1986 Yamaha 115 lose of water pressure

[Pete Singleton]

I have a set of twin '86 Yamaha 115 hps. End of 2002 season on run in from offshore temp buzzer went off on starboard engine - slowed to low speed engine cooled and ran in about 3 miles no apparent heating issue. Had problem with lower unit same engine and replaced over winter with rebuilt lower unit complete.<br />First run out in 2003 engine overheated. Took to local dealer and was told I had blockage and needed to pull the power head. I elected to have the unit looked at by another repair shop. Said all I needed was new impeller (was supposed to be done with winterizing in '02) and needed new popet valve (plastic valve on block) Completed repairs including new thermostats. First run out - engine overheated. After much frustration the problem seems to baffle all of my local talent. The engine get solid water pressure until I break 3000 rpm, as soon as I go over 3000 rpm, the water pressure gauge drops to zero and the engine overheats (looks like water stream is poor when this occures). As soon as I back off the throttle and the boat comes off plane, the water pressure gauge shows normal and when I hit the throttles, the water pressure builds back up as it should until I again hit 3000 rpm. I can run the engine all day at 2900 rpm with no problem with normal temperature and water pressure. It seems to be the magic 3000 rpm range when the issue begins. Had same service work done to port engine and no problem with it.<br />Also now overheats while on the hill doing flushout. Never did this before problems <br /><br />Any comments appreciated.

 

[rodbolt]

Re: 1986 Yamaha 115 lose of water pressure

hello<br /> well double check the impeller. we had some problems with the rubber becoming unbonded from the hub on a few. if your hub is white plastic toss it in the trash.. check the water strainer screen for damage. also double check the poppet valve grommet. Its rare to see the actual valve fail but I replace a lot of the gromets. the corrosion builds underneath them and distorts them. if your water tell tale is weak on the flusher then try to take the poppet housing off and hold the valve closed manually and see if it helps. also check the thermostats to make sure they are sealed and working correctly.<br /> good luck and keep posting<br /> ans PS are you positive its an overheat and not an oil alarm ?

 

[JohnMadisonCT]

Re: 1986 Yamaha 115 lose of water pressure

I agree, check the poppit valve. My engine overheated as a result of the poppit valve.<br /><br />The problem usually lies with the grommet. Take it out, get a new one. Before replacing, clean the area where the grommet sits perfectly. Alot of salt crud gets on there and as Rodbolt says, it distorts the grommet and the plastic plunger either can't go in, or get's stuck.<br /><br />John