Bravo 3 overheating Outdrive

[Will Fish]

A friends boat is powered by 260hp yanmar diesel which has a bravo 3x drive duoprop. When the motor was installed the raw water pick up on the drive was blanked off as the heat exchanger manifold etc is cooled via thru hull water pick up. He never had a problem for 2 years then started to get overheating in the drive. His gear oil in the reservoir is bubling up and spilling into the bildge after running after 30-45min at cruise. We put a shower on the drive which seamed to help but still happens after 45-60min. My thinking is the water jacket in the drive is clogged which is why the problem did not occur for first 2 years when it was new. I know the impeller is on the motor and since that was blanked off there is. Itching to suck water up from the drive, but thinking the design of the drive with the fins naturally forced water up thru the drive to cool.

Not sure the solution. I'm thinking need to split drive and clean. Also should the blank off plate be removed and the pick up be connected back to the motor with a T? Basically having 2 water sources thru hull and from the leg?

 

[alldodge]

I don't think its the drive, I think its the vent cap on the drive lube bottle. The cap is a one way vent but it does not let air out, it only lets air in. When the lube heats up by the drive it expands, and the cap is designed to keep the pressure in the drive. What is probably happening is the valve is allowing air to escape and therefore the lube oil is also coming out.

Get another lube bottle or just the cap and give it a try.

 

[tpenfield]

I also think it has to do with the gear oil in the drive and/or the reservoir bottle. I would check the oil level of the outdrive, re-fill as needed ad per the procedure outlined in the manual.

The water standard water pick-up typically does not give enough cooling to the outdrive . . . the oil need to be full in order for it all to cool properly.

 

[Fun Times]

When you blocked off the inlet water supply inside the boat/transom assembly, did you cut the inlet water hose on the outside which runs right along the portside U-joint bellows behind the bell-housing?

The hose needs to be cut to so the water doesn't deadhead against the inlet fitting block off cover in turn allowing the water to flow through the dive helping to cool the drive while underway.

Hopefully it's just either a uncut water hose or a failed reservoir cap as mentioned above.

Merc part number 36-806727 1 = Reservoir Cap.

Alpha or Bravo Models Using Alternative Water Pickups
A water inlet block-off kit must be used if the sterndrive unit water pickup will not be used to supply water to the engine. When installing the block-off plate, it is necessary to cut the water hose that is located between the bell housing and the gimbal housing. This allows water to continue to circulate through the sterndrive unit for cooling.
NOTE: Move the trim limit switch wires and speedometer hose to avoid damaging them when cutting the water hose. The existing tie strap and clip can be reused if they are moved and repositioned after the hose is cut.
5. Cut completely through the water hose 5 in. (127 mm) in front of the aft end of the hose where it is fitted into the bell housing. in the area shown. DO NOT damage the U-joint bellows. Discard loose hose piece.
6. Secure the trim limit switch wires and speedometer hose to the remaining section of water hose using existing tie strap and clip.

^ Start on page 63 for more info, install /gas/86017211.pdf - Boat Fix - Boat Fix - Serving ...

 

[Will Fish]

Gear oil has been replaced as per spec and filled according to merc. Draining the old oil looks good still bluish/green like new, just a bit darker. No metal or and milkyness at all.

The inlet hose on port side is cut allowing water to flow thru. I will order a new cap and check it (won't be for another month, but it's a start). My concern is why is the oil expanding so much? I suspect it's overheating. What could be causing this?

 

[alldodge]

My concern is why is the oil expanding so much? I suspect it's overheating. What could be causing this?

The cap is like a lid on a pressure cooker, in increases the boiling point so to speak. It actually doesn't boil, but the gears are whipping up the lube and it starts to expand. So if the cap keeps pressure in the drive the lube does not expand much.

Also best way to make sure the drive is full, is once it is pumped full, replace plug. Then lay the drive down with the vent hole facing up and pour lube in the hole until its full. Doing this keeps the drive from burping the air down the tube and into the bottle