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water pressure gauges

Checkm8fan

Member
I have heard now from two sources that the V6 Merc's have problems with hot spots
developing.
When this happens it turns the cooling water to steam and this will cause your water pressure gauge to read an increase in pressure.
This is a false reading of course, as it is now reading steam pressure.
This happens unfortunately just before you burn a piston.
I was told this by a workmate who had to rebuild a 2.5L ,175 HP. and also by an ex Mercury employee.
I cannot give any more details ,RPM's speeds etc. as I do not have the information.
I do know that my workmate was on a high speed,wot run when his engine failed.
 

Checkm8fan

Member
I have heard now from two sources that the V6 Merc's have problems with hot spots
developing.
When this happens it turns the cooling water to steam and this will cause your water pressure gauge to read an increase in pressure.
This is a false reading of course, as it is now reading steam pressure.
This happens unfortunately just before you burn a piston.
I was told this by a workmate who had to rebuild a 2.5L ,175 HP. and also by an ex Mercury employee.
I cannot give any more details ,RPM's speeds etc. as I do not have the information.
I do know that my workmate was on a high speed,wot run when his engine failed.
 

175checkmate

Moderator
Staff member
It really depends on where you tap in to get your reading. I have my pick up for the gauge taped in to my water discharge line. This gives me a reading after the water has run through the engine.





1975 Checkmate Tri-mate 2, 2.4 200+ / Sky jacker 6" plate / 25p Laser 2 prop, Currently the boat is undergoing overhaul.
 

TMR

Member
It really depends on where you tap in to get your reading. I have my pick up for the gauge taped in to my water discharge line. This gives me a reading after the water has run through the engine.





1975 Checkmate Tri-mate 2, 2.4 200+ / Sky jacker 6" plate / 25p Laser 2 prop, Currently the boat is undergoing overhaul.
Would appreciate some help.

I have a 1996 Mercury 225 EFI motor. I would like to install a water pressure gauge in the boat.

Where is the best location to pick up on the motor to get an accurate reading of water pressure?
 

TMR

Member
Thought I should post to help the next person looking to install a water pressure gauge on a 1998 or earlier 3 liter V6 Mercury EFI motor.

Use the Mercury 0 to 15 psi gauge kit Part Number: 79-895288A01
Don’t use the more common 0 to 30 psi kit.

The npt plug that needs to be removed to connect the pressure hose from the gauge to the water pressure tap location on the motor is located at the very rear of the motor just a bit lower than the seal area where the motor cover sits. It is a little hard to see at first.
 

1954bmw

Active member
Why do you recommend the 0-15 versus the 0-30, I have had inline sixes make over 15 pounds of pressure???
 

TMR

Member
Why do you recommend the 0-15 versus the 0-30, I have had inline sixes make over 15 pounds of pressure???

The Mercury service manual lists a spec for the V6 3.0L of 8 to 10 psi at 5000 rpm.

I purchased the 0 to 30 psi water pressure gauge kit originally. The front of the box shows a note listing all of the motors the kit applies to and reads “except for 3.0L V6 1998 and earlier”

The front of the box for the 0 to 15 psi kit shows a note indicating for use with “3.0L V6 1998 and earlier”

I think the 0 to 30 psi gauge would work if you don’t mind the needle staying in the lower quadrant of the gauge.
 
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