Mercruiser 120 - water shoots out exhaust manifold wrong way

[Mercruiser 120]

I have a 2.5L Mercruiser 120. It would over heat if I run at speed, then I could slow down and it will cool down, so I idled at the dock, tested the flow coming from the transom, loads coming in. Then I took the hose that dumps water in the manifold from the thermostat housing and water would spout out there. I thought it was the manifold so I had a newer exhaust manifold at home. New gaskets for the intake and the manifold. Same problem. How is exhaust getting in where only the exhaust is supposed to be

 

[GA_Boater]

How is exhaust getting in where only the exhaust is supposed to be

This is confusing.

Have you looked at the thermostat? If it's not opening at temp, the motor can overheat at higher RPM's, yet cool down at lower RPM's when the thermal load is less.

 

[Mercruiser 120]

I checked that but even on start up before the thermostat would be open, water from last ride spits out the front of the exhaust manifold. I’m worried if water is mixing with exhaust before usual(downswipe of the riser), that water is going to get in the cylinders through the exhaust ports/valves.

 

[Bondo]

How is exhaust getting in where only the exhaust is supposed to be

Ayuh,....... I would hope yer gettin' only exhaust from where the exhaust is supposed to be,.......

I'm guessin' you mean yer gettin' exhaust from the water port,..??..??

If so, did you inspect the exhaust shutter when ya changed the manifold,..??

If not, they may have burnt up, 'n fallen into the down-pipe causin' excessive back pressure,.....

You would get some exhaust at the water port anyways, as with the hose off, the exhaust pressure would be higher than the zero water pressure in the manifold,......
The 2 are common at the aft end of the elbow/ riser,.....

 

[Mercruiser 120]

When I had the riser off I looked down the rubber boot and moved the exhaust flapper it moved, the rubber was intact and looks like bird wings but folded down toward the transom

 

[Bt Doctur]

If your on land and this happens your exaust is blocked with something
If it happens on water the pressure from the exaust is pushing back up the exaust creating a positive pressure to force water and exaust gas out the port where the hose goes
Your exaust does mix with the water leaving the engine at the bottom of the exaust elbow

 

[Mercruiser 120]

I’m going to try to dump a pail of water down the rubber boot that connects thevriser where the water and exhaust mix and see if the water vacates through the exhaust tube then through the transom then through the bellows through the prop

 

[GA_Boater]

It will run right out.

 

[Mercruiser 120]

Even if there is a blockage

 

[GA_Boater]

Even if there is a blockage

Yep. The motor runs so it isn't a complete blockage, if there is one.

Has the impeller been changed lately? If not, you can check for a blockage while changing it.

 

[Mercruiser 120]

The impeller is new and the water in rate is great. I am having the overheat issue from anything on plane to full throttle. The exhaust manifold was hot as well as the riser and then when I took the hose off that puts cold water in the manifold off, hot gas and water spouted up about 4 inches, then again and it was hot. The hose I undid was putting cooler water in the bilge of the boat, which was good I wanted to see that. So I thought the exhaust manifold was cracked so I replaced it. Same thing this morning.

 

[Bt Doctur]

might be a clogged elbow causing all the trouble, I would put a funnel and hose on the manifold fitting first to see if it will flow freely, by that I mean as fast as your pouring it in the funnel