starboard engine runs hot under load any suggestions?

[vanman59]

1989 300 Weekender, 454 mercruiser, closed cooling system. started overheating last year. Here's what I've done:
1. found the left bank manifold had a whole in it at the #5 cylinder due to a leak between the riser and gasket, leaking and dripping salt water into the manifold directly into the #5 exhaust. Good thing the bottom of the exhaust port in the manifold was lower than the valve seat. This let salt water sit in the manifold until it rusted a hole in it. I replaced the left bank manifold only. I broke two bolts off in the head but luckily they stuck out enough to use break free and tap with a hammer and vice grips to remove the broken bolts. I am not to keen on replacing the outboard manifold just yet (bolts are very tight).
2. Replaced raw water impeller and housing. The impeller was good, impeller was not missing any fins and was still very pliable. Still overheated.
3. Replaced the circulating pump and thermostat with marine bi-directional pump and 145 degree thermostat. still over heating under load.

Here is where I am today: when we were replacing the engine circulating pump I noticed the coolant was black but didn't think anything about it. I was removing the right bank riser and noticed corrosion on the top of the manifold where the riser bolts to it. I took the riser off and it seems that maybe there could have been a leak between the manifold and gasket that let exhaust gas into the fresh water cooling system. My reasoning behind this hypothesis is the inside of the manifold is sooty due to running a little rich and it hit me that the coolant is black, and the manifold looks like it has been getting corroded due to a possible leak at the riser/manifold. Any suggestions would be appreciated.

 

[Stee6043]

Have you flushed the cooling system (heat exchangers)? Sounds like you've been pretty focused on the pumps and manifolds but the exchangers are also quite critical and can gum up or fail.

Another question - are the 145's correct for your engines or should it have 160's? 145 sounds coollddd....

 

[vanman59]

both engines run 145 degrees at idle. The port engine runs a little warmer at running speeds. I pulled the right bank riser and it appears as if the riser was plugged up. Not completely but pretty bad. I could see where it appeared as if the gasket could have been leaking between the gasket and manifold into the water jacket. i could also see signs of overheating in the exhaust hose also. I was just going to replace the manifold also but it looked good inside the exhaust cavity and the one bolt I tried didn't want to break loose and I didn't want to break any bolts off in the head. Plan- replace the riser gasket and run it.

 

[Stee6043]

both engines run 145 degrees at idle. The port engine runs a little warmer at running speeds. I pulled the right bank riser and it appears as if the riser was plugged up. Not completely but pretty bad. I could see where it appeared as if the gasket could have been leaking between the gasket and manifold into the water jacket. i could also see signs of overheating in the exhaust hose also. I was just going to replace the manifold also but it looked good inside the exhaust cavity and the one bolt I tried didn't want to break loose and I didn't want to break any bolts off in the head. Plan- replace the riser gasket and run it.

So no plans to flush the cooling system? You noted black coolant above. Sounds ominous.

 

[scoflaw]

Sounds like your issue won't be resolved until you take care of all the overdue maintenance.

 

[vanman59]

So no plans to flush the cooling system? You noted black coolant above. Sounds ominous.

when I pulled the engine recirculating pump the coolant auto replaced. I use the boat in a lake and pulled the strainers to clean them and there wasn't any debris in the strainers or hoses going to the raw water pump. The only thing in the engine is antifreeze and water. Anything I could find online indicated overheating under load was generally a manifold/riser issue. This I can see because I can putt around the lake with no problems. I'll let you know after this weekend and will flush everything I just fear having to get my big self into the bilge to disconnect hoses I cant even see.

 

[vanman59]

Sounds like your issue won't be resolved until you take care of all the overdue maintenance.

I am a newby boat owner so I dont know what maintenance is over due. I replaced the raw water pump (impeller was in great shape, pliable and nothing missing), all the hose are in good shape not to pliable or hard and cracked, new thermostat and water pump (I didn't think the water pump was bad but my son was insistent, the bearings felt a little rough, not loose or worn just not smooth like it should feel.

 

[scoflaw]

From what you've said, you need manifolds and risers. Weather that means removing the heads to get the bolts out or not, and they can be directly responsible for your overheat.

 

[Espos4]

View attachment 71783

This picture says it all.

 

[Ididntdoit]

View attachment 71783 both engines run 145 degrees at idle. The port engine runs a little warmer at running speeds. I pulled the right bank riser and it appears as if the riser was plugged up. Not completely but pretty bad. I could see where it appeared as if the gasket could have been leaking between the gasket and manifold into the water jacket. i could also see signs of overheating in the exhaust hose also. I was just going to replace the manifold also but it looked good inside the exhaust cavity and the one bolt I tried didn't want to break loose and I didn't want to break any bolts off in the head. Plan- replace the riser gasket and run it.

You're going to run that?

 

[joeyleggz]

What temperature are you seeing when you were overheating? Closed cooling engine thermostats are 160 ,raw water cooled engines are 145 my big blocks with closed cooling runs at 170 all day long

 

[vanman59]

Well here's where I'm at. Took boat out after cleaning riser up, filing surfaces flat and replacing riser gasket (solid one, fresh water cooled engines). All that has been done has helped. I could run the engines at 3,000 rpm and they starboard engine went to about 185 to 200 and the port stayed at about 160 or so. I didn't let the engine get any warmer and shut it down. After cooling down I was able to put around at about 1200 rpm with no over heating, it ran a little warmer than the port engine at about 155 or 165 on the gauge.
Next step Stee6043 has has suggested: I'm going to remove the heat exchanger and inspect and clean it and try to flush the cooling system, raw water and engine coolant. I still haven't replaced the right bank manifold, I might try pressure testing the manifold and see if it has a crack. the left one I had to replace due to the riser side of the gasket leaking saltwater into the #5 cylinder exhaust port and caused a rust hole in the manifold and leaking exhaust. The exhaust leak and overheating occurred together and started this venture.

You're going to run that?

For testing, yes. As far as the riser goes I cleaned it out, filed it flat and down to clean metal then reinstalled it with a new gasket. The overheat alarm doesn't come on and i can shut down the engine and run on one until time to dock.

 

[vanman59]

From what you've said, you need manifolds and risers. Weather that means removing the heads to get the bolts out or not, and they can be directly responsible for your overheat.

Everything I've read says that under a load overheat is caused by manifolds and risers too. I just know i'm gonna break some bolts and have to pull heads. I replaced the left bank manifold and riser already. I am going to flush the cooling system and inspect the heat exchanger first and if nothing found I'll bite the bullet and pull the manifold as much as it scares me to do.

 

[scoflaw]

Putting a torch to the bolts will help them break loose. I'd pull the HE and have it boiled out at a radiator shop

 

[blue#88]

I would highly suggest you look at your engine oil coolers or do trans coolers they both have heat exchangers if a portion of your walk water impeller found itself in line that would restrict flow, I've had it happen to me

 

[Stee6043]

I would highly suggest you look at your engine oil coolers or do trans coolers they both have heat exchangers if a portion of your walk water impeller found itself in line that would restrict flow, I've had it happen to me

This was a two year old post. The OP hasn't been around in over a year. I'm sure he figured it out...or sold the boat