New 2020 Mercury 225 Pro XS 4S, no to little water pressure?

[rdcarleton]

1. Engine Serial Number: 2B742873
2. Year/Make/Model: 2020/Mercury Pro XS 4S
3. Prop you are Running: 24 Fury
4. Current Maximum RPM: Still in breakin
5. Idle and WOT Water Pressure Readings: 0 at idle, maybe 8 psi at 5000
6. Smartcraft or Analog Instruments? Analog

I bought a new Phoenix 919 Pro XP, with this engine last week. Put boat in water for the first time Saturday morning. noticed imediately, my water pressure (analog) was no to low. Up to about 2500 rpms it shows basically 0 psi. at 3500 rpms it starts to crack 4-5 psi. it stays on 5 psi through 4500 rpms, I do have smartcraft but water pressure was not enabled. It's possible that its not enabled because I don't have a digital sensor (I'm not sure on this)...so this water pressure reading is from the phoenix analog gauge. I noticed on the smartcraft, engine temp was holding at 140 within a degree or two, but I know outpboards live and die based on water pressure so I took no chances and loaded it up to the dealer. dealer had boat for about 4 hours and said the original pre-delivery of the motor showed 20 psi. after dealer inspected pressure on the hose, they observed the same pressure I did. They blew air through the lines and checked the gauge. They said every thing checked out. They also took the boat to the water and ran it with diagnostics. Mechanic said he was able to get a reading of 10 psi at WOT and that according to Mercury this was within spec (8-30 psi at WOT). They said they also observed no overheating during this time. They put everything back together and said the motor was OK to run. I took it back to the lake and put the first two hours of breakin on it. During this time I watched engine temp like a hawk and it never went over 140-142. During this time water pressure was never more than 5 psi. At the two hour mark, I started making a few higher rpm runs (5000-5500) and I saw water pressure get very close to 8-9 psi.

? Is this pointing to a water pressure gauge or sending unit problem? or is the Mechanic correct in that "some of these motors are just like that?" Mechanic said, he had another customer with the similar issue and he has been running his for a year now with no issues.

?If its a gauge or sending unit, will a digital sensor and smartcraft give me a correct reading or is it going to show basically the same thing that the analog gauge is showing?

?Is 8-30 psi at WOT, really the mercury spec per the Mechanic (dealer)?

thanks for any advise.

[5keepers2]

I have buddy with new 200 4/stroke. The pee stream is good and strong. The analog gauge works almost same as yours. We put in a tee and also installed water pressure sensor for digital reading on smart craft. The pressures were much higher and I believe correct from the digital reading.
I have 150 4/stroke and also have both analog and digital water pressures. My pressures track almost the same.
I am thinking your analog gauge is slow response and possible low reading. It may get more responsive with time! Lets hope so!

[EuropeanAM]

You will need a digital sensor to read Water Pressure on Smartcraft. STRONGLY recommend you look at the post in the FAQ Section that shows an ALTERNATE method for you to have BOTH Analog AND Digital. The parts ARE DIFFERENT- so use the part numbers shown in that post if you want both to work.

You will need to have 15+ at WOT for your setup. Prefer to see 18 or higher.

Not uncommon to see right at 1 psi at idle... which is fine. No way you can see that on an analog gauge (accurately).

[99intimidator]

So there is more engines having this problem I have smartcraft gauges on mine I only see .4 on the water and ran it in 100 gal water tank still same reading. When I had it in the tank I hooked the coastal flush hose with the engine off and key on the reading was the same on the gauge. Mercury service rep said mine is ok as long it doesn't have any over heat warnings.

[DaveTTN]

What is your prop to pad measurement? Mine is around 2.5” and I see 1 or 2 at idle and 25-30 psi at WOT. I wonder why they didn’t put a new impeller in it?

[99intimidator]

I think its on the newer motors that are having the problem. The only things that I see different is they added holes to the lower unit and a different exhaust water strainer. I haven't ran it since I got it back from the shop. Should be hitting 10hrs tomorrow going to run it hard and just watch oil and water temps.

[mjw930]

What is your prop to pad measurement? Mine is around 2.5” and I see 1 or 2 at idle and 25-30 psi at WOT. I wonder why they didn’t put a new impeller in it?

2.5” to the prop? Do you mean the cav plate is 2.5” above the pad? If the prop shaft is only 2.5” below the pad you’re fully surfacing the prop and that ain’t gonna happen without a Sportmaster lower. How much setback? Saying 2.5” to the prop means the prop shaft height to anyone who sets up motors.

Is yours a TM II lower or the standard bullet? 2.5” below the cav plate is a bit deep for the TM II, they like closer to 4” with the right props.

[DaveTTN]

There are many threads on here about how to measure prop to pad. Basically it's how far the centerline of the prop shaft is below the pad of the boat, it has nothing to do with the cavitation plate. The only thing you use the cavitation plate for is to put a level on to make sure your engine is trimmed level when you take the measurement. I have the new TM II lower.

[mjw930]

My apologies, I’ve been setting up high performance boats for decades and have always used the prop shaft measurement because our drives are surfacing (Speedmaster and Sportmaster lower units). On virtually all “fishing” boat forums and mechanics that service this market they use the cav plate measurement because they all run submerged drives. Their goal is to get the plate running at or near the surface.

Since the TM is semi surfacing it splits the difference. Mercury wants you to have water at the wingplate which is 5” above the prop shaft and is a necessity if you have the 5 hole version. If you have the 3 hole version you can get away with 4”.

Opinions vary but I’ve always used 1.5” of water rise per 12” of setback so if you are running 2.5” below you would have either 12” of setback for a 3 hole version or 20” of setback for a 5 hole.

I’m running 24” of setback and 2” below the pad and I’m starved for water in turns with the 5 hole version. I have 2 options, index the 10” Atlas jackplate down 1.5”, which is what Key West recommends or plug the top 2 holes. I’m going to plug the top 2 holes first and see how it works but I suspect I’ll need to index the plate.

[ifishinxs]

Analog gauge is fed by a tube from the motor to the gauge. This may sound elementary but did anyone check the tube for a kink or debris in the line. My last boat had the tube zip tied together with some under dash wiring. Fixed the kink and gauge worked like a champ.

[EuropeanAM]

You SHOULD (with a Digital Sensor and a Smartcraft Instrument) be seeing 1-3 psi at idle speed.

And on a bassboat- you should have no problem maintaining 18+ at WOT.

Anything in between those is just that- "something in between".