98 120hp water pressure questions

[RadioWaves]

The water pressure indicator on my 120hp Force reads 2 to 4 PSI while underway and to 1 or so PSI at idle after startup. <br /><br />After it warms up, the PSI drops to zero at idle but I still have water spitting out of the exhaust pretty good and a small dribble coming out of the pee hole. Never has the overheat buzzer gone off.<br /><br />I see a lot of discussion on Force water pumps and low flow at idle; what gives? Should I change out the water pump? I don't think it's ever been replaced.

 

[roscoe]

Re: 98 120hp water pressure questions

Yes , change it. Change the entire water pump.<br />Even one overheat incident can be deadly for your Force engine. Change the impeller every year on your Force, cheap preventive maintenance.<br /><br />My water pressure guage reads 2-3# at idle,<br />8-10# at 2500 rpm, <br />and 12-14# at WOT.

 

[RadioWaves]

Re: 98 120hp water pressure questions

roscoe, THANKS! The next trip is from the marina to the boat ramp and trailer for water pump replacement.

 

[RadioWaves]

Re: 98 120hp water pressure questions

Here's an update. I don't know what good I've done but I'm not there yet and I'm stuck.<br /><br />I dropped the lower unit and replaced the water pump assembly. That's not just the impeller, it was a whole pump replacement. I also changed the water pressure gauge as it had given up the ghost.<br /><br />Now... I run the RPMs up slowly to 4200 and the water pressure increases to about 8-9 PSI at 4200. If I stay there all is well. If I go up to 4900 (WOT), the water pressure drops down to 2 to 3 PSI and stays there until I drop back to idle. I can then go back to 4200 and return to 8-9 PSI.<br /><br />Per the manual, I checked the overtemp alarm and it functions normally. It has never gone off while the engine is running.<br /><br /> Any ideas folks? I'm lost...

 

[RadioWaves]

Re: 98 120hp water pressure questions

Same boat a year later with the same problem. <br /><br />I've installed a new water pressure indicator and the readings are a bit more stable. But the pressure stills falls off at wide open throttle. The overheat alarm has never gone off and the engine is cool to the touch right after shutdown. I don't believe the motor is overheating but I sure would like to get this indication issue resolved so I can quit worrying about it!!!<br />

 

[roscoe]

Re: 98 120hp water pressure questions

Perhaps your motor is mounted too high on the transom. This would allow the water intakes to be out of the water as the speed increases and the boat is lifted up out of the water.<br /><br />Where is the cavitation plate, in relation to the bottom of the hull?<br /><br /> http://www.iboats.com/ref/images/shaft_length_small.gif <br /><br /> http://www.iboats.com/ref/shaft_length.html

 

[RadioWaves]

Re: 98 120hp water pressure questions

The cavitation plate is submerged about 5 inches when sitting still. The prop never cavitates when turning hard so I think it would be submerged enough during operation. <br /><br />It is a pontoon boat and it has the engine mount plate way down low next to the water.

 

[roscoe]

Re: 98 120hp water pressure questions

Hmmmm, I dunno. <br /><br />I guess you could try backflushing the cooling system, to see if there is any foriegn material causing a blockage. Remove lower unit and thermostat, then use a garden hose to force water up the water tube. Then force water into the thermostat housing.<br />?

 

[RadioWaves]

Re: 98 120hp water pressure questions

The boat came out of the MS river where it was docked at Greenville, MS. When I moved it to the lake, the lower unit was encrusted in "river crud". <br /><br />Since it's been in this beautiful Arkansas lake almost a year, the lower unit is clean and you can actually see the stainless steel prop. ;-) All the river crud is gone from the outside.<br /><br />When I changed the impeller and pump last summer, the internals looked clean in the lower unit. However, you may have a point as it was amazingly crud covered when I first put it in the lake.<br /><br />Sometime in the next few weeks I'll pull it out to perform the "flush out" maneuver and reassemble.<br /><br />Do I need a new gasket when pulling the thermostat or do you think I can reuse the existing gasket? <br /><br />I'll let you know how it goes.<br /><br />Thanks for all the input roscoe

 

[roscoe]

Re: 98 120hp water pressure questions

Gasket may be good to re-use, depends.?<br /><br />Might be able to get a new gasket, or a thermo and gasket from NAPA store.<br /><br />Good luck.