"Water Pressure 101"- Poppet Valves and Variables with Water Pressure

[Allsup]

Thanks

[tax man]

A lot of great information. I have a 32 foot cat with twin 2011 300XS. I put about 190 hours on the boat with no water psi issues. I now have a water psi issue with the port motor. If I am running with the current and down wind, the psi on the port motor will drop to 5-7 and the temp will increase. If I am going in to the wind I get enough bow lift and water psi is around 15. No issue with the starboard motor. Any suggestions?
Thank you

[EuropeanAM]

A lot of great information. I have a 32 foot cat with twin 2011 300XS. I put about 190 hours on the boat with no water psi issues. I now have a water psi issue with the port motor. If I am running with the current and down wind, the psi on the port motor will drop to 5-7 and the temp will increase. If I am going in to the wind I get enough bow lift and water psi is around 15. No issue with the starboard motor. Any suggestions?
Thank you

Welcome to BBC!

It's always best to start at the SOURCE: The Water Pump.

In your case... while replacing the water pump, make certain that you inspect the passages BELOW the water pump (especially those that run forward to the low water pickups in the nose of the gearcase).

43026Q06 (Kit WITHOUT housing)
817275A08 (Kit WITH housing)

Debris in this area can cause intermittent loss of water pressure.

[tax man]

Thank you. I did replace the water pump but it did not help. Also swapped gear cases to see if the problem would move to the starboard motor. The issue stayed with the port motor. So I think the issue is somewhere above the gear case.

[Jonesy23]

Don can give you more info than me but I had a psi issue with my port motor after running aground on a sandbar, luckly I was only at idle speed. The water pump was in good shape so I pulled the poppet valve and found some debris in it, the debri had also torn the diaphram. Ordered a new one from Don and all was good after.
What boat do you have?

[EuropeanAM]

Thank you. I did replace the water pump but it did not help. Also swapped gear cases to see if the problem would move to the starboard motor. The issue stayed with the port motor. So I think the issue is somewhere above the gear case.

I would then move on to inspecting/testing thermostats, and POPPET VALVE REPLACEMENT.

[Wilbur]

I would then move on to inspecting/testing thermostats, and POPPET VALVE REPLACEMENT.

Regarding poppet valve replacement. Do you replace the entire assembly or are there rebuild kits? What part numbers would I be looking for? 1997 225EFI s/n 0G539853.

[EuropeanAM]

Regarding poppet valve replacement. Do you replace the entire assembly or are there rebuild kits? What part numbers would I be looking for? 1997 225EFI s/n 0G539853.

Contact Rhonda in our Parts Department.... she has an "internally packaged kit" for your 3L model.

See Rhonda's sticky post at the top of the forum for ordering information.

[AZboatscope]

< Mod Edit>: Please see the Forum Announcements, and open a separate thread for your engine. Thanks!

[DundeeMike221]

Where did you get the new face seal from? This may be the cure for my 250XB....Thanks, Mike

[EuropeanAM]

Sticky: If you want to order or price Mercury Engine Parts or Accessories...

[otrdriver2002]

I have a 95 225 efi. Just replaced the lower unit with a used one from a 98 225efi. I also replaced the water pump. After putting the muff on it and hose I am getting good pressure and flow out of the telltale. It will shoot it out over 3' at idle. BUT I have NO water coming out of my pressure gauge hose. Cut and spliced the hose about 1 foot from where it going in the lower unit and I can blow through it but still no WATER flow even after motor warms up. I can fill the telltale water change from cold to hot so I'm sure the Tstats are working. Should I get water flow to the gauge at idle on the hose? I also ran it up to around 1800 after Tstats opened but still no flow.

[JOE54]

doesnt go in lowerunit goes in powerhead base of block beside telltale fitting

[EuropeanAM]

^^^^ +1

That hose coming from the gearcase is the Pitot (Analog SPEED) tube.

[basspro57]

Hi Don...I have been dealing with this for a long time on my boat. I am running close to 30PSI at WOT on my Champ 198 with a 225ProXS. Its not overheating and I know its not "steam pressure". Let me first ask, why is pressure higher than 25psi a bad thing? My buddies say if the water pressure is too high then there must be a concern about that being steam pressure and not water pressure (and the motor is overheating). Just trying to understand why water pressure of 30 at WOT would be a problem (using 30 psi as an example). What is the desire to keep it to 25? Is that because if the pressure is higher than 25 then the poppet valve opens (that where I believe you said the thermostats are no longer effective) meaning that the water is no longer cooling the cylinders (just going out the poppet valve and not flowing through the motor properly)??? Again...just trying to understand the problem with having high water pressure as I have this exact problem on my boat/motor setup (at the current motor height). I am going to install a hydraulic jackplate in the spring. I am concerned that if I raise the motor too high to reduce the water pressure, then I run into the performance problems associated with the motor being too high. Very interesting discussion and I totally understand the ram pressure theory as I thought this is exactly what was happening on my particular boat. I really was not concerned about the pressure being high cause the motor wasn't overheating (but now you have me thinking).

[EuropeanAM]

Hi Don...I have been dealing with this for a long time on my boat. I am running close to 30PSI at WOT on my Champ 198 with a 225ProXS. Its not overheating and I know its not "steam pressure". Let me first ask, why is pressure higher than 25psi a bad thing? My buddies say if the water pressure is too high then there must be a concern about that being steam pressure and not water pressure (and the motor is overheating). Just trying to understand why water pressure of 30 at WOT would be a problem (using 30 psi as an example). What is the desire to keep it to 25? Is that because if the pressure is higher than 25 then the poppet valve opens (that where I believe you said the thermostats are no longer effective) meaning that the water is no longer cooling the cylinders (just going out the poppet valve and not flowing through the motor properly)??? Again...just trying to understand the problem with having high water pressure as I have this exact problem on my boat/motor setup (at the current motor height). I am going to install a hydraulic jackplate in the spring. I am concerned that if I raise the motor too high to reduce the water pressure, then I run into the performance problems associated with the motor being too high. Very interesting discussion and I totally understand the ram pressure theory as I thought this is exactly what was happening on my particular boat. I really was not concerned about the pressure being high cause the motor wasn't overheating (but now you have me thinking).

Normally this would be a question for a separate post, specific to your engine.

Make sure your gauge reads ZERO with the engine OFF. If it does not, then you cannot believe any figure it provides, at any speed (replace it).

In short, the job of the water traveling through your engine is to absorb and remove the heat being generated by both moving components AND combustion events (explosions). In order to absorb the energy/heat, the water must actually occupy the cooling passages for long enough to accommodate the transfer. Water PRESSURE is often a good indicator of how fast the water supply might flow THROUGH the system (think of pressure as "potential flow" for discussion purposes).

You can get a reasonable idea or correlation by using a cast-iron frying pan to cook some eggs. Splash water across it at high velocity and then put your hand on the pan. Ok, NOT REALLY, that's gonna leave a mark!

BUT... if you submerse the pan in water for 5-10 seconds, now you've absorbed and removed a considerable amount of the heat from the pan. Same basic principle for the water traveling through your engine block. Too little: the engine will overheat. Too much: The water can't efficiently remove the heat it needs to.

Just something to think about... it's not "just" the mechanical or setup problems that "could" cause high pressure... it's also making sure that the cooling system can function efficiently.

[basspro57]

Got ya...thanks for the explanation Don. Happy New Year!!!

[dblume]

Add me to the list of questions. Two weeks ago I noticed my motor was only warming to 98 degrees when running. I got home and checked the thermostats both did have sand holding them open. I cleaned them and went to the lake the next week. On start up the engine got to 138 then the thermostats opened and motor lowered to 120 to 125. Which is normal for my motor. Idle psi 1.6 running max rpm 25ish. But while running wot the smart gauge shows temp at 107. I got home checked thermostats and they were clean and closed. Next week same thing. Heats up opens and runs 120 to 125 but only 107 at wot. Is there a problem, if so is it the popit valve?

[dblume]

That was in 55 degree lake water and about 70 degrees outside.

[Bryanmc57]

Running down the lake the poppet valve opens and water basically free flows through the engine bypassing the thermostats. What you are seeing is perfectly normal. The 1.5 psi at idle is about 1 psi low. Probably time to rebuild the water pump.