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Mercruiser over prop overheat?

XS POWER

Regular Contributor
Hi me mates got a 5.0 liter mpi that overheats when loaded he has spent a fortune on chasing this problem it will not hold plan in swell and lugs will this cause overheat ? 19 pitch bravo 3 400 hours thank you
 
I would look at the water neck on the transom assembly. They corrode and restrict water flow causing a high speed over heat. 19 pitch is not too big for a 5.0MPI B3
 
Cheers Jeff it's a 21cabincruiser prob over 2 ton wet, set up for fishing of shore it's a dog in the swell ,will not cruise on 15 to 18 knots,
 
Cheers Jeff it's a 21cabincruiser prob over 2 ton wet, set up for fishing of shore it's a dog in the swell ,will not cruise on 15 to 18 knots,


.. That would be what I call a "Boat Show Special".... a boat sold with the smallest engine that will move it to keep the sale price down... The P/O over propped it to try to get it to move and then dumped it when that didn't ( it never!!) work...
 
Thanks Bob, it does 40 knots on flat water till it sounds buzzer it's a re power and yes I think the po wanted to get all he could out of it, I like Chris thoughts on it will look at that for sure.it such a dog in rough water wants to do 10 knots or build to over 20. Cant get it to sit just on plane
 
Thanks to everyone for input it's going in for gimble bearing next week and he is going for a 4 blade 17 and a wing any other ideas with overheat besides pump thermostat usuall maintenance , thanks again
 
Running an engine in an "overpropped" condition forces the combustion chamber temps and pressure to run above "normal" limits...valve damage in inevitable. Over heat a possible immediate side effect.. The quick test for correct prop is to run the boat with normal load, mostly full gas tank... If the engine does not rev up to within the specified wide open throttle range, it is over propped. If it exceeds that range it is underpropped. There are some circumstances where engines are intentionally underpropped, but overpropping is NEVER ok.... For decent engine life do not exceed 80% of your observed max wide open throttle RPM for continuous operation, e.g. cruise.

For comparison, my boat (see signature block) is a deep V (22 degree dead rise, a real power suck) cuddy cabin, 4000 lb dry. I run a 15x17 3 blade prop. Cruises easily in Barnegat Bay's steep nasty chop @ 2700 rpm and 17 knots .... It would readily cruise at about 19-20 knots @ 3200 rpm, however, my wife does not like to get splashed by the occasional bigger wave. Running fast in large, longer period swells is often not an issue of power but rather the fact that it is difficult for a relatively short water line length boat to maintain a plane under those sea conditions. Planing, after all is when a boat surfs on its own bow wave. If you look at the design of the offshore go fasts, you will notice that they are all very long for their beam. If a boat's water line length is shorter than the distance between swells, the hull will tend to "hobby horse"... not ideal conditions for a hull to plane.
 
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Cheers Bob, this is same deadrise bertram design aussie built,being a half cab all the weight is aft adding to the problem.
 
Thanks mcomm never crossed my mind I have always used the stlngray whale tail but I will put it to him anything that helps is good.cheers
 
Cheers Bob, this is same deadrise bertram design aussie built,being a half cab all the weight is aft adding to the problem.


A big difference is that when Chriscraft built these, the engines are not right up against the transom, but are moved FWD about 4 to 6 inches by a long(er) intermediate housing ... If I have anyone other than my wife on the boat, I tweak the trim tabs down..

Actually, if Bertram had made a 23ft... this would have been it. Another difference, is that the hull is NOT a Hunt design, but rather a patented revision/improvement on the Hunt by Jim Wynn. He terminated the two innermost lifting strakes a couple of feet from the stern unlike Hunts original which went all the way to the transom.
 

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Nice rig Bob similar to my 19 foot bow rider no cab plenty of deck, I cant upload pitchers cause I am a computer retard,prob not PC .mates boat is a Caribbean reef runner if you get bored one day and want to Google. I got a 4 blade 15 pitch was thinking of chucking that on it to see what it does, what do you reckon?
 
Running an engine in an "over propped" condition forces the combustion chamber temps and pressure to run above "normal" limits... valve damage in inevitable. Over heat a possible immediate side effect..
Precisely!
That condition will also lead to very expensive detonation damage.

I got a 4 blade 15 pitch was thinking of chucking that on it to see what it does, what do you reckon?
In post #1, you mention Bravo 3!
I'm not seeing a B 3
4 blade set in a 15 pitch!
 
You can post pictures by clicking on the "insert image" icon located in the menu bar above where you're typing in the "Reply" box. If you count from right to left it is the third icon button from the end. This will open another dialog window that will ask you if you want to use a pic from your computer or from a URL link. If you choose "from computer" it will open a file browser and you simply pick out the one you want. Click "Upload File(s)" when you're done.
If you want to use a pic from the internet you must copy and paste the URL link into the space provided.
 
Adding a "wing" to the outdrive is no way to improve performance. Maybe those things help on a little lake boat outboard (probably not) but should never be installed on a Bravo 3. There's something going on with your friend's boat that is more than just prop. A healthy 5.0 in front of a B3 in a 21 foot boat should haul ass, at least on flat water. If he thinks it's a dog now, wait until he tries running it with that contraption on there. If it's the factory setup and it's not doing its thing then there are issues not being covered in this thread.
Overheating should never happen, even if one decides to flog it by running wide open all the time.
Could you please supply engine and drive serial numbers so that we can know exactly which units we are discussing?
When I google info for that boat I see only outboard powered ones. Is there a better link you could send the shows the exact boat?
 
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See post 2

The pinch connection used at the transom assembly where the outer and inner incoming water hoses connect is a horrible design. The aluminum around that area oxidizes and "grows" which collapses the hoses and restricts water flow.

That should be the first check and then move on from there.

Three issues for over heat.

1. Water IN issue, water hose kink/pinch restriction. impeller
2. Temp CONTROL issue, (thermostat, thermostat housing parts issue or corrosion issue, temp sender/gauge, wiring, circulation water pump)
3. water OUT issue, (elbows, possible manifolds but rare,)


Bravo three uses matched propellers, one is standard and the other is reverse rotation and are Stainless Steel.

No standard prop designs are used.
 
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I would like to thank you all for your input he got it sorted it was the transom restriction so free beer and fishing trip coming up for me, cheers
 
Thanks for getting back to the forum....not everyone does... Enjoy the beer and fishing trip... Here on the "Jersey Shore", its getting to be "haul the boat for the winter" time... Been a crappy October but it looks as if the wife and I can sneak a trip or two next weekend before hauling...
 
Nothing but heat, flies, and clear blue skies down here for a while Bob.

I will have Pol caballe BANGING when you get here jack .cheers
 
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