CAT 3208 impeller questions

Still in my 1st season of owning first big boat. It's in heated storage now.
I wanted to inspect/change impellers for next season so I pulled the whole water pumps off for access. It's the only way you could get at the Stb. side. And that was after removing the fan belt cage. Once you have the pump in hand you can change the impeller although this isn't exactly an easy procedure either (but I did get it).
If I have a failure underway my thought is to have a spare pump ready to throw in. Questions: Is it ok to let the impeller sit in the pump over long periods of time? Do you change your impeller seasonally? Would it be ok to install the impeller now with launch not until mid May? It does seem like these Sherwood impellers are manufactured well but what is the life? My impellers appear good after about 1 season and 225 hours. What do you you lubricate the impeller with at installation? Vaseline? Dish Soap? On your first start after spring launch is it sufficient to just make sure the raw water strainer is full of water or do you have to prime the pump. Looks like there is a plug on these pumps that could be used for priming.
Appreciate the feedback as always.

I'd say they are fine waiting for Spring. The impeller in my ski boat sat for several years and with a dry start, no issues. Not the best idea but I finally changed it and while it wanted to keep the shape of the pump it was still working. I also have 3208s. I would not worry about waiting for a several months and dish soap sounds about right for start up. My pumps are accessible so I can change the impeller without removing the pump.

I do what u are planning for a similar reason. Spare pump has the impeller mounted. Do not use petroleum based lube on the rubber impeller. I use silicon based (dielectric grease) for the spare(stored) pump. If just changing the impeller on the fly, glycerin or dish soap work fine. Or, once the face plate is reinstalled, pull the top hose and pour some water into the pump

On our last boat one of the water pumps was really difficult to get to. The impeller was almost impossible to get changed. The mechanics where it had been maintained for 15 years said they usually pulled the pump to change the impeller. I found a tool at impellertool.com that made it pretty easy to change the impeller. I could do it in 20 minutes. No affiliation.

I know some people change impellers frequently but I've never understood that. I know impellers can fail, so I ALWAYS confirm waterflow after engine start, but frankly I've never had an impeller fail. I find the shaft seals tend to fail first. When I've pulled old pumps off my 3208s apart the impellers have always been fine.

Like you though I carry a fully rebuilt pump ready to install. As I said though, the mode of failure I've encountered is shaft seals. Usually they just drip but I have had them start start to spray water all over the engine room.

3208 impellers turn really slowly, have little suction head or pressure head, and therefore last for years and years in full keel recreational boats that rarely pick up silt or sand. I would not worry about it. Just check the strainer often and make sure there is flow when you start the engines.

I change my impellers every 5 years or 500 hours. Seams like a waste but I do it anyway. I have replaced both my pumps once, time unknown, both suffered seal failure.

Great info guys. Thank-you all. Based on your responses, and my observations, I feel comfortable in re-installing these "1 season used" impellers back in the pumps and then installing the pumps back on the engine soon.

I had a whole brand new Sherwood pump as a running change because one of the pumps on my 3126B’s was hard to get to. It shipped with a brand new impeller and I don’t know how long it was on the shelf but the base of the blades had cracks in them. Luckily I wasn’t in a hurry and just popped in a new impeller before I fitted it. I always grease the pump housing, shaft and cover plate with Lanolin Grease before I replace the impeller. Makes them easy to get in and out and keeps the impeller in good condition. Apart from obvious damage, pushing the blades over and looking for cracks along their base is a good way to avoid a failed impeller. That and not plowing through the bottom of course!

Q ..."impellers are manufactured well but what is the life?"

A ...'last for years and years in full keel recreational boats that rarely pick up silt or sand.'


Changing impellers a big hassle is removing the slotted screws from the cover.

A few bucks at a hardware store will get Allen head SS machine screws, and a few wrenches to fit.

The box of 100 allows for dropping in the bilge or sharing with an other boater.

It takes me less than ten minutes to remove my 3208 pump assembly, most of that is the four hose clamps, then the two bracket bolts. Removing as a whole assembly, IS, the quick way for me. I suppose if you are doing it the first time it might seem the hard way, but the size of the assembly is what makes breaking the hose seals easy, since you have oversized leverage, it comes right off. Once off, you can nicely lay it flat and remove the pump cover, then just use an impeller puller(get one if you don’t already) and you are done. I find the whole operation one of the easiest on the boat. Don’t waste your time trying to work on engine where it is hard to get at.

I’ve only had to replace seal/bearings once about 16 years ago when I bought the boat. If seals are going frequently, I’d suspect a bad bearing or shaft causing wobbling.

I do have a spare pump somewhere, but never used it and I don’t think it has both a bracket and a pulley. THAT and the bronze elbows are a bigger job than rebuilding the pump, which I also have rebuild kits for somewhere. So it’s really more of a fail safe than time savings. To make for a component swap you need the entire assembly and spare brackets are surprisingly scarce.

Impellers are cheap, if you have spent the expensive labor to remove, replacing the impeller means you don’t have to touch it again for some time. You were worried enough about the amount of effort to replace the impeller, but want to save money and put it back. I’d zero the hours and direct my future effort elsewhere. It’s about the time, not the part for me.

I have the 3208-375th it came with all of the repair and parts manuals you need just send me a note and I’ll copy them for you.
I may also scan them into a pdf file.

Fellow Mariners with CAT 3208s,

We have owned our boat for several years and having come from an aviation background where preventative maintenance was the key to reliability, I am now questioning my need to change our impellers as frequently as I do.

We are not full time live-aboards however we transit the Tombigbee annually from the Tennessee River to the Gulf Coast.

I don't carry a spare water pump (considering this option now) but I do change my impeller annually along with all fluids (engine oil, transmission oil and engine coolant).

There are postings that claim a 5 year interval and these impellers never fail.

Am I being too overly protective of my impeller?

I do remove the pumps when I change the impellers, but am I making this a bigger deal than I should?

Thanks for your comments,

Rusty Bliss
M/V Kristine
DeFever 53 POC
Iuka, MS

After collecting 6 near perfect used spare impellers I decided to not be so preventative. On the other hand it doesn’t hurt to be preventive. What ever helps you sleep at night.

tiltrider1 said:

After collecting 6 near perfect used spare impellers I decided to not be so preventative. On the other hand it doesn’t hurt to be preventive. What ever helps you sleep at night.

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You are correct... do whatever helps you sleep! I guess it's a "belt and suspenders" thingy! I may "extend" my replacements.

Stay warm, stay healthy,

Rusty

Pat T said:

Still in my 1st season of owning first big boat. It's in heated storage now.
I wanted to inspect/change impellers for next season so I pulled the whole water pumps off for access. It's the only way you could get at the Stb. side. And that was after removing the fan belt cage. Once you have the pump in hand you can change the impeller although this isn't exactly an easy procedure either (but I did get it).
If I have a failure underway my thought is to have a spare pump ready to throw in. Questions: Is it ok to let the impeller sit in the pump over long periods of time? Do you change your impeller seasonally? Would it be ok to install the impeller now with launch not until mid May? It does seem like these Sherwood impellers are manufactured well but what is the life? My impellers appear good after about 1 season and 225 hours. What do you you lubricate the impeller with at installation? Vaseline? Dish Soap? On your first start after spring launch is it sufficient to just make sure the raw water strainer is full of water or do you have to prime the pump. Looks like there is a plug on these pumps that could be used for priming.
Appreciate the feedback as always.
View attachment 124179

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Do not use Vaseline it is petroleum based and will destroy the fins - new impeller should come with its own lubricant

On my 3208T/As, I change the impellers annually while doing preventive maintenance and then keep the best "used" one as a spare part. Impellers are cheap for CATs.

I'd say a LOT of the timing has to do with the channels that you travel. I took a long trip up the Ohio River last summer (highly recommend) on new impellers, but nearly every marina had very tight water and my own marina on the Cumberland was also kicking up milk shakes. So, after those 225 hours, I will change mine and will take a good look at them to see if the silt did much damage.

I do carry a spare pump, but not for an impeller change. I do it because swapping seals or bearings in the field is not ideal (though it actually can be done pretty effectively if needed so long as you have parts). Those pump kits usually don’t include all the seals anymore you usually need to order them individually, so make sure you actually have them all. This is actually the main reason for having a spare pump ready to go.

There is reasonably little to go wrong with an impeller swap. If you have to pull the pump off anyway (and that’s the way I do it too), just throw a new impeller in it, that part only takes about ten minutes. I don’t store an impeller in my spare pump (well actually I do, I just don’t plan to use it).

Also, consider that to swap to the spare pump, that means mounting the spare to the bracket (so the bolts might snap, I might have to chase the threads with a tap and really I should carry spare bolts) and I’m going to have to swap the pulley as well.

ghost said:

I do carry a spare pump, but not for an impeller change. I do it because swapping seals or bearings in the field is not ideal (though it actually can be done pretty effectively if needed so long as you have parts). Those pump kits usually don’t include all the seals anymore you usually need to order them individually, so make sure you actually have them all. This is actually the main reason for having a spare pump ready to go.

There is reasonably little to go wrong with an impeller swap. If you have to pull the pump off anyway (and that’s the way I do it too), just throw a new impeller in it, that part only takes about ten minutes. I don’t store an impeller in my spare pump (well actually I do, I just don’t plan to use it).

Also, consider that to swap to the spare pump, that means mounting the spare to the bracket (so the bolts might snap, I might have to chase the threads with a tap and really I should carry spare bolts) and I’m going to have to swap the pulley as well.

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When I pulled the pulley off my old pump to install on my new pump, I had to use an air hammer (and maybe a little heat from a torch???) to get it off. It's not something I could do on the water.