Mercruiser 5ltr mpi

[Inboardfun101]

Hi everyone new to the forum in need of some guidance,

The engine is a mercruiser 5.0ltr MPI brovo 3 leg in a very tight for space Bayliner 245,


Currently experiencing cooling issues, I’ve been trying to get it to run on the genuine stainless pin quicksilver flush muffs, the engine has had a new impeller, circulation pump, thermostat, I didn’t run it till the overheat alarm sounded. all hoses appear to be in good condition non split or bent to restrict water flow.

Engine has been in a winterised state for 3 years All blue bungs are in.

[tkeithlu]

Welcome to the forum.

This is a heat exhchanger rig, right?

If so,you've got circulating raw water, circulating coolant, and the transfer of heat from the coolant to the raw water. One of those three isn't doing the job. Circulating coolant can be prevented from actually circulating by the thermostat staying closed, but you replaced that. A pump failure is also a possible source, but you replaced that impeller, I gather. Raw water is usually a pumpissue, but you've replaced that pump, right?

We're getting down to heat transfer. That's often a problem of scale in the heat exchanger blocking the tiny channels through it. Have you determined that coolant and raw water both flow through it freely? Does it need to be disassembled and soaked in vinegar? Ditto with scale in the coolant. It can interfere with heat transfer from coolant to raw water.

That'sall that comes to mind at the moment. Dig in a bit deeper and come back with the finer issue if you don't find the solution. Good luck with it.

[Inboardfun101]

Hi thanks for your reply it’s a purely raw water cooled I have run it in a water butt and on genuine muffs and still nothing I can only do so much before the risers get hot and then carry on the next day to avoid get burnt the high hell, it’s had new impeller, thermostat,circulation pump, I’ve checked the hose going into drive shield not kinged or failed, I used to work for a main dealer so I’m not a total novis but this just baffles me.