High Pressure in Gear Lube Reservoir

[MLauman]

A buddy of mine has a Bravo 3 that is building up high pressure in the gear lube reservoir. It is so bad that at one point it ruptured the barb on the reservoir and spew lube in the bilge. He replaced the reservoir with a new one, but still has the pressure problem.

The reservoir was properly filled when it was replaced. He ran the boat this past weekend. Then yesterday he noticed that the reservoir was full - not to the full mark, but to the top of the bottle. He slowly unscrewed the cap and you could hear the pressure releasing. The boat had not been run in several days.

I realize that one source of this type of problem would be a hot outdrive. But I assume that after it cools down the pressure would go down as well. Kind of like a car radiator - maybe a poor analogy. And I'm not sure why his outdrive would be experiencing abnormally high operating temps.

Any ideas?

 

[Lazy Daze]

Start by draining a bit of gear lube out of the lower drain hole on the drive. Just enough to see the color/consistency of it to make sure water is not getting in.

 

[Stray Cat]

In addition to L.D. above, has he tried running the boat with the res cap 1/4 to 1/2 turn from tight? That res cap should be vented. If his drive is running that hot, you should see a bunch of steam come from the drive when he comes off plane....what year and model is his boat?

 

[Henry Boyd]

Oil wouldn't expand that much no matter how hot it got. The radiator example does not apply because a radiator contains liquid and steam. As the steam is created it has greater volume and pushes anti-freeze into the expansion tank.

The gear oil is not transitioning into a gas vapor, it would only burn at high temps, so something else is creating pressure. It is more likely as LD suggests water being introduced into the case. In theory if the water got hot enough in the drive, it could turn to steam and cause a pressure bubble, but that seems like a real stretch.

Henry

 

[Lazy Daze]

I was thinking more along the lines of the water intrusion causing the air in the lines/lube tank to compress. Correct me if I'm wrong, but doesn't that little orange nub/vent on the tank cap vent inwards? In other words, to relieve possible vacuum build-up? I know when I'm changing gear oil, I use my compressor to blow the oil out (just a few psi) and I seal the blow gun tip (rubber) right on that vent.

Although, I didn't even think of that steam aspect, Henry.

 

[jwfoster4]

The exact same thing happened to me. When my bottle blew, I replaced it and hesitantly went back out on the water. It did not take long. The bottle swelled up, but I shut down before it blew. The pressure also caused oil to be forced past my prop shaft oil seal. I saw drips coming up about every 5 seconds. Ended up being a missing thrust washer left off by the previous owner/mechanic. No telling how long it was run that way. I assume it allowed water in around the prop shaft. Several gears were very worn. I decided it wasn't worth it to rebuild it, so I replaced it. Wish I had better news, but you have outdrive repairs in your future. Anyone want the old Bravo III Outdrive?

 

[MLauman]

Boat is a 2000 270DA w/ 7.4 Bravo 3. He's planning to pull it next week to check/change the fluid and get a pressure check on the drive.

jwfoster4 - Did you ever do a pressure test on yours while it was bad?

 

[Stray Cat]

With that year, it could be the older generation of Bravo 3. I lost enough aluminum material around my shaft seal from corrosion, that had I not caught it, it would've allowed water in the gear case. Monofiliment fish line will also tear a shaft seal out if it get balled up enough on the front prop....

 

[jwfoster4]

No, I never did a pressure test. No need. I knew it was a goner.

 

[robingb]

hello mlauman, i seem to be having same problem with my bravo 3. it is near new however it had to be reinstalled recently to replace yoke and other stuff. i would be interested in knowing what your problem ended up being. thanks, gary