'91 Yamaha 130hp overheat problem

[91Whaler]

Long story. Bought rebuilt lower unit this winter (old one was cracked and had water in oil). Ended up rebuilding the entire water pump before installing lower unit. Problem is: strong stream from telltale at idle and up to 5000 rpm with engine in neutral. But, underway, at 4000 rpm or higher (boat is a 19' Whaler) going about 27 mph, the telltale stream gets weak and eventually the engine overheats. Never had this problem with my old lower unit. Seems like the water pump is starved for water on the intake side at higher rpm/boat speeds resulting in lower pressure/flow. Thoughts? Suggestions?

 

[rodbolt]

Re: '91 Yamaha 130hp overheat problem

are you sure you have a pre 95 gear case? the cups changed in 1995 and while the pre and post stuff will interchange somewhat if your not careful you will have issues.

 

[91Whaler]

Re: '91 Yamaha 130hp overheat problem

I'm not positive about the year of the lower unit. It came to me with an arrangement that my local dealer couldn't find in his parts book: a system of spring washers, a plastic grommet and a metal cap that went over the impeller and under the cover. He couldn't find the cup to fit over that arrangement and recommended I replace the cover with a new one, use the cup in the water pump rebuild kit with the impeller supplied and eliminate the washers, spring washers, grommet and metal cap. So I did. Is that the problem? Why? And why couldn't he find the arrangement I have in his parts book? (I brought the aftermarket book I have showing the arrangement, but that didn't help.)

 

[91Whaler]

Re: '91 Yamaha 130hp overheat problem

Update. I think I may be getting closer... This lower unit appears to be a later one. I changed the water pump arrangement to an earlier one (insert cartridge, housing, omitted wave washer, spacer, collar). Could that be the culprit? How do I tell what year my lower unit is? (The part numbers for the cartridge and the housing are different for '95 and '97.) It is a 25" shaft length; that appears only to have been supplied in '95. From '96 and '97 it's not listed, so I guess it's a '95...

 

[91Whaler]

Re: '91 Yamaha 130hp overheat problem

Anybody out there? Am I doing something wrong?

 

[pine island fred]

Re: '91 Yamaha 130hp overheat problem

Seen this happen before. You will have to drop the leg and look down the pump outlet. See if it is clear or did the stainless steel cup become unindexed when you put it over the impeller. Cup can turn and partually block the outlet. You are not burning much fuel at 5,000 RPM in neutral but a whole lot at 2500 under load making much more heat. might work. FRED