I have twin bravo 3's on my sundancer 310. My starboard side is overflowing the reservoir when under way. I opened the hatch after a 5 mile run and it was up to the cap. When it cools off it drops to the full level, or a smidge below it.

Since, i installed a new cap. Same problem.

Not sure what else i can do while the boat is in the water short of shot gunning a new reservoir just in case the sealing surface is not sealing.

Other than that, i'd have to pull boat and drop the fluid and do a pressure check, see if the res or cap is leaking.

Could be over heating due to some internal reason i suppose. But i thought i read somewhere that even overheated oil should not expand past the cap.

Any other ideas?

Does your cap have a rubber seal? And does it have the vent thingy on it.
when you can check your bellows for oil I’ve heard of leaks on driveshaft causing stuff like this.

im putting a drive shower on my b3 to prevent heating issues like you’re experiencing. But I just got notices that my bearings I ordered in February shipped last week. Good luck man.

im guessing you’re needing internal seals, a new/bigger reservoir, and probably a cap, a drive shower probably wouldn’t hurt anything to help keep temps under control.

the most common problem are those valves on the cap. The b3 makes some serious heat, that causes the lube to expand.

Since you already changed the cap, I'd say the lube is getting too hot or you have an air pocket in the lube inside the drive. Not likely an air pocket though if you have at least 5-10hrs since a gear lube change.
I'd get IR temp gun and compare temps of the gear lube in each reservoir and also after running for bit, maybe jump in the water and just feel the drives and see if starboard one feels hotter.

ir temp gun on reservoirs doesn’t work. Been there done that. There isn’t enough of an exchange with drive to see an appreciable difference in temp. We were turning drive oil black and saw no temp difference.

could add drive showers to see if that helps. Other thing is to check gear oil color. Idk what your running but if one is darker than the other or smells burnt…your cooking the oil. Could be bad gears or bearings.

With replacing the cap didn't work, I'm leaning toward water getting in

Spin the props on both drives, listen and feel if there are differences

I water was getting in, I would assume the oil level would not go down to the normal level on the res. I'd assume it would stay high.........

I have about 3.5-4 hrs on it this summer only.

I have the Simrek drive showers installed on each drive

drives are normally pressurized. I’d think oil would get pushed out before water would come in…

easiest check would be pull drain plug. If it’s milky then water is getting in.

Update on this:

First off, as previously stated, i installed a new cap. That did not fix the issue.

I ordered and installed a new Quick Silver reservoir and cap assembly. The new bottle has molded in range marks for normal operation. I filled to the bottom range mark. Went and tested, and the oil only came up about half way to the top mark on the bottle. No where near the issue i was having prior. So i'm guessing the old resi had a leak, or the cap wasn't sealing on the old resi.

Either way, new bottle/cap assembly fixed it.