Question on water pumps GPM.

[21270]

Could somebody tell me what the GPM for a Gen 2 water pump is, and what the GPM are on the raw water pumps found on the front of the late model Merc's.<br />I have tried diff web sites and still come up empty.<br /> Thank You!!!

 

[newport dave]

Re: Question on water pumps GPM.

From Mercruiser Service Manual #24 - pump outputs at 1000RPM<br /><br />Dave<br /><br />

 

[Don S]

Re: Question on water pumps GPM.

I'm not really sure it even has a published number. GPM's has a lot of determining factors, such as 4 cylinder vs. 7.4L, raw water or closed cooling, etc. Just the distance and volume (area of friction) all can slow down the GPM of a given pump. Along with RPM.<br />Since the 2 pumps work entirly differntly, comparing GPM's is not a good way of deteriming it's ability to cool an engine.<br />The Gen 2 pump is a floppy vane pump, only a few long vanes. Plenty of volume, LOW pressure pump. If you have a lot of cooling to do, it may not make it through all the systems and cool very well if there is a lot of heat to remove.<br />The belt driven pumps usually have lots of short vanes which give you slightly lower volume, but much more pressure. Which can overcome the resistance and extra heat put out by a full close cooling system and big block engines.<br /><br />After all that, what's your problem? maybe we can give you some clues as to a cure.

 

[Don S]

Re: Question on water pumps GPM.

Well, guess that answers the question if it's published or not.<br />Dave, is that out the exhaust or just from the in to the out of the pump?

 

[21270]

Re: Question on water pumps GPM.

Thanks newport dave & Don S, I appreciate the information. I will print this out and store it in the files.<br /> Thank You!!

 

[21270]

Re: Question on water pumps GPM.

Don S<br />I was just sitting here thinking if it would be better for my 1993 Merc 4.3LX (carb) if I was pushing more water through my full closed system. It was just a thought! I can run all day at 175 degrees with out a problem, with the Gen 2 pump. Just looking at the GPM.

 

[Don S]

Re: Question on water pumps GPM.

In general, Merc recommends going to a thru hull pickup and engine mounted water pump for a full closed system. BUT!!!!!! If you run in cold water (Puget Sound?) it's very common to run with the drive pump without problems. We see even the 5.7's up hear without the pump upgrade running with no problem, but our water seldom gets above 50°. With the 4.3, you should be fine. Just don't forget to change your raw water pump after 3 seaons.

 

[newport dave]

Re: Question on water pumps GPM.

Don,<br />I attached the rest of the page from the Merc service manual so you could see exactly how they want you to do the test. I have recently been working on cooling system diagnosis by visually monitoring raw water system flow and pressure. So far, it has been very helpful. Have you ever tryed somthing like this?<br /><br />Dave<br /><br />

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[Bondo]

Re: Question on water pumps GPM.

Way Cool Dave,...........<br /><br />Great Info I haven't stumbled accross til Now..........<br /><br />Do you have any #s or other resources for the psi.s that Should be seen on a New Clean system, Vs. a Rusted, Corroded system,..???....<br />In other words,.... How Much Pressure is Too Much Restriction,..???...<br /><br />I've been using the Clear Tubing trick for Years,....looking for Bubbles,......<br />Never thought of Adding the Ribbon to help with Flow Observation,,........... Great Idea,............

 

[21270]

Re: Question on water pumps GPM.

Puget Sound is correct Don S, (boating in the cold water). Like you said, It's a must to keep the raw water pump service up to date. <br /> Thank again!!

 

[newport dave]

Re: Question on water pumps GPM.

Bondo,<br />Thanks. It seems that there is really no diagnostic equipment available for raw water cooling systems and I hate to try to diagnose something by guesswork, so I came up with this. <br /><br />I have only tried it on 5 or 6 engines so far, so I have limited data. Have not tried it on a system with outlet (manifold/riser) restriction, so not sure exactly what to expect there. I have tried it on a system with an inlet restriction and saw very unstable pressure (needle moved rapidly back and forth between 0 and 25PSI. Normally you will see some flutter of the pressure gauge needle, but only a few PSI. <br /><br />I have noted that normal system pressure at idle tends to be about 2-4 PSI, and should reach 15 to 20 PSI around 3000RPM. The only other source of cooling system pressure data I have is what I have seen on newer engines that have OEM sea pump pressure sensors, where I have noted similar pressures.<br /><br />Dave