Caterpillar 3126 sea water pumps - impellors, rebuild, or replace?

markrinker

markrinker

New Member
Jul 19, 2011
325
Lake Union - Seattle, WA
Boat Info
2000 410DA
Engines
Caterpillar 3126
Hello - I am the 'new' owner of a 2000 SeaRay 410 with ~530 hours.

When we bought the boat last August, the volume of water pumping from the port engine was noticeably less than at the starboard side at idle. Off idle, the volumes were similar, with no noticeable difference in operating temperatures - which I watched closely.

Now that the boat is laid up for the winter, my plan is to service both pumps. It appears from the fresh white paint on both units that they have never been touched, further evidenced by the spare Sherwood impellors found onboard...a project that never was completed.

Q1) Should I do just impellors - if both pumps appear dry with no drips or leaks from seals?

Q2) If you recommend a complete rebuild with impellors and seals, is this something that can be done by a first-timer, or should they be sent out to CAT or another facility?

Q3) Anyone carry a spare pump assembly as a spare, or are impellors good enough? We are on Lake Superior, and think I may know the answer to this question already...


Thanks in advance for your experienced replies!

Mark Rinker
Owner
MREBoatTransport.com
 
Congratulations on the new-to-you boat. You are going to love not only the 410DA, but the engines as well, once you get a grip on what is required to maintain them.

First, on a Sea Ray, you cannot always tell the volume of water pumping by the engine by just looking at the exhaust port. The reason is because you have an underwater exhaust outlet and the exhaust outlet you can see above the waterline is just an overflow . The overflow handles the excess water when the exhaust stream builds up some back pressure. The back pressure is always different between the port and stbd sides due to the plumbing differences in getting the exhaust from the engine to the exhaust outlet. Most Sea Ray DA’s with 3116/3126 Cat engines will show a little less water on the port side.

As far as impellers are concerned, they are usually good for about 200 hours or 2 years. If you know when yours were replaced, then you can decide if you need to service them. If you do not know, then you need to go ahead and replace the impellers so you will be working from a known reference point. If you let the impellers go too long, or thru too many winters, the blades begin to break off. When the blades start to break off, you can’t just replace the bad impeller, you have to go into the cooling system and find the broken pieces or they will clog up cooling passages. On 3126’s with OEM pumps, that usually means removing at least one heat exchanger end cap so you can reach inside and collect all the little blade pieces. It isn’t brain surgery, but isn’t much fun either, especially on the stbd engine.

If the pumps are not leaking, then don’t mess with the seals. These pumps can get Hope that helps……………..
expensive to rebuild and more times than not, you make the leak worse when you break one down. I have rebuilt mine twice, and every time you go into one, its life gets shorter. My first one was built at 400 hours; the rebuild lasted 225 hours and the second rebuild lasted 150 hours before leaking resumed. Cost is another factor. By the time you replace a shaft, seals, cam and wear plate, you will spend about $500 and a new pump is about $750. Sherwood makes the OEM pump for Caterpillar, so don’t go to Cat for the pump or impellers. A good source is Depco:

http://www.depcopump.com/marine.htm

The new pumps have some design changes and will last a lot longer than the OEM pump. My advice is not to rebuild the Cat pumps but to replace the entire pump with Sherwood aftermarket ones when it is time. Don’t replace the pumps unless one is leaking, then replace both at the same time.

So, if the pumps are not leaking just replace the impellers and do it now unless you have a service record that shows you it was done less than a year ago. Absent the service record proof, then replace the impellers now.

Tip: The Sherwood pump has an internal ¾”x16 tpi threaded bore. Get a 1-1/2” to 2” threaded bolt and screw it in the bore of the impeller and run it into the threads. The bolt will contact the end of the pump shaft and jack the impeller far enough out of the housing where you can grab it.

I wouldn’t carry a spare pump unless you are going to a far away land somewhere, for a couple of reasons. The pump is gear driven and the gear must be pressed off the tapered pump shaft or pulled with a big gear puller…….presses and big pullers are tools we don’t usually carry on a boat, so you won’t be able to chane it unless you buy another gear from Caterpillar and fit it to the extra pump. The other reason is that the Sherwood pump is pretty much bullet proof. You are not likely to have anything more go wrong than an impeller to fail. Impellers are an easy job on these engines, but even so, it isn’t something you really want to do in a busy channel or on a 5-6 ft swell off shore. Get in the habit of keeping up with your maintenance history and change the impellers ahead of time instead of waiting on them to quit pumping. Impeller kits are about $65, so stretching their life isn’t worth the risk of an emergency repair underway.

Hope that helps..........................
 
Wow! That sure does, Frank. As a longtime moderator on TheDieselPage.com's Duramax forum, I know how to spot the right answers from experienced posters.

I'll be following your advice, spot on.


Mark
 
Per Franks recommendation we replaced both pumps on our 3126's that are in oue 2001 420AC when one started leaking this summer. They were 10+ years old and we had replaced the impellers twice since we purchased the boat in 2007. Starboard change was very accessibe but the Port side is another story. Frank told us were to buy and they shipped them out the next day and greatly appreciate Frank's info. Yes we did repaint them white like everything else once they were installed and we made sure we had no leaks.
 
impellor1.jpgimpellor2.jpg

Well folks - here are what two ~530hr impellors look like. I feel blessed to have made the 600 mile journey across three Great Lakes last summer, without issue.

Since the pumps are dry and tight, we'll run them and keep an eye out for any future leaks. Observed engine temps last summer were consistant port to starboard, and never out of range.
 
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You do know how lucky you were making that trip don't you?

I think your maintaining normal temps with those impellers is pretty clear confirmation of my opinion that Cat over specifies cooling system capacity.
 
I concurr with Frank (what else is new, right!). I started overheating once on vacation and was about an hour from the next marina. I backed off a few hundred RPM's and made it to port without going over 205°. There were no vanes left on the impellor when I changed it...
 
YES!!! I am super lucky that one didn't grenade when I was 100 miles from nowhere! Having spares on the boat wasn't enough, after I learned how involved it is to access them - especially on the starboard side!!!

I got into some shallow sand/silt at a dockage one of the last days of the season. Pretty sure that put the finishing touches on already weak impellors, particularly on the port side.

I must be living right...LOL :)
 
markrinker said:
YES!!! I am super lucky that one didn't grenade when I was 100 miles from nowhere! Having spares on the boat wasn't enough, after I learned how involved it is to access them - especially on the starboard side!!!

I got into some shallow sand/silt at a dockage one of the last days of the season. Pretty sure that put the finishing touches on already weak impellors, particularly on the port side.

I must be living right...LOL :)
Click to expand...

When you feel as though you may have too close for comfort or actually felt the bottom, ALWAYS open your strainer to see if you have mud or seaweed! I carry a straightened coat hanger in the ER in case the seacock hose is clogged as well.
 
What is the deal with the o-rings for the cap over the impellar? The new o-ring was way too long. It was impossible to get it into the cavity and seat it before putting the cap on. We ended up cutting the O-ring and shortening it, inserting it into the cavity, and sealing the cut ends with a dab of silicone. Hope this lasts! On the second pump....we left the old O-ring in place!
 
Did you over-manipulate the o-ring, or was it not stored properly? They go out of shape very easy and I don't feel comfortable cutting one to make it shorter. I am very careful to keep them in the proper shape
 
The O-ring popped out when I removed the cap. I got a new O-ring when I bought the impellar. Neither one of the O-rings would go back in the groove without some end of it sticking out of the groove. Not sure how it is possible that even the original (and the new) o-rings both were to long to re seat properly
 
There were either 4 or 5 different Sherwood pumps used on various 3116/3126 engines. Each time they improved the pump, the housing and plate could have changed (I don't know the differences). Be sure you are getting replacement parts for the specific pumps on your engines. Unfortunately, getting pump parts from Caterpillar may not be as fool-proof and other Cat parts are because a previous owner, mechanic or boat yard may have replaced the pumps with a non-OEM version.
 
Got the boat back in the water last weekend. At startup, we idled the boat for about 10 minutes, observing no water leaks at the pumps (with new impellors installed). A 30 minute trip to heat the oil was next, followed by discovering that BOTH seals were now leaking a steady drip, drip, drip.

The mechanic that did the work was available, and he removed and resealed both plates, using one of the spare o-rings that was found on board in the CAT kit (green suitcase). The other he just repositioned.

So far so good. However my bet is I am visiting this again before the season is over. Those o-rings are worse than the ones on the Challeger solid booster rockets.
 
How do you change this impellor when the shaft with wires that goes in the engine is in the way ?

impeller4.jpg

I hesitate to unscrew the part with the wires and my other option seems to be removing the entire pump.
doesn't seems logical as those should be change often.
 
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On my 3126's, I was able to loosen a bolt on the bottom of that elbow and twist it 90°...I don't see that on yours though...I also had to remove a fuel line from my fuel cooler below the pump. That my be just to the right (out of your picture).

How long (calendar/hours) did you get out of that impeller?
 
is it the nut you see on the right?


At least 700 hours :( since i bought it in 2011 (not very proud of this)
 
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