Drive lube overheating - 7.4mpi/bravo 3

Hi Guys,

This is my 2nd attempt at fixing the problem. The package is a 99 Mercruiser 7.4MPI and a Bravo III outdrive. On a 23ft searay cuddy.

Late last summer I started getting a burning smell from the engine compartment when I was running at higher RPMs (cruising at 3200revs was OK, any higher it started to smell). Some things we noticed:

1. The drive fluid pressurized and blew out the top of the monitor cap. This happened twice. Changed the drive fluid, no water, it looked fine.

2. Noticed steam coming from the engine compartment. Turned out to be the manifolds. Replaced those, no steam. Still get the burning smell back there.

3. Thought maybe the flappers had become lodged in the exhaust. Pulled the leg this winter and it's all clear.

So, as I thought back to the summer, I hit a log a couple weeks before the problem appeared. No visible damage to the outdrive, but it did get a pretty good thump.

I'm about to have someone open up the drive and inspect it. Any other ideas as to what could be causing the problem before I start throwing money at the mechanic?

thanks,

Scott

Re: Drive lube overheating - 7.4mpi/bravo 3

Ayuh,....Why you tearing the drive down, when the motor appears to be overheating..??

Did you change the Impeller yet,..??

Re: Drive lube overheating - 7.4mpi/bravo 3

You keep saying the gear lube looked ok, no water. But what was the condition of the gear lube. Black and burned smelling? Any metal on the magnets?

The reservoirs are not vented for pressure, the cap is set to suck air in as the level goes down, but it will pressureize when the gear lube is hot. And it shouldn't be getting that hot. But the gear lube should not be getting that hot.

Do you make very long trips when running? What is the water temp where you boat?

Re: Drive lube overheating - 7.4mpi/bravo 3

Thanks for the replies guys.

Bond-o: I'm pretty sure the motor isn't overheating. It has closed cooling on the motor, the gauge comes up to temperature and stays in the 165-170 range on plane (I guess the gauge could be shot) and the motor and manifolds are not noticeably heating up. I could point a temperature gun at it to make sure.

Don: The lube had about 30hrs on it when I changed it. It was darker than when it went in but not black yet, and didn't smell burnt. There was no metal on the magnets either. All looked OK at the time.

I'm boating up in Vancouver (BC) so the water temp is usually in the high 60s, although last year it got warmer. My trips are usually 30mins or less at a time.

scott

Re: Drive lube overheating - 7.4mpi/bravo 3

Also, yes the impeller was new last season. You'll notice the post where it took me 2 tries to get it right

Re: Drive lube overheating - 7.4mpi/bravo 3

Was any drive work done to the drive prior to this problem?

Re: Drive lube overheating - 7.4mpi/bravo 3

Nope, hadn't been removed or worked on at all from the time it was running fine until the problems surfaced.

unless you call running into a log, being worked on

Re: Drive lube overheating - 7.4mpi/bravo 3

unless you call running into a log, being worked on

Click to expand...

No, wasn't counting that, but hadn't forgot about it either.

If the boat is out of the water, grab the aft prop and push it in and pull it out and let me know how much end play you have.
None, barely feel any, very little, 1/32, 1/16, something like that. No need for super accurate at this point.

Re: Drive lube overheating - 7.4mpi/bravo 3

yeah, its out of the water still. there's a little play, not much. I'd call it 1/16 at most.

Re: Drive lube overheating - 7.4mpi/bravo 3

Ayuh,... I'm sure Don has a line of thought going with his question,..

I just don't see the Drive overheating with the symptoms you describe...
Other than the oil bottle thing,...

Heat,+ Smell from the motorbox, would lead me to the motor...
You also state you pulled the drive, lookin' for the shutters,...
What about when the manifolds were swapped,..?? The shutters were right under your nose,...
Were they in good shape,..??
They still could be an Issue, that didn't fall all the way to the drive...

Re: Drive lube overheating - 7.4mpi/bravo 3

About the only time I see gear lube getting pushed out of the bottle is when the seal is missing from the cap. Might check the cap.
Good Luck Muc

Re: Drive lube overheating - 7.4mpi/bravo 3

If the cap on the reservoir is ok and it was just building up that much pressure, it may very well be the drive. I had one B3 the guy said he had to fill his reservoir several times, when we checked, there was no end play, and actually a lot of preload on the inner propshaft. This was a brand new replacement drive that was only on the boat for a few weeks, Merc replaced it. But your drive seems to have a LOT of excess end play. You should be seeing .001 to .012 inches of end play. That is a LOT less than what you are feeling, so it might be time to have it looked at.
Probably a lot cheaper to fix it now, that to wait till it fails completely.

Re: Drive lube overheating - 7.4mpi/bravo 3

thanks guys.

Bond-o: when i had the manifolds replaced the mechanic who did it noticed the flappers were missing and they weren't visible. That's why I thought they may have been stuck further down stream causing my problem. I was going down the motor overheating path as well but the fact that my drive lube blew up twice and that the motor doesn't seem to be running hot led me to the drive. I will do a little more checking on the motor side to make sure.

I did check the lube monitor after it overflowed (thanks to some threads on the forums) and the seal is in place.

Don: Thanks for the info on the prop shaft play.

Think I'm going to try and completely eliminate the motor overheating as a cause this weekend, then have the drive looked at.

I'll come back with whatever I find

Scott

Re: Drive lube overheating - 7.4mpi/bravo 3

I'll come back with whatever I find

Click to expand...

Ayuh,... You've got an Interesting issue,... We'll be waitin',... Good Luck...