Engine running hotter after new Raw Seawater pump installed, A Break In period?

JohnEGraham

JohnEGraham

Active Member
Aug 5, 2008
1,013
Long Island, NY.
Boat Info
250 Sundancer 1998 5.7.
Engines
350 Merc / Bravo 3
I was having an issue with the pulley screeching so it was time to change the impeller so I replaced the complete unit. Now the engine is running about 7 degrees hotter. My question is there a break-in period for the impeller to full seat? Has anyone have the same issue?
 
No break in period to my knowledge. Are you sure it was the raw water pump that was causing the squeaking? What is your water pressure at idle, 1250 rpms and 3000 rpms?
 
Hard to tell with out knowing pressures. Are you fresh or raw water cooled?
If fresh water cooled, would inspect the heat exchanger for blockage, and consider manifolds.
If raw or fresh water cooled I would suspect bravo-itis. This is when the hose that comes from the outdrive at the point where it comes thru the tramsom collapses and causes a restriction, Common in Br IIIs. I would inspect these things first, starting with the checking for the Bravo-Itis. Follow the hose from the pump input to the transom and romove to inspect. If it is clean and open, then move to the heat exchanger (freshwater cooled only) and make sure all of the water tubes are clean and free of blockages. Take both end caps off, you should be able to see thru it from one side out the other.
 
There is no break in period.

How are you measuring that 7* difference?
 
It sounds like the previous impeller let loose and some of the old parts have jammed up the new impeller. Belt squealing on the raw water pump means it can't turn the impeller.
 
JohnEGraham said:
I was having an issue with the pulley screeching so it was time to change the impeller so I replaced the complete unit. Now the engine is running about 7 degrees hotter. My question is there a break-in period for the impeller to full seat? Has anyone have the same issue?
Click to expand...

So the screeching was most likely just the belt. If you can hear an impeller you have got bigger issue. If you replaced the pump was it with an exact replacement? If not did you measure the diameters of the hose barb's?

The only way a new water pump would cause a temperature increase is if it is restricting the water flow some how. That how could only be the diameters of the barbs the hoses go on.
 
the screeching could be that the cam bearing in the seawater pump that actuates the fuel pump is dry of gear lube. pull the overfill screw on the pump and see if it has gear lube in it.
 
Nauti-Kal said:
the screeching could be that the cam bearing in the seawater pump that actuates the fuel pump is dry of gear lube. pull the overfill screw on the pump and see if it has gear lube in it.
Click to expand...
His engine doesn't use that style. Not all engines (and years) use the same style raw water pump.
 
Perhaps it is possible that the old tired pump was functioning as designed (although be it at less than designed efficiency), and now the new pump is collapsing the inlet hose in spite of the fact the the old one did not?
 
Play date has a point. Could be pieces of an old impeller, makes sense
 
Scott215 said:
Play date has a point. Could be pieces of an old impeller, makes sense
Click to expand...
Hense - Check downstream for blockage (impeller pieces and also debries) and check upstream for collapse (Bravo-itis) Without pressures its hard to tell which way to look. If pressures are high - upstream blockage / Low - poor supply (preload) usually due to blockage from bravo-itis or as mentioned incorrect sizing or type of input hose.
I have experienced both on my 496s. Bravo-itis and blocked up heat exchanger due to pieces of (not impeller) but shells and crap from that got in through the drive pickup holes.
To fix both - cleaned exchangers, oil cooler and pwr steering cooler with barnacle buster loop and installed thru hulls with blockoffs, strainers and drive showers. I considered this an upgrade and well worth it as it eliminates the crap getting in through the outdrive intake which play hell on the impeller, block up the heat exchanger, allow for replacement of impeller while in the water along with ample supply of water to the pump. If not doing through hull, would certainly recommend putting in a strainer.
 
Hi, I took it out again and the temps are back to the old values. I am not sure what caused it.
but The boat has been sitting at the dock for a while while replacing the risers and manifolds, There could be some slime buildup at the intake as suggested
John
 
Was your replacement Water Pump OEM? I learned the hard way to never skimp again!

PS - If closed cooling, you can back flush from the manifolds through the heat exchanger all the way to the pump itself (pull hose at Trans Cooler). Worked wonders for me. Bits of impeller and lots of RTV gasket material.
 
D Bell said:
Was your replacement Water Pump OEM? I learned the hard way to never skimp again!

PS - If closed cooling, you can back flush from the manifolds through the heat exchanger all the way to the pump itself (pull hose at Trans Cooler). Worked wonders for me. Bits of impeller and lots of RTV gasket material.
Click to expand...
Great idea!
 
So he replaced your manifold and risers before or at the same time as the water pump
 
JohnEGraham said:
Next long trip out the temp has now gone back to normal without doing anything…
Click to expand...
I'll speculate that you had some impeller debris in the cooling path that is no longer there. New impellers do create more pressure and if the debris is small enough .....it could have been pushed out the exhaust.
 
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