496 raw water pump problems
 

I have a 496 Mag with a Bravo drive. I had the impeller in the raw water pum changed now everytime I put the boat in the water I have problems getting the pump to prime unless I take off wide open as soon as I start the engine. After the pump takes prime its fine til I pull the boat out of the water then its the same thing again.

It seems that too many Merc 496 owners have problems after impeller change outs and the problem 90% or more of the time is from just replacing the impeller only on the pump without dealing with the grooving that can and does appear on both inside and plate end of the pumps. these groove is anything other that very slight in depth and quantity will cause the impeller not to seal properly at the ends and hence not be able to properly prime at start up and provide enough water pressure over the entire rpm band to keep the engine cool. There are now a few kits available that install stainless end plates in the worn housings with a special replacement impeller to correct this grooving problem. The only other items that can sometimes make priming difficult are, air leak on intake side of the hose, crimped small hose that comes thru Bravo drive at transom plate, or debris in intake or same Bravo transom water pass thru point.

link to water pump kit: www.jcmarinellc.com

Don't just plop in impellers without inspecting and making necessary repairs to the pump housing or replace the housing entirely.

Best Regards,
Ray @ Raylar

Agree completely!
 

I just put a new impeller in my 496mag ho brass housing and yes, I too have those scratches inside the housing (I knew it when I put in the new impeller-original housing, now 10 years old-not too shabby for brass and constant sand!). No problem priming but it seems like I too am dumping less water and the boat is running a little warmer than normal (running at 175 when running and can get up to about 185-188 it seems when coming back down on plane). I am going to either purchase a new housing or get the kit. I heard Captains CHoice in Ft Walton was working on a kit with same design per say but a slightly smaller impeller that would not require any modification to the factory bracket or silicone and such. I am going to wait a few weeks and then change.

Link to the kit (if still available): http://www.randrproductslakehavasu.c...pump_kits.html

rebuild kits
 

+1 on this kit.

I installed two of these kits (from JC Marine) in my 496's just yesterday. My originals were 8 years old!

After re-installing the pumps, I backflushed and then pre-filled the raw sea water system.

Did 70 miles on Lake Huron today. No problems at all. Good flow out of my exhaust tips, and steady engine temps of 160F.

I think you should investigate the repair kits in depth and ask the dealers that have installed them for some real world reviews.The whole reason we designed our new pump was we heard endless complaints about the fact that due to varying pump wear these plates could not always bring the pump back to its original performance. They would work initially just to fail prematurely. So as not to start a debate just make sure that the wear you have coincides with the thickness of the new plates. If you can get back to the OEM spec then great. But if your wear is in excess of the new plates then you cannot get the pump back to a OEM spec. I'm not saying the kits are bad it's just that providing two wear plates and an impeller for a pump with unknown wear will never fix all applications. Impeller crush or end clearance is what determines how well your pump performs.

If you're not that guy and you just want to buy these features incorporated into a new polished stainless steel housing then here's another option. http://www.hardin-marine.com/p-15774...d-502-mag.aspx

The other thing I see a lot of problems with is with the freshwater flush setups that some manufacturers install. Bottomline: The ones with the check-ball/spring system SUCK! They just get clogged up with sand/seaweed, and other crap, especially if you don't have sea strainers.

You don't need the check valve T-fitting in there, period. You just need a plane old T-fitting. You turn on the water hose, and it flushes from the T-fitting out the drive. Then start the engine, and water will be sucked into the impeller. It's that easy.

A friend on his brand new Baja had his get all gunked up, and another friend has what I believe to be the same problem on his 29 Outlaw as of yesterday.

All of the above is correct too. If the pump is even slightly scored, it's junk. The pumps are only about $100. IMHO, if you are preventative maintenance replacing impellers, just do the impeller and O-ring. Howerver, if you are recovering from impeller failure, replace the whole pump.

I just put in the kits from JC Marine and my historically crappy water pressure improved 100%. Pressures improved at idle and at speed. Engine temps no longer spike when coming off plane either.

Now, if there is evidence that this is a temp fix I will have to keep an eye on it. I'm just glad for the first time in many boating seasons I am starting out with good pressure on both motors.

Question for the Hardin Marine folks. Does that stainless steel replacement pump incorporate the quick drain valves of the factory unit? From the picture I don't see the dump valve?

Our pump accepts any of the seven different back housings they bolt to our unit just like the factory unit. So to answer your questions you retain that part from your original assembly.

I also had someone call today questions the mounting positions. Our pumps were designed from a clean slate so that when the wear plates were incorporated the mounting positions would be in there original location. We also chose to use the common mercury impeller that has been in every pump for the last 20 years. The original impellers use a larger stronger shaft. But the main reason was if you were in the middle of no where and needed a impeller you more than likely could find it since it is so common as the 496 impeller is tough to find in many places. Other than that it's just better materials and the incorporated wear plates that allow the pump to have a much longer service life.

Happy Boating

If your pump requires the re-use of the original rear housing how does that address the potential scoring on that side? It would seem that your pump only addresses half (roughly) of the problem of the scored pumps.

My OEM pump had scoring in the main housing and the back plate. And the shim kits cover both sides.

Am I missing something?

it has a new rear wear plate and a gasket that goes inbetween the old rear plate and new wear plate....i just bought one a few weeks ago and it works great with no modification whatsoever