1994 Mercury Pro Max Water Pressure

Read through lots of water pressure post this morning looking for an answer to my question and really do not see anything that matches up with my question.
Just purchased this Boat and motor, Vision with 150hp Pro Max. Owner said during test ride when I questioned him that water pressure gauge low pressure that it had always read near 0 psig on idle and 10 while running. I do not know rpm due to tachometer not working. This is the same situation I experienced on my first run as owner last weekend. I placed hand under water stream exiting motor and it was pretty darn hot after a 1.5 mile run from my dock. I have never owned a Mercury motor with this type of cooling exit system. I'm used to water flowing out of tattle tell at a high pressure at idle. Looking back and seeing water just flowing out of this hose just has me concerned along with the low pressure at idle speeds. I did read in my repair manual normal pressure at 5500 rpm is 12 psig. I ordered and received new water pump impeller, key and SS insert for inspection and replacement this morning. Also, no temperature gauge on panel. I do have a hand held laser temp. indicator that I can use on heads.
Please give some advise on normal water pressure for this type of motor, especially at idle and experiences with type of motor. Also what type of temperature should heads be running.

Thanks!

As you know 15# is ideal. I have seen motors idle a 0 and wide open only 10 and live fine but you need to see that temp to be sure. Low pressure reading could be gauge inaccuracy or plumbing restriction. This is why I have always had both pressure and temp gauges. Good luck.

Rock

Thanks for reply.
What is normal temperature range and what is Maximum temperature for block?

since tha gear case has been changed, do you know if adapter has been changed to one piece?..
i liked a target of 'bout 160 but think most on here like way cooler!.. 170 and i'd be lookin' and checkin' stuff.. heat horn can go off ruffly 190 ta 210.. they aren't too consistent with "when"..

when changin' tha pump it needs ta be "complete" kit includin' base and ride plate.....

This motor should have t-stats and poppet with a two piece plates, correct?

Agree with Rock though...Need a Temp gauge and water pressure gauge. One without the other leads to some guess work. imo
The infrared is good to a fault.

James

Quote:

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Originally Posted by W2F a V-King

This motor should have t-stats and poppet with a two piece plates, correct?
James

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yeah.....

Rock is spot on. Temp gauge and water pressure gauge are a must. That motor should have the stock cooling system with stats and a poppet. The fact it has zero at idle makes me wonder if something has been messed with over time. Warren, jot down a good set of data before you change the water pump, including a reading on each bank from your infrared gun. Then, when you change the pump, jot down all the same readings again and report back.

If my boat only had 3 holes in the dash the only gauges I would want or install would be, temp, pressure and tach.
It is always a wise thing to replace your water pump kit ("COMPLETE" and the proper kit!) when purchasing or running a new to you motor.

Replaced water pump impeller yesterday. I did not get any data prior to swap out because I did not read Greg G's request prior to starting after church. Started motor on muffs and have 15 psig water pressure on cold motor. Thermostats started opening 130-140 F with laser shooting in random spots across heads. Due to different emissity areas tested with a device that is unable calculate this the readings are definitely not 100% accurate, but representative. After thermostats opened and water was flowing out exit hose pressure was 8 psig. Never moved motor out of idle speed so this gives me an idea that the impeller was definitely worn and not performing as it should have been. I will be installing temperature gauge and removing speedo during my new owner restoration. Took care of a few more items on my list by replacing all fuel hose back to tank and on motor. Tidied up all the wiring, replaced water separator filter, replace lower gear case lube and cleaned up motor inside the case.
How do I determine my type of gear case? Can I just count splines on prop shaft? Tlwjkw mentioned in his post since gear case had been changed? This lower unit only has 4 inlet water holes. I have owned XR4 & 6's and they had 7 or 8 holes I believe, not exactly sure. Son of this one owner boat/motor said that this how his dad purchased this motor out of the crate in 1994/1995.
Thanks for replies!

its possible!.. tha "little" gear case was an option on tha 150 PM but understand were VERY FEW ordered... if you had XR4/6 before 1995 that didn't have one then it had been changed sometime before ya got it unless ya live in a very strange part of tha world...........jmo

splines won't tell ya anything... 4 1/4 " vs. 4 3/4" will...........