Raw Water Pump Impeller replacement - How to Guide

[tphinney]

I spent some time trying to figure out how hard it would be to do the Impeller replacement and could not find anything on the exact step by step instructions. So as a Newbie to do it yourself maintanence I though I would put this out for others that would rather spend a weekend bonding with their boat than shell out $200 bucks just to have the impeller replaced.

this is a compilation of the instructions out of the Solec manual and some short cuts I found by just doing it. these instructions apply to the Mercruise 5.0L MPI with engine serial numbers 6000XX and higher

Changing the raw water impeller for 5L MPI SRN # 6000XX

1. Loosen the serpentine belt.

Using a 5/8 box wrench and a 5/16 socket loosen the 5/8 locking nut so that the belt tension is removed and you can remove the belt from the raw water pump, alternator and tension pulley on the starboard side of the engine.

See Fig 1


2. Next step is to drain the water out of the engine. If you'r on a trailer or up on blocks now would be a good time to pull the drain plug out of the boat otherwise there is going to be quite a bit of water in the bilge. The first drian plug in on the bottom front of the engine on the port side (if you can’t get it to turn use a small wrench to start it). The next two are on the intake and out let of the Raw Water pump. If you want at this point you may want to take the water/fuel separator filter out to give you easier access make sure that you get the water drained from the raw water pump otherwise when you go to try to get the hoses off you’ll be fighting the vacuum created by the water in the pump [it toke be all day to figure this one out].

See fig 2 for the drain plug locations.

3. Once the water is drained you will notice the hose in the Figure 2 diagram which cradles under the water pump and connects to a 3 way splitter just above the water pump and next to the alternator. Go ahead and disconnect it now. This will make getting the whole assembly out easy.

4. Now its time to correct all the mercrusier diagrams on the web. See figure 3. note the double headed screw #15 and nut #16 in the diagram. they are shown in the incorrect location they should be shown in the location where screw #17 is and washer #20. Screw #17 is actually in the lower hole not the top one. These screws and nuts not only hold the raw water pump assembly in place but also hold one end of the bracket for the starboard side tension puller. To get these out you will probably need a Swivel/U join socket adaptor to get the clearance you need to break them free. Once these are free the whole bracket should drop down; but you won’t be able to get it out yet.

fig 3

5.Next you will need to loosen the nut below the alternator which supports the starboard side tension pulley mounting bracket. Note Fig 4. once this is done you can swing the tension pulley and it’s mounting bracket out of the way.

fig 4

6.Now comes the hardest part. Loosen the clamps on the intake and exhaust hoses for the raw water pump and remove the hole assembly.

see fig 5

7.Now that you are out of the bilge it’s time to remover the raw water pump from the mounting bracket. All you should need is a 10mm socket/wrench to pull the 2 bolts from the rear of the pump and the 1 from the top of the pump. Then remove 4 remaining bolts on the rear of the pump and pull of the back of the pump.

see fig 6

8.Now comes the time you’ll need a special tool if you want to make this easy. If you have an impeller puller use it to pull the impeller (see figure 7) out of the case; if not go to the nearest boaters world and get one. Remember the rotation angle of the impeller that you pull out as the new one will need to go back in the same way.

fig 7

9.A little bit of soapy water will help get the impeller in the case. Then replace the O-ring on the case with the new one in the impeller kit and put the raw water case back together again. The bolts on the raw water pump and the raw water pump to mounting bracket should be tightened to 8.8ft-in.

10.re install the intake and exhaust water hose’s to the raw water pump and tighten the hose clamps and drain plugs

11.mount the raw water pump and starboard tension pulley mounting frame to the engine block and torque the bolts to 30ft-lb.

12.re attach engine hose which runs under the raw water pump.

13.tighten the tension pulley mounting from under the alternator.

14. re-attach the serpentine belt and retension so that it flexes no more the 1/4 of an inch at it widest span between pulleys and tighten.

15. drop the boat in the water or put on the muffs and watch you water PSI and/or temp. the water PSI will read really low at first because the engine has been drained, but it should be fine in a coule of seconds.

At first attempt it toke me 2 full days to get this done which also included getting the right tools. and figuring out how to get at certain part. next time I figure I could ge this done in about 30 minutes.

they way I Figure even with having to buy the impeller Kit, the Impeller puller and a torque wrench it still cost me less than having the dealer do it. next time my only expense will be the $34.00 for the kit which sure beats $200+

hope you enjoy the post

 

[Four Suns]

very nice write up!

Personally, I believe keeping the engines cooling system in tip-top shape is the most critical and hardest part of boat maintenance. I see how people brag about changing the oil every 50 hours but not give the impellers, strainers, and risers a second look.

Great job!

 

[tphinney]

thanks Gary;

I hope to do a series of these as I look at doing most of my own service to reduce my operational cost. Plus it will give me a complete inventory of tools and parts I should keep on board incase I break down on the water.

 

[wish2fish]

it is a nice write up. When my pump went out last year is was a humid 95 degrees. I elected to have it done by the local mechanic.

How much room do you guys have to get at this pump? There is little to no room for me to get my arms in there!

 

[tphinney]

wish2fish;

the room issue is the reason why I wrote the post. between the water seperator and the engine mounting bracket there really is no room to come at this from the side as most instruction sets that I have found try to tell you.

on my boat there is enough room starboad of the engine to put either a waste holding tank or a generator. and in front of the engine there is about 1 may be 2 feet from the front of the engine to the gas tank and freshwater tank which are stacked up on top of each other. worse yet from the front of the water pump I only have about 6 inches to get at the bolt that hold the mounting bracket for the water. This is why I need a Swivel/U-joint for my socket set; so I could come out and then angle up or to the side to get the leverage I needed.

If you follow the instructions and come at the problem from the front and clear out the blet, mounting brackets and hoses you get enough room to loosen the hose's of the raw water pump and take the whole assembly out of the bilge to actually do the impeller replacement.

If you want I'll take a snap shot of the engine compartment next time i'm on the boat if it will help.

 

[Gunn]

Now this is the kind of information I love to see on this forum! Very understandable, and easily read how-to guide for -anyone- to do this.

I've populated my entire garage and woodworking shop on the premise that for the cost of the tools and the parts, I could still do it cheaper than having someone else do it, or buy it. And its true. It may take me more time, but...I'll get it done. :wink:

Great job; look forward to more... (even if I don't have a small block V8...YET).

 

[Dave S]

Nice write up. :thumbsup:

The newer 350 MAGs, such as the one I have on my boat, have brass water pumps instead of the plastic ones. I will be doing mine for the first time in the next 6 months or so. On the 350 MAG engines, it looks like it will also be necessary to loosen the fuel cooler to have enough room to get to the pump. And since the pump is different, there may be some other things that need to be done a bit differently also.

 

[tphinney]

Dave;

On mine the raw water pump wasn't plastic, but actually seemed to be cast iron and unlike the diagram in Fig 3 (which came out of one of the service manuals on line ) it didn't have anything on the back of the pump except for the intake and exhaust hose fittings.

So our setup might be more similiar than not.

 

[topgun1185]

My water pump bearings let loose after only 2 years and 200 hours. Recommeded service is 3 years or 300 hours. I don't think changing the impler is wise I changed the entire pump especically since by bearings failed. i now carry a spare pump. I have had boats for years with jabsco raw water pumps and never had this kind of failure. These merc pumps are complete garbage in comparission. Also the previous post is accurate for pump/impeller change. Just another example of the poor design you have to remove the belt and entire pump to service the impller. What a joke. By the way even though I had full warrenties the raw water pumps are not covered. Any one else have raw water pump problems.

 

[280 SeaRay]

Tom... fantastic job on the write up. You may want to mention this is a Bravo water pump setup and does not apply to Alpha configurations. I had planned to capture the entire alpha proceedure this year and write it up here as well.

 

[barryg]

How much is the raw water pump for the 350 Mags?

Barry

 

[Chris R]

I think what's baffeling to me, on this entire subject of impellers, is this is nothing more than a water pump (in my mind). Imagine if we had to pay as much attention to, and work on the water pumps in our cars, as much as with these engines. Can you imagine having to replace the water pump this often on any newer model car??!! Not really apples to apples, of course, but geeze, you think they could design something that was a bit more dependable.

 

[topgun1185]

I agree the merc water pump design is terrible. Servicablity and durablity for such an important item is just wrong and certainly not up to par with alot of other brands. As far as cost from a dealer around $325.00 currently they are ebay for $130.00 delivered with pully. I just bought a spar since when i had my failure none where avaiable.

 

[Four Suns]

It's not really fair to compare a raw water marine pump to a car engine cooling pump. The design requirements of cooling a marine engine are different than cooling a car engine with an air-cooled radiator. For closed loop cooling system, there is the typical centrifugal cooling water pump for the internal engine coolant and it gives very little trouble just like a car. However, when you have to deal with all the head pressure issues and water that can have debris in it, a positive displacement pump is needed hence the rubber impeller design.

We actually had some discussion a while back about if a rubber impeller is a true displacement pump as the back pressure gets really big (like a clog or blockage) but at the end of the day, it's probably the best design for this type of application. Now why Mercury took the cheap way out and essentially mounted the raw water pump backwards just so it can access the belt is beyond me... other than to save money on it...

 

[topgun1185]

Amen. I thought for a minute you were going to agree with their design. I do agree it's not fair to compare to a car water pump.

 

[rondds]

your raw water pump has no automobile equilavent. cars use air to cool the coolant, not sea water. BUT boats have a circulator pump, just like a car. and those are fairly maintainence free - or, should i say they dont need attention every 2-3 seasons. also of note - crusader now uses a stainless impeller for raw water pick up and they are not NEARLY as tempermental as our mercs.

i didnt see the step in those instructions where it says "use a shrink ray to get yourself small enough to fit btwn the engines and the bulkhead." also didnt see the step that says "keep your chiropractor on speed dial since you will no doubt be in traction for a week after struggling to get to the bolts and hose clamps by hanging upside down in the engine room for 2 hours." this job is obscenely easy, IF you have good access to removal of the pump. ACCESS IS EVERYTHING!

 

[Chris R]

Again, I do understand these are not the same as a comparison; however, my observation is nothing more than amazement at how the industry just seems to think it's "OK" to have a (somewhat) critical engine component such as this not last very long. Seems technically archaic IMO.....

 

[Nehalennia]

Again, I do understand these are not the same as a comparison; however, my observation is nothing more than amazement at how the industry just seems to think it's "OK" to have a (somewhat) critical engine component such as this not last very long. Seems technically archaic IMO.....

Because they need $200 out of all us on a regular basis.

 

[NautyDog]

THANK YOU....

..for this thread. It would have taken me a day or two to figure this out and then re-do it again after my mistakes. I was able to do my port engine in about an hour my first time - and most of the time was spent on the hoses.

I would like to add what I learned on this.

I didn't need to remove anything extra except the Fuel-Water filter. I just removed the 3 bolts for the bracket, and the hose clamps. (I didn't remove the starboard side tension pulley mounting bracket). It was tough getting the two main hoses off (even with the water drained). As with any hose removal, there are two things that help - 1) I carefully used a flat head screwdriver to break the seal around the edge and 2) try twisting the hose until you feel it break loose (this was hard on the two big hoses). Even with these tips, it was still tough. Broke a few knuckles getting off those hoses.

But BEFORE you start, get yourself a set of these - they are Flex ratchet Wrenches that they sell at Lowe's, Sears, Advanced Auto, etc. You can get just the 10mm one ($12) or the set for $60 depending on which brand you get. They REALLY help getting some of these bolts. off.

Also, I used Silicon grease on the O-ring. You can get this from a dive shop, or order it online. It helps create a good seal, and keeps the O-Ring flexible so it keeps a good seal. Petroleum based products (i.e. Vaseline, grease, etc) will turn the O-ring into goo after a few years.

 

[Nehalennia]

Tom. The link's images dried up. I'd sure like to have a look at this again.