How do you check the flappers?

Ayuh,... They're in the Top of the Y-pipe,... Pull the next coupler hose, 'n you'll see 'em,...... Or not....

 

[dubs283]

Re: Overheating Manifold 1998 350

the reason i ask is if the flapper falls and gets lodged in the y-pipe, it causes a restriction for spent cooling water to exit

if so, it backs up into the manifold and heats up becuase it cant leave

if one or both sides are missing you gotts find it, get it out, and replace the flappers

 

[yammyman]

Re: Overheating Manifold 1998 350

Dub - I was this king something was restricting the water from exiting the manifold. I just didn't know what it could be. I will definitely look into the flappers next time I get to work on the boat.

Thanks for all the help.

 

[Don S]

Re: Overheating Manifold 1998 350

If the flappers blocked the water exit, you would have some serious running problems long before you had overheat problems.
It would also heat up both manifolds, not just one. There is only a single opening going out through the bellows.

 

[dubs283]

Re: Overheating Manifold 1998 350

not saying a complete blockage, just enough to cause the issue

 

[tpenfield]

Re: Overheating Manifold 1998 350

I recently acquired a mercruiser. . . . . After a few minutes I can tell the starboard exhaust manifold is heating up and the port is not. Where do I go from here?

I seems that you have not verified the water flow from the thermostat housing (?). That is probably where the 'great imbalance' is happening. Port is getting most of the water and starboard is not.