Bravo 3 Cooling


H

HappyKamper

New member
I have a 37pc with 496 mercs with Bravo 3 drives. In my waters everyone puts thru hull raw water pick ups with a sea strainer.
The outdrive pick up is closed off at the transom, allowing the drive to pick up water and expel it against the transom exterior.
In my case I have the thru hull "T" to the drive. Having both pick ups bringing in sea water. My problem is the outdrives are over heating.
My mechanic has seen this plumbing arrangement many times with no issues.
Does anyone else have outdrives with thru hull pick ups? Does anyone else have a problem with outdrive overheating?
We have a lot of seagrass in our area. The thru hull pick up with sea strainers prevents engine overheating.
 
I don't have thru hull pick ups, but was just curious how you became aware of drives overheating.....I have also heard of others with the "T" arrangement with no issues
 
The drive fluid would foam up into the reservoir. I drained the drive to see the oil was completely black after 20 hrs of use.
 
Do you have drive showers ?

Also, out of curiosity, was the "Tee" setup and thru hull pickups done at the factory ?? What year is the boat ?
 
Yes I have drive showers. The boat is '05. The thru hulls were not factory. In my area everyone makes thru hull pick ups with strainers
to avoid picking up sea grass that over heats the engines.
 
Is it both drives? I have seen the reservoir do this do to excessive heat. but not from being cooled, from a bearing going bad in the drive causing the heat. If its both drives then that might not be the case.
 
Yes I think both drives. Starboard is foaming and just blew out the top seal. When we drained the port, the oil was black.
We have the drive apart now. There is some unusual wear marks. I am trying to figure out if it's the chicken or the egg?
Is the drive overheating because of the method of cooling which creates the bad parts or is a bad part creating the over heating?
Since the other drive has signs of excessive heat, I'm thinking it's the method of cooling the drive.
In our area the method of cooling is used all the time. With the boat being a 37 pc, the design of using outdrives is at top of the design envelop
for outdrives.
 
I think a couple possible issues but need more info.

How are the drives refilled?
This question comes from not the filling from the bottom up, but is that it and then its installed or is something else done to make sure its full.

I'm assuming your using Merc performance gear lube, is this correct?

Which drive showers are installed?

how much time is spent cruising and WOT?
 
I assume the drives are filled correctly. In the spring they burp a little so I have to
add some gear lube to the reservoir.
I only use Merc lube.
I was cruising for 3 hours at 3600 rpm's.
I don't WOT.
 
Your issue is new, and have not seen before.

My thought as it could be a few things which might cause some heat issues. Merc says the drives should be drained and refilled yearly. Others do it every other year including my self. Running for 3 hours around 3600 should not be a major issue.

To one comment you made which gives me concern is "in the spring they burp a little" and the other comment of "starboard is foaming and blew out the seal". Both of these are indications to me that your drives are not full of lube. The lube once full should remain that way until damage causes and issue.

Some B3 drives have been known to leak for the prop shaft seal from exhaust fumes passing by causing a venturi effect. With the normal seal in good order this should not happen, but even Merc is replacing brand new seals to stop a leak. The yearly check should be able to see if any water has entered into the drive.

The best way to fill the drive is once the drive is full and plugs are installed, the drive is then laid on it's side with the upper vent facing up. The upper plug (vent) is then removed and lube is poured into the vent hole until the upper portion of the drive is full.

The lube bottle needs to be drained, cleaned out and refilled every few years to keep the thickening of deposits filling the hose.

As many can contest to issues with known good mechanics, there are shops with good reputations which have been doing bad jobs for a long time, to only later find out that those shops were the issue. Not saying your shop is the blame but what your stating just doesn't happen in 95% of the cases and Bravo 3 drives.

Foam in a lube bottle means water or air has entered the drive. The lube bottle has a one way valve, it lets pressure in, but not out. When the drive cools, air can come in and allow lube to decrease, but heat will expand the lube but valve will seal off. Bottles can go bad, but this is with leaking bottles.

The folks on Off Shore Only that run High output motors for long WOT runs, swear by Amsoil extreme gear lube. I do not think your issue is the lube, not that the Amsoil will not benefit your drive, you just have a maintenance issue IMO
 
My mechanic spoke at length with Merc rep. They conclude that the boat is at the top of the design specs for that drive.
There are 550 hrs. on the drives. Combine these and you have wear and tear on gears. That has produced excessive heat
which wears even more.
So, you are right it is a maintenance issue. Merc suggested replacing the drives. I'm going to rebuild.
 
Info for thought, but as you say the first was OK for 550 hours: The B3 lower is a B3 lower only difference is the ratio and doesn't matter if its a standard, X or XR.

The upper is where things can change and beefed up a bit. Your mechanic could install higher load gears.

Hope after your rebuild you post back and let us know how things are
 
Wow, so I am at 600 hours... and a 34PC.. So I guess I am over spec for Bravo III's :mad:
 
+1 Alldodge. I just went through this a week ago. Long of the short.... had lower units replaced 2-3 yrs ago. This season almost has been a constant top up of G.O. on strbrd drive. Finally put on the hard and pulled drive. Pressure test of drive revealed bad outer carrier seal. Oil pushed out then as it cooled when stopped sucked water back in. Diluted and blackened G.O. Final result? New complete from Merc - 7800. Carrier was also just starting to pit on edge. installed new drive w/ Simreck outdrive shower (no drilling) and measured temp between drives while underway at 3400 rpm. New drive upper case 88deg starboard side (w/ older style shower) 98deg. I use Merc 90 G.O. Ran her in 4 footers on the C.B. Sat 9/2. No problems
 
I did the rebuild at the beginning of August. Drive has run perfectly since.
I plan on doing the other drive over the winter lay up.
 
Try to pm you at no success, I have the same problem with the seaweed and been doing a ton of research on how to install the sea strainers with thru hull fittings.
Can you please take some pictures of the installation in your boat.
Can you please tell me the strainers you use, I am leaning towards Perko 493
I heard you lose 5 to 10 mph putting in the thru hull, Did you notice any difference
Did you cut the hose in the drive so it splashes on the inside of the drive as you drive as per merCruiser

Thanks for all your help
Don Welch
631-433-8602
2008 34' PC
 
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Sparkey600, did you ever move forward with the thru hull cooling? I have the same boat (2008 34PC Bravo3) thinking of this for a winter project. can contact me if you like, Mark 631-433-1283
 
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