Solution to Mercruiser Overheating Problem

[dwmackenzie]

Just thought I would share a simple fix to an overheating problem I had...after proactively replacing my manifolds and risers (an easy job) this spring I ran into overheating issues.  I checked all the usual items, impeller, thermostat, heat exchanger (my 6.2 MPI's are fresh water cooled), etc I found that I did not have good flow coming to the raw water pump.  Turned out the connections through the transom plate corrode and restricted the flow.  Ran fine at low speed but overheated when I would go up on plane.  Solution...plug the hose coming through the transom assembly and put in a through-hull that allows 1-1/4" hose to connect directly to the raw water pump intake (also installed a strainer).  Engine runs like a champ now!

[raybo3]

Hey dwmackenzie welcome to the RBO and glad everything worked out great..

[alswagg]

Hold on there.  You will now overheat your gear case, since you are not running any coolant through the gear case assy.  You could add a Y to your current set up and run sea water through the drive coolant line and also through the hull pick up.   If you leave as is, stock up on upper gear set and clutches.  Al

[dwmackenzie]

I had one mechanic mention that to me but then the marina that did the fix said that Mercruiser has approved this fix and even sells a block off kit to enable it all to work.....I also have a friend that has done the same work around to his boat...so I think I am good...I hope I am good.  Do you know otherwise?

[alswagg]

Merc does have a bock off kit, but you must also completely remove the water hose assy from the transom.  This is usually sold to house boats whick do not get on plain, and the drive is always submersed in water.  Drive is cooled by surrounding water.  On your boat the drive is only cooled by the water flowing throught he drive, while on plain.   Not really recommended since the Bravo drives have a tendensy to overheat and boil the drive oil.   A drive shower is now a must.    Al

[dwmackenzie]

Al, thanks for the info...now I am concerned and am checking with the marina that did the work.  You sound quite knowledgable in the space...did you find this out the hard way or are you a Mercruiser mechanic?

Also, why does the hose on the outside of the transom assembly need to be removed?  They did that in this case since the boat was out of the water and the drive removed at the time but I was thinking that when I did the other engine (which now I might not do based on your comments) I would simply block off the hose on the inside of the boat.

Thoughts?

[Dream 'Inn]

I would definitely go with what Al is stating.  Put it this way, he may have been the one that designed your boat.

[alswagg]

The reason you need to remove the hose from the transom assy is to allow water to self flow through the drive assy.  This will allow some cooling of the upper gear case.  I still would highly recommend installing a drive shower.   I have seen a fair share of Bravo Drives fail due to overheating.  Good luck   Al

[DaleM]

I'll never own an I/O without a drive shower.  Take Al's word for it, he's the MAN!!

[Dream 'Inn]

Now wait a minute here.  There are two stories going on.  Owning an I/O without a drive shower to me is fine.  If it is not running warm, and never ever seen any signs of running warm, no white chalk, not a loss of a drop of lube, then why mess with it??

Now, blocking the flow of water thru the drive, that will cause a problem big time.

[alswagg]

Bravo's will over heat on extended ong periods of high rpm, over 4,000 rpm.  Extended periods would be an hour or more at said rpm without slowing down.  On inland lakes this does not happen but on open water it is not uncommon.  Merc will not pay for the drive shower but I have gotten reimbursed for haul outs.  Simreck Halo Max is the shower recommended by Merc.   Al

[DaleM]

There are times I'll run 2 hours straight at cruise.  Had chalking happening on the 232 but once I read about drive showers I figured anything that keeps the drive cooler while running is a good thing...HEAT is bad for the lube and parts.  Dream, that's why I'll put a drive shower on any and all I/Os I will ever own.

[Dream 'Inn]

I agree that it is a good preventive measure.  I guess in the 4 years I have owned this boat I have never seen the chalky substance nor have I had to add gear lube in the summer.  & I do see my drives all the time, the boat is on a lift.  Heck, I even keep my drives shiny and waxed (a bit sickening I guess).  I also see many, many other drives on my marina since they are all on a lift, and I just don't see the chalk on them.  I guess most of us just don't cruise over 4k rpm, really.  I know I really don't cruise over it but do cruise at 3800 quite a bit.  I only have a few times thru the summer where I will cruise at 3800 3hrs or so, most of the time it's about 1-2hrs.  Things aren't all that far away when you are in the middle of the bay.

Again, I'm sure it helps, but even as the web site says that sells them, only a smaller percentage actually need them.  If I had the symptoms or drove my boat a lot at higher speeds, then I wouldn't think twice about it.