Tohatsu 3.5 - Oil won't flow into lower unit

[WWPotterOtter]

This is a 1999 3.5 HP longshaft with Forward/Neutral. I'm changing the lower unit gear oil using a pump that screws onto the neck of a standard gear oil container. The filler tube ends in a fitting that screws into the lower drain hole. The pump works, all fittings and tube are clear. The upper vent is properly left open.

The old oil seemed to drain out okay, but it looked like less than usual came out. It seems like there's a clog in the lower unit preventing the oil from going in. Pumping just causes back pressure. I also tried pumping into the upper vent hole: same clog. What could this be? How to fix?

The motor ran fine just prior when I was flushing it in a tank for 15 minutes. The gears still shift easily, and the prop turns when starter cord is pulled.

Could the impeller have suddenly failed and is now causing the clog? Just discovered my regular outboard guy has gone out of business.

Thanks!

 

[pvanv]

Re: Tohatsu 3.5 - Oil won't flow into lower unit

I assume your model is M3.5B, since you have neutral capability. In Tohatsu/Nissan land, always specify the precise Model (from the transom clamp assembly), not model year.

No, the impeller would not cause your issue. It's in a separate housing on the driveshaft, on the top of the LU, and has nothing to do with the gear oil.

If it were in our shop, we would pull the prop housing (two bolts with 10 mm heads) and investigate. You likely have a piece of debris in one of the lube holes.

 

[WWPotterOtter]

Re: Tohatsu 3.5 - Oil won't flow into lower unit

Thanks for your help, Paul. It is indeed a 3.5B long shaft.

I took it in to a shop and they found that a seal associated with the water pump had dislodged...plus there was some corrosion...and the combination was creating an obstruction. They are going to replace the water pump. I think, though, the propeller shaft seal should be replaced, too, given the corrosion. They said the gear oil looked milky. Frankly, I didn't see that when I drained the oil...but I have no experience.

Eliott

 

[pvanv]

Re: Tohatsu 3.5 - Oil won't flow into lower unit

If it was in our shop, I would recommend driveshaft and propshaft seals and shift shaft o-rings as well. The parts are relatively inexpensive. If there was a dislodged driveshaft seal (at the water pump), there was likely some (milky) water in the LU lube.