Question- water pressure -- merc xr6 150hp

[Luke Musto2]

Hello everyone,

Thank you for your help on the last question, I have another,

Being this is only the first year I have ever taken a boat out of storage, Im not very knowledgeable and was wondering if someone with more experience can help me out..



I started using the motor and the sensor/alarm on it went off twice yesterday..

I think it was overheating... and am going to have the impeller changed, but Im still wondering about somethings...



I was running yesterday in 2-3 footers, and I wasnt going very fast, barely on plane with the motor pretty much trimmed all the way down.. At this time I ran probably 3-4 miles, during the whole time the water pressure was never more than 7-10 psi and the alarm sounded twice during the 3-4 mile run. ANyone know what should the psi be when on plane?



After it cooled I ran back to the launch and the pressure was over 10 as when I took a more sheltered route and was able to go faster and the psi was never below 10... Once back to the launch I idled for a few miles up a creek... At this time I trimmed the motor up because if I missed the channel I would quickly end up in 2fow and I didnt want to damage the prop.. Had a nice solid stream of water out of the engine and the alarm nevre went off..





Today I ran 8-10 miles up the lake and never had teh alarm go off I watched the pressure gauge and it stayed above 10 for all the trip, but this is what is confusing me..





There is one point when I am running after I am on plane that as I trim the motor up the PSI drops to 7lbs and stays there... as long as the motor is at that trim (about 1/2 way up ) it will stay there even if I go to wide open throttle..( If I kept the motor trimed there I am pretty sure the alarm would have eventually gone off, but if I continue to trim it to the point where I start to get a little chine walk I can get the psi to 13-15 psi at wide open throttle..



This is really confusing me as to why at that one posiiton the psi drops to 7 and when I continue to trim up it increases..



Any insight you could offer would be greatly appreciated...

Thanks in advance..



Luke

 

[Jeff Nichols]

Luke-

I have the same motor--mine's a '97. I went through the same thing about 2 years ago when I bought mine, it was used. First time we took it out, alarm went off. Ended up to be the impeller. No problems now.



As for water pressure, I've been told by those with more experience than I that 12 psi. is about as low as you want to go on that motor. Pressure will change with motor height. The higher the motor is raised, the lower the water pressure will drop.



Let me ask you, do you have a jackplate? Reason I ask is, many times pressure is monitored as a boat is "dialed in" with repect to motor height via the jackplate, normally at wide open throttle with motor trimmed all the way up. (As you may already know, the objective for most guys with setup is to obtain the best overall performance and handling which is achieved via a balance of top speed, RPMs and water pressure----the key being to find the perfect balance of the three. For this motor, that's going to be somewhere in the neighborhood of high 50s-low 60s mph, 5600-5800 RPM, and no less than 12 psi). When your motor is trimmed all the way up is when you need to be sure that you don't drop below 12 psi.



When trimmed down, more of the motor (and the water pickup) will be in the water, so the pressure will be higher.



Hope this helps. Good luck!!