Mercruiser 8.1 raw water pressure - typical?

paulswagelock said:
Anyone have any actual experience with the Hardin. Several people recommend it, but I haven't found anyone that actually has one.
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Yep. I bought two last year and installed them prior to heading out for the 2014 Atlantic City Rendezvous. About 8 hours up the Bay the one on the port motor failed. I limped into Annapolis on a single motor, got up at 5am the next morning and put the Merc pump back on.

Hardin replaced it under warranty.

At the beginning of this season, I reinstalled the Hardin pump. I made a trip to Solomon's and when I got back the port pump and the starboard were both making a squealing sound. I yanked them both off and put my Merc pumps back on.

I sent the pumps back to Hardin and they are unable to determine the cause of bearing failure. As a result, they have decided to issue me a credit for the two pumps and I'll continue to run the Merc pumps.
 
sporters78 said:
Since when do harley mechanics get $200 an hour ? I think you're full of BS and this used to be a friendly Forum. Just my rant as some of the posts lately have been on the mean side.
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HD= heavy duty... We actually hit 245/hr on OT. That is Canadian funds too by the way. Sorry if I offended anyone. That was not my intentions. I don't know either parties but suspect some on here may. Negative comments if deserving are what they are. If not then can negatively inpact an individuals reputation. Again I apologize.
After reading this thread I would also bet that the new pump is not going to fix anything. Centrifugal pumps are supposed to make flow and not pressure. Yes any flow with any kind of resistance will create some kind of pressure but that is not what they are really designed for. The op sais there is good flow coming out the exhaust which kind of tells me the pump is working. I would be checking for temp drops across the exchanger (assuming there is one) and figuring out whether the problem is in fact in the raw water side or possibly the fresh.
Will leave this thread now and good luck to all!
 
mistercomputerman said:
Yep. I bought two last year and installed them prior to heading out for the 2014 Atlantic City Rendezvous. About 8 hours up the Bay the one on the port motor failed. I limped into Annapolis on a single motor, got up at 5am the next morning and put the Merc pump back on.

Hardin replaced it under warranty.

At the beginning of this season, I reinstalled the Hardin pump. I made a trip to Solomon's and when I got back the port pump and the starboard were both making a squealing sound. I yanked them both off and put my Merc pumps back on.

I sent the pumps back to Hardin and they are unable to determine the cause of bearing failure. As a result, they have decided to issue me a credit for the two pumps and I'll continue to run the Merc pumps.
Click to expand...

Can't believe I am reading this. I was just about to order one with the pulley. Did you press your OEM pulley on or by one with pulley?
 
Went with the new OEM pump. Tested it out today. About 1.3 psi at 600 rpm, 8.5 psi at 4000 rpm.
Engine did not go into guardian or overheat, so I assume all is good. Looked at the old pump- it is certainly scored.

Is it possible my pressure sensor is not reading right also? Do they ever fail where they work, but they are just inaccurate? If so, does cleaning it out work, or just replace?

also, mechanic only is billing me for the pump and the labor to change it, not the impeller and labor - his suggestion. Said no need for me to pay for missed diagnosis.
 
Update:
I put a gauge on and verified the pressure to be accurate.
I had the drive pulled today to do the service (bellows, bearing, shift cable, water inlet tube, trim senders, seals). The water inlet tube was reduced in size considerably, some corrosion, but mostly from the collar being deformed (almost looked melted). Will see how the pressure is later this week when put it back in the water, but I expect to get the 14-15 psi at high RPM that I expected from the new pump.

BTW - marina charging $1250 for the job - seem fair?
 
A BIII dosent use a water inlet tube. uses a hose with expanding inserts on both ends.
 
Yep, that is what I was calling the water tube - shaped hose, ~3/4" diameter, plastic insert on each end.
 
Readings I saw a couple of years ago. These numbers you guys are getting seem lower, unless it's a different sender or location (?) One is port, one is stbd - not sure which was which.
100_3978_zps1fe76bf7.jpg


100_3980_zps732517be.jpg
 
Splashed back in. Now I have 21 psi at 4500 rpm. That is more like it.
 
Keep in mind that psi. has nothing to do with flow and has every thing to do with resistance. So unless your certain you have nothing obstructing the water exiting your engine, like old risers, the psi reading doesn't mean much. Flow is more important than pressure. High pressure can be an indication of blockage down stream.
Base numbers, from a new boat would be helpful.
 
Passages are all checked and perfectly clean. Heat exchanger is spotless. So, in my case, removing the inlet restriction does increase flow which I measured per Mercs recommendation. I flow more than required.

And if Cv remains constant, flow is proportional to the square root of delta p, so in my case, all else remaining the same, increased inlet pressure does mean more flow since Cv and outlet pressure remain the same.
 
I had the same issue installed new oem pump pressure dropped. Installed complete transom kit including you designed water hose. this is a pic of the blockage I had at transom at housing.
PXL_20230320_190733424.jpg
PXL_20230320_190733424.jpg
 

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