40hp, 3cyl, 1992 Yam OB overheats

[halmc]

Yup, it sets the control box alarm at idle, with muffs or in the water; and in the Water with WOT. Here's what I've checked:

1) pulled lower unit, inspected impeller, no apparent defect and it's keyed properly to the shaft.

2) temporarily and briefly disabled heat sensor -- other symptoms of overheating appeared rapidly and persuasively.

3) Removed and inspected thermostat. Thermostat seems to have stuck wide open long ago. While the thermostat was out and with the lower unit off, I applied moderate water to the tube that sticks into the water pump. Water comes cascading out the thermostat hole and the pee hole. Buttoned the thermostat housing back up, ran the engine with water furnished to the tube, alarm never sets, engine never overheats. (at brisk idle) And it pees better than I do.

4) measured compression to check for blown headgasket: all cyls 120psi on the nose, throttle closed.

5) Inspected the waterpump base and all passages associated with the water pump. No abnormalities noted.

When the engine runs, it seems to have its normal power.

I could sure use some fresh ideas . . .

 

[cousinabe]

Re: 40hp, 3cyl, 1992 Yam OB overheats

replace the entire water pump, not just the impeller, but the wearplate, etc. bad impellers look like good ones.
while you're at it, replace the tstats, gaskets and inspect the poppet valve for debris.

 

[halmc]

Re: 40hp, 3cyl, 1992 Yam OB overheats

replace the entire water pump, not just the impeller, but the wearplate, etc. bad impellers look like good ones.
while you're at it, replace the tstats, gaskets and inspect the poppet valve for debris.

What poppet valve?

 

[cousinabe]

Re: 40hp, 3cyl, 1992 Yam OB overheats

oops... i thought the 40hp had poppet valves, but they don't.

 

[halmc]

Re: 40hp, 3cyl, 1992 Yam OB overheats

oops... i thought the 40hp had poppet valves, but they don't.

Fair enough. Here's the impeller. It fits very tightly into its little housing. Hard for me to believe that is worn bad enough to make a difference, harder still to belive that the wearplate is the issue since it has no discernable wear whatever.

HELP!!

 

[cousinabe]

Re: 40hp, 3cyl, 1992 Yam OB overheats

That thing is SHOT! get yourself a new kit.

http://www.boats.net/parts/detail/yamaha/Y-6H4-W0078-01-00.html

This may help too.
http://www.thehulltruth.com/shipyar...124425-how-yamaha-f200-water-pump-change.html