2003 DF 140 Water pressure issue

[kirt123]

I have an 03 DF 140, About 200 hrs on it. I just replaced the water pump for the second time about 10 hrs ago. After this I noticed that the water pressure at full throttle is a little lower than usual (or I think, I believe it used to be 11-12 psi and now is 8-9 psi)and when you come off plane it goes down to nothing for a bit, after coming off plane if you rev the engine in neutral it will start to pick back up after about 10-15 secs and return to normal at idle. On the way to full throttle the water pressure peaks at about 4000 rpm at almost 15 psi. Then drops back down to a bit under 10 while running at 6200 rpm. Like I said I dont remember having this happen before, I took it out and adjusted my manual jackplate down a bit after I discovered it was running at about 7.5 psi and it raised it about 1 -1.5 psi at WOT. My question is could this have anything to to with the pressure relief valve? I also saw somewhere that these motors come with a plug for the exhaust port that is by the pisser. I dont remember it ever having one but I know it does not have one at the moment. Any tips would be appreciated. Adjusting the motor down further would not be the answer, as the AV plate is barely above the water now and any further and it will start porpoising. What is the normal PSI at WOT for these motors. By the way I have not experienced an overheat per the buzzer but I am being cautious as I dont want to have to deal with the consequences if it does overheat.

 

[kirt123]

Re: 2003 DF 140 Water pressure issue

Ttt

 

[99yam40]

Re: 2003 DF 140 Water pressure issue

Did you replace just the impeller or did you put in a kit with plate and cup?
I would drop the lower unit and look to see if something is wrong with the way the installation went like cup misalignment, especially if it had better pressure before the change.

not sure what you mean lowering motor will cause the boat to start porpoising, usually that is caused by the trim being up a little too high, at least all the boats I have run did.
Checking the PRV would not be a bad idea,but you need to make sure you are not sucking air into the pump if the installation has no problems.

 

[kirt123]

Re: 2003 DF 140 Water pressure issue

Thanks for the ideas, I only replaced the impeller, I will pull it and look at the gasket. Also if you lower a motor too much, the AV plate goes below the water at speed, this results in water flowing over it in turn causing the boat to porpoise as it affects lift. I am not totally sure on what the pressure was before but it seemed higher. The thing that puzzles me is that once you stop, it takes a bit for the pressure to build back up. This is why I thought it could possibly be the valve malfunctioning.

 

[Silvertip]

Re: 2003 DF 140 Water pressure issue

What you may be seeing is normal cycling of the thermostat and pressure relief/bypass valve. At idle the thermostat will close to keep engine temp up and it will open as that temp rises. The pressure relief/bypass valve will be closed. At speed both the thermostat and valve enter the picture so cycling of those will affect water pressure. You may want to disconnect the hose at pressure gauge and with a bucket handy, allow some water to pass through the tube to flush out and debris that might be in there. Then blow out the water and connect the tube. Water does not flow through that tube in operation. Water "pressure" compresses the air in the tube which makes the gauge work.