Hi Guys,
Merry xmas and happy new year!.
Cant seem to catch a break with this boat (grrrr).
Even though it hasnt gotten to the state where it is overheating, on the last few trips that ive had the boat out, the has been rising ever so slightly with each trip. My temp gauge always sits dead on half, and barely moves regardless of wether im idling or cruising. The last few trips it has slowly crept up to the mext mark on the gauge (which is the three quarter mark). I know there are a million threads out there on overheating mercruisers, and ive certainly had my fair share of overheating, but im a little perplexed, and hoping a mercruiser expert might be able to lend some suggestions on anything else that miht be a "common" issue to these motors. If i search for Mercruiser overheating issues, all i find is references to things ive already swapped out for brand new parts, less than a year ago.
It is a circa 2003 5.7 Horizon MPI 300HP. The boat also has a Bravo 3 outdrive.
I do all the mechnical work myself.
Last summer (when i bought the boat), it overheated badly, every trip, and within a number of minutes. I narrowed it down to the raw water pickup hose that runs through the transom from the leg. Bravoitis i think its called!. I swapped this hose out myself, and this immediately fixed thie issue. Each trip after that saw the temp rising no further than half way.
As part of me chasing that issue, i swapped out almost every other main cooling system part in an effort to find the problem!. So im not sure what it could now be causing my temp rise. Again - this time its not actually overheating. It will happily cruise at 3500 rpm all day and not actually overheat, but it sits higher than it normally does. If i come back down to idle speed, the temp will return to normal.
1) Thermostat changed this time last year.
2) Temp sensor changed this time last year.
3) Both manifolds and elbows changed this time last year.
4) Both exhuast flappers changed this time last year.
5) Exhaust Y pipe removed and all old flapper removed - again this time last year.
6) Raw water impellor and housing changed this time last year.
7) Entire cooling system taken off, flushed, and all old impellor pieces removed - this time last year.
8) Engine coolant drained and flushed this time last year (coolant level is fine).
9) Serpentine belt is tight, and not slipping)
10) Engine circulating pump has not been changed (i dont feel as though this is the issue)
11) Pickup hose running through transom changed this time last year.
12) Power steering and fuel coolers both removed and checked for blockage this time last year.
13) I have compression tested the engine and results are satisfactory.
14) Engine does not loose coolant.
Yesterday i pulled the raw water pump just to check that it hadnt deteriorated, and it was still in pefect condition, and has not hardened at all.
I run the boat in port philip bay only, and always flush fully for about 5-10 minutes are every use. I also start and run the boat (using earmuffs) each few weeks at home.
I am just about to buy myself a rinda scan tool, but unfortunately dont have it yet.
So - thinking about it
1) The guage could be wrong (very doubtful that it would be, but dont have a way of verifying)
2) Strangely, the charging system seem to be behaving oddly. When i start the boat it will sit at about 11.5 volts (reading at the guage), and will slowly get to about 13.9 volts over the course of about an hour). Something in the back of my mind tells me that last year when one of my batteries died, the temp gauge had a mind of its own. Anyone else experienced anything like this? Might just be a coincidence.
3) Ive chanfed out pretty much every common cooling system pain points with news parts in the last 12 months.
4) When i flish the boat, i generally get more flow out of the starboard side of the engine when flushing. This is inline with the port manifold being significantly warmer than the starboard. Reading a few posts about this last year, this didnt seem to be an issue.
SO - throwing it out there for thoughts and suggestions. Am i missing something obvious here?
Many thanks
Dave
Merry xmas and happy new year!.
Cant seem to catch a break with this boat (grrrr).
Even though it hasnt gotten to the state where it is overheating, on the last few trips that ive had the boat out, the has been rising ever so slightly with each trip. My temp gauge always sits dead on half, and barely moves regardless of wether im idling or cruising. The last few trips it has slowly crept up to the mext mark on the gauge (which is the three quarter mark). I know there are a million threads out there on overheating mercruisers, and ive certainly had my fair share of overheating, but im a little perplexed, and hoping a mercruiser expert might be able to lend some suggestions on anything else that miht be a "common" issue to these motors. If i search for Mercruiser overheating issues, all i find is references to things ive already swapped out for brand new parts, less than a year ago.
It is a circa 2003 5.7 Horizon MPI 300HP. The boat also has a Bravo 3 outdrive.
I do all the mechnical work myself.
Last summer (when i bought the boat), it overheated badly, every trip, and within a number of minutes. I narrowed it down to the raw water pickup hose that runs through the transom from the leg. Bravoitis i think its called!. I swapped this hose out myself, and this immediately fixed thie issue. Each trip after that saw the temp rising no further than half way.
As part of me chasing that issue, i swapped out almost every other main cooling system part in an effort to find the problem!. So im not sure what it could now be causing my temp rise. Again - this time its not actually overheating. It will happily cruise at 3500 rpm all day and not actually overheat, but it sits higher than it normally does. If i come back down to idle speed, the temp will return to normal.
1) Thermostat changed this time last year.
2) Temp sensor changed this time last year.
3) Both manifolds and elbows changed this time last year.
4) Both exhuast flappers changed this time last year.
5) Exhaust Y pipe removed and all old flapper removed - again this time last year.
6) Raw water impellor and housing changed this time last year.
7) Entire cooling system taken off, flushed, and all old impellor pieces removed - this time last year.
8) Engine coolant drained and flushed this time last year (coolant level is fine).
9) Serpentine belt is tight, and not slipping)
10) Engine circulating pump has not been changed (i dont feel as though this is the issue)
11) Pickup hose running through transom changed this time last year.
12) Power steering and fuel coolers both removed and checked for blockage this time last year.
13) I have compression tested the engine and results are satisfactory.
14) Engine does not loose coolant.
Yesterday i pulled the raw water pump just to check that it hadnt deteriorated, and it was still in pefect condition, and has not hardened at all.
I run the boat in port philip bay only, and always flush fully for about 5-10 minutes are every use. I also start and run the boat (using earmuffs) each few weeks at home.
I am just about to buy myself a rinda scan tool, but unfortunately dont have it yet.
So - thinking about it
1) The guage could be wrong (very doubtful that it would be, but dont have a way of verifying)
2) Strangely, the charging system seem to be behaving oddly. When i start the boat it will sit at about 11.5 volts (reading at the guage), and will slowly get to about 13.9 volts over the course of about an hour). Something in the back of my mind tells me that last year when one of my batteries died, the temp gauge had a mind of its own. Anyone else experienced anything like this? Might just be a coincidence.
3) Ive chanfed out pretty much every common cooling system pain points with news parts in the last 12 months.
4) When i flish the boat, i generally get more flow out of the starboard side of the engine when flushing. This is inline with the port manifold being significantly warmer than the starboard. Reading a few posts about this last year, this didnt seem to be an issue.
SO - throwing it out there for thoughts and suggestions. Am i missing something obvious here?
Many thanks
Dave
