yamaha's overheating

[captnbob]

Have twim 1990 yammis in for service and impellars replaced on both engines. Now they overheat on the hose . Did not before service. Do not overheat when backed into the water. suspect air leak in lower unit. Took apart one of the pumps and did not see bushings in the top half of housing where shaft comes through. Could this be the problem? Has to be something the mechanics did since I didn't have a heat problem before service. They did replace thermostats. No water is getting up to the block but is coming out tell tale. Can take out thermostats and should have water coming out when running right??

 

[12Footer]

Re: yamaha's overheating

I can't comment on the bushing question, as I have never changed-out a yammy that had one.<br />But theoreticly, it could just be that the new impellers are pumping more water than they can draw from your water source.<br /> If you can back it into the water, and have no problem,and run as cool or cooler than before, I would highly suspect that.<br />Do not operate your engines without a tstat in place, except to test your theory. Running without tstat can warp heads and exaust port/manifolds.

 

[captnbob]

Re: yamaha's overheating

We just pulled the tstat to see if water was getting into the block and since no water came out it appears the block isn't getting water at all. Does it seem resonable to think that even if water supply was not quite enough, shouldn't there be some water coming through the block? Never did this prior to putting in new impellars. One engine wouldn't even prime so we put in a new housing and after that as soon as we cranked the engine we had water coming out of the tell tale......but no water in the block. Block has been pulled and there are no obstructions. Any more idea or thoughts?? Thanks for your reply.

 

[lakensea]

Re: yamaha's overheating

What type of motor flusher are you using? With the big Yamaha you must use a dual feed type. The Yamaha has a divider plate between the water inlet screens.

 

[captnbob]

Re: yamaha's overheating

we are useing the dual feed type. But before the impellars were changed we used the side feed type with no problems. Never overheated.<br />txs

 

[rbu]

Re: yamaha's overheating

I sort of had a similar problem on a 1988 225 Yamaha. After I changed the water pump, the engine started overheating. Did you check the bypass valve? I think it is called a 'popet' valve. This is usually the culprit. I changed mine and problem was solved. It is just a plastic valve. Sometimes it gets stuck in a seated position during winter layups or it gets clogged and needs to be cleaned, checked, replaced or whatever. That is what I would check next if I were you.