Yamaha 70 HP Overheating problem

[Melbournite]

Have a 1997 70 HP Yamaha 2 stroke. Having overheating problems. Have replaced impeller, checked thermostat is opening, pulled bottom leg off and had hose stuffed up water intake pipe and water seems to be getting up into cylinder head water jacket. . Have removed cylinder head and exhaust covers and cleaned out all of the salt build up. Now at a loss as what to do next. There seems to be a lot of water coming out of the front of the lower leg unit overflow so am thinking the water intake pipe is not connecting with the water pump housing outlet so water is not getting up into the water jackets. Any suggestions/thoughts?

 

[flyingscott]

Is any water coming out the tell-tale what about the water pick up under the pump in the lower unit. Did you misalign the tube when you assembled it at what temp does the thermostat open

 

[Melbournite]

Thanks Flyingscott for your reply. yes there's water coming out in a reasonably strong stream from the tell-tale and checked thermostat and it was opening at the recommended temperature between 52C (118F) and 60C (140F) . There doesn't seem to be a blockage in the water pick up. There is however a strong flow of water coming out of the crack at the front of the motor where the lower unit joins the top unit and am not sure if this is normal.

 

[muzzey007]

Have twin 200hp V6 Yamahas 2000 models and have run one engine no problems but the other engine after about 10mins running the temperature alarm goes off is this a thermostat problem and I believe they have 2 thermostats? Are the thermostats identical in terms of when they are supposed to open?

 

[99yam40]

Have twin 200hp V6 Yamahas 2000 models and have run one engine no problems but the other engine after about 10mins running the temperature alarm goes off is this a thermostat problem and I believe they have 2 thermostats? Are the thermostats identical in terms of when they are supposed to open?

why are you posting this on someone elses thread on a 70 hp motor?

Please start you own thread with all you info

 

[Melbournite]

Another question regarding my original query on the yamaha 70 HP, does anyone know if the water intake pipe where it meets the water pump housing should have a rubber grommet or similar on it?

 

[robert graham]

Another question regarding my original query on the yamaha 70 HP, does anyone know if the water intake pipe where it meets the water pump housing should have a rubber grommet or similar on it?

Yes, there is(should be) a black rubber grommet for the water pipe to connect the top of water pump.....

 

[Melbournite]

Thanks Robert, I can't see one on mine its just the metal pipe going into the water pump housing. Will go to the local Yamaha dealer and see what they say. Do you know if the water pipe can be removed? I've looked through the workshop manual and online but can't find anything regarding the removal and you can't see the top of the pipe unless you probably start taking apart the powerhead.

 

[robert graham]

The water pipe on my C90 Yamaha has a rubber grommet on top of water pump housing held on with 2 Phillips head screws....I'd say if your motor calls for a grommet and your's doesn't have one then that could be your problem...

 

[Melbournite]

I've now taken the water pump housing off and the 70 HP doesn't have a grommet on top of the housing but underneath the hole where the water tube and the housing meet so it's different to the Yamaha 90. I am going to put a new housing and grommet in as mine looks a bit worn and the grommet underneath is a bit loose. Will then test and see if still getting same problem. Apparently there's also a grommet at the top of the water tube according to the Yamaha dealer but you need to remove the power head to get to it.

 

[Melbournite]

Finally got back to the boat have installed new water pump housing with grommet, tested it with outboard in a water tank and everything seems to be working as it should. Water coming out of the tell tale was strong and was able to hold hand against cylinder head. Big test now is to put boat in the water, hopefully weekend coming, and see how it goes.

 

[robert graham]

Finally got back to the boat have installed new water pump housing with grommet, tested it with outboard in a water tank and everything seems to be working as it should. Water coming out of the tell tale was strong and was able to hold hand against cylinder head. Big test now is to put boat in the water, hopefully weekend coming, and see how it goes.

Please keep us posted with your results, as that's how everyone on here learns as we go....good luck!

 

[Melbournite]

Finally got the boat in the water, good news is the overheating problem seems fixed. Think it was a combination of cleaning out the salt build up in the cylinder head & exhaust and replacing the impeller and a new water pump housing. Bad news is now think I have a fuel problem. Will post it in a new thread.