My raw water pump was pissin' me off!

[boomerang]

A while back I fired up our trusty Detroits after replacing the oil cooler line fitting on the port engine to (A) check to verify my repair was ok & (B) just to hear the happy growel of our trusty Detroits. They had not been started since we arrived at our wintering location in Georgetown, SC last November. On the trip down, everything was damn near as good as we could've asked for (with the exception of the above mentioned leaky fitting). The first cold start they both came to life with no coaxing at all...they truly are some good running 4-53's...where I did my customary walk to the transom to check for exhaust water flow. The starboard was sounding a bit throaty because there was no water coming out. S#!t. I shut them down and check the seacocks. They were both open. OK, maybe the impeller lost some blades, even though I replaced both of them prior to our departure last fall. I pulled the plate off and water poured out everywhere. Huh. I thought maybe something happened to the seacock not allowing full flow when I reopened them for the season so I pulled the heavy hose off of the intake side of the pump and held it down below the water line where I verified plenty of flow. OK...? I reassembled everything and restarted. The housing felt cold so I went beck to the exhaust where I saw lots of cooling water! I proclaimed the lemon squeezed even though I had no idea why I had an issue or what caused it in the first place.
Fast forward a week or 2 and I started the engines in preparation and to check things for a quick haul next door to check for a clicking noise near the port wheel we were hearing ever since having to lean on the throttles/clutches VERY aggressively waiting for the bridge in Wrightsville Beach in gale-strength winds on Thanksgiving Day (that issue will be in another thread some other time). Anyway...after starting the engines, the water flow looked good and I went to the helm and increased the RPM's a little to expedite warming things up and again ,just to hear them. But wait. Damn that starboard engine sounds dry! I slowed them down ,went aft and found no water coming out of the pipe again! WTF! I went through the whole routine again, checked the impeller, checked the gasket, checked the seacock water intake flow...all looked good. I restarted and what the heck? I had water flow...until I revved the engine. That's when it would quit, after increasing RPM's , where I couldn't get it back. At least I was getting somewhere even though I didn't know where I was going.
I finally decided to pull the impeller to examine it more closely. It looked good. No broken or cracked blades. What the heck. Out of desperation and grasping for straws,I pulled out my pump spares. I had a pump shaft so I stuck the impeller on it and twisted. Damn if it didn't easily spin on the hub! After it cooled a bit, it was all I could do to spin it on the hub. Come to find out, the pump would pump upon starting and continue to pump until a little more force was exerted on the blaces by increasing the RPM's/flow, where it would heat up on the hub and start spinning. I replaced the impeller and it looks like we're all good for the '25 season.
Attached is a picture of the Chinese-manufactured impeller and pump. They've performed ok except for this 1 glitch and hopefully the only glitch. Looking at the impeller, you can imagine why it didn't look like a smoking gun and I chased my tail trying to fix the problem for a while.

 

[psneeld]

The old "could not duplicate" on the maintenance signoffs to the point where you want to punch someone.

I just had a similar situation involving troubleshooting with my RV generator, Started, but stopped in a minute. Gettin' ready for an upcoming 3 week trip... of course I dove into troubleshooting. In a minute or two I figured it was fuel related.... disassembled and tested everything back to the fuel feed, Ordered a new pump just in case as It would pump one minute but not sure steady enough. A tiny voice in the back f my head was saying it might be a problem with the fuel line.... but an even tinier voice was saying...don't forget the fuel level because many RV stop feeding fuel to the Genset at 1/4 main fuel tank so you don't run it dry.

Well I traced lines, tested components, etc, etc spending a half day disassembling and reassembling everything. Well now the Florida temperature has risen quite a bit (probably expanding my fuel supply by just enough and not the Genset runs fine for 5 minutes or so. Now pretty happy so I continued my other tasks long forgetting that very important tiny voice's info.....

.....until........ the next day when I started up the RV to drive it a bit, top off gas and get propane.

Sure enough...gas gauge shows exactly a 1/4 tank. That tiny voice is now giggling and telling me never to ignore it again when troubleshooting as it may just save hours of labor.

Sorry Shawn, not implying anything more than when something is "not able to duplicate"..... it often is not one of the normal troubleshooting items we all seem to jump into. Once upon a time I had an impeller that for whatever reason would do the same thing. It was back when outboard props started to come with the sacrificial hub and that out of the box test on the impeller showed it would spin the center but not the vanes to pump. A big "ahah" moment which I bet you had too.

I bet from now on your tiny voice now has some very valuable advice in your troubleshooting water pump issues.

Safe travels North!

 

[Greg QS]

I had this problem on a genset once and once on Detroit's also. I kept loosing the bond on the impeller to the brass. Thought the same thing a crappy impeller. But it kept happening no matter what impeller brand I used. I finally figured out I had a partial clog in the exhaust elbow. To much back pressure. On the genset the elbow was replaced never reoccurred. On the Detroit's the Shower head outlets in the exhaust tube were clogging with caked in salt. Over the years with shut downs the residual salt water left salt behind. I got in there with a Dremel and cleared the salt. I set up a fresh water flus system and it Never re occurred. I would take off the exhaust hose at the shower head and inspect it for clogging.

 

[tiltrider1]

I bought a cheap impeller for my genset once. Worked great for a year and then it started spinning on the hub. Took a minute to diagnose the issue.

 

[Lepke]

I got spare salt water pumps For my Detroits on ebay and rebuilt them. Quality parts are available, Depco and other places.

 

[boomerang]

I got spare salt water pumps For my Detroits on ebay and rebuilt them. Quality parts are available, Depco and other places.

I'll be honest. I have a couple of minor kits onboard for the genuine Detroit pumps. This past fall, the starboard pump had a drip coming from a leaking seal. I removed the pump and replaced the seal, reinstalled it and it still leaked. It wasn't obvious to me how in the heck the pump came apart so I could inspect the shaft (believe me, I tried). I finally took the quitters route and put a whole new Chinese pump on and kept the Detroit pump as a leaky spare. I'd love to get the genuine one rebuilt but getting the shaft out seems to be beyond my megar skillset.

 

[Nautica]

Yep!, this is almost a common problem. Had it happen a number of times...

 

[O C Diver]

In all fairness, my Onan generator, with the Kubota engine, has a Sherwood raw water pump. Between spun hubs and broken blades, I couldn't get much over 100 hours between impellers. Didn't seem to matter whether Sherwood packaged or Onan part. Then something changed and new packaging. No more failures.

In general, when it comes to raw water pumps, I buy OEM pumps and OEM pump parts.

The original pump on my John Deere ran 5,000 hours, other than impellers. I looked at rebuilding the pump as part of my 5,000 hour maintenance. Replacing the impeller, bearings, seals, compression fork, front bearing plate, and rear cover were 75% of the current cost of a new pump. So I installed the one in spares, and bought a new one.

Ted

 

[boomerang]

The OE Detroit pumps are well over $2k last time I looked and a Chinese knock-off was less than $500. The port Chinese pump has several seasons on it, the starboard pump I replaced before we left to head South and the impeller failed after around 50 hours. We don't cross oceans and our cruising is inland/ near-coastal so I'll probably keep using the cheesy pumps and keep a closer eye on them while underway.