Hey all so I tried to post this before but I’m too new to add photos so here we go again. Sorry in advance if this is long but I need help. I bought a 1987 Four Winns Liberator 241 with a 454 mercruiser that has been bravo one swapped. I can’t post pics yet but I’m only familiar with the alphas so not sure if there were different years, models, changes, etc. with bravos and I think the stickers were replaced since there isn’t a serial number on them. So my issue is the engine slowly starts getting hot when I’m on plane running but doesn’t get hot when idling, low speeds, or on muffs on the trailer. It’ll get up to 160 and stay there until I hammer down. I have checked for bravo-itis the fitting looks brand new, the impeller in the sea pump is supposedly new and I pulled every hose checking for pieces from the old impeller or blockages. The oil cooler is also supposedly new and I checked it’s not plugged up. The thermostat housing is also clean and like I said the thermostat works. I pulled the upper risers and they looked good but haven’t checked the lower manifolds yet. I also ran a compression test it’s perfect and even across the board so not a head gasket. My last ditch effort was the timing since I read that can make these big blocks run hot and it didn’t change anything either. Only things left that I can think of are the lower manifolds or if the inside of the sea pump is scarred up. One guy swore I need the newer style thermostat housing to allow more flow but others said it doesn’t make a difference. I’m also sure it’s getting hot as I replaced the temp gauge and had a laser thermometer with me on the water. It does cool itself back down when brought to an idle too. Any other suggestions or something I might be missing? Like I said the bravo thing is new to me and any help is appreciated

It's possible that you could have a hose collapsing under suction from the sea pump. First thing though I'd do is replace the impeller and housing with OEM Merc. I'd also replace te Tstat with an OEM 140* Merc one.

JSpoon,

We took our boat to a service shop to have a new raw water impeller done. They called me up and told me the impeller hosing needed replaced. I told them to do it. When I picked up the boat, they showed me the impeller housing. The grooves the impeller had worn into it were impressive. Cooling was FAR better afterwards. A new impeller ain't much good if it doesn't seal well in the housing.

Also, as Griff said, make sure someone didn't replace the supply hose from the drive to the raw water pump with just "hose", without the wire wrap. It can collapse under load, and severely restrict water flow, but will run fine at idle. The wire keeps it from collapsing.

Thanks. Brad.

Juat to clarify, is this a raw water cooled engine? Or does it have an exchanger for closed cooling?

And when Griff says OEM merc, go to a dealer. Don’t buy the ones on Amazon. Never know what you are going to get with all the fakes.

Is the hose installed on the correct "fitting" of the sea water pump?

it’s a raw water cooling engine. There’s no cooler or system for closed cooling, it just pulls lake water and sends it right back out of the exhaust

it does have the right hose it’s a sturdy thick wall hose similar to my exhaust (through hull) thanks for the info that’s probably my next step is to pull the pump and check it out internally. The guy I bought it from said he put multiple impellers in it but never mentioned the housing itself

I use the hardin marine billet housing and oem pump. Housing will last forever and they cool a little better. I also carry a complete housing loaded with impeller and Vaseline ready to go. It is easy to cook the pump when flushing. If they run dry for 8 seconds the pump is done
.install a sea strainer with water hookup for flushing. If using the rubber clamp on drive, duck tape it and turn on water slowly, start engine and when its pumping crank water up. Watch the hose, you can collapse the hose. Most pump damage happens during flushing. I learned this hard way.

Is this a fresh water or saltwater boat?
if it’s being used in salt water, the water neck in the transom assembly could be collapsing