Alarm Bells lead to Impeller Replacement
My wife and I set off for a weekend cruise aboard our Sabreline 36 powerboat. Our eldest son and his girlfriend had to work during the day but planned to meet up with us that evening. We left Everett, Washington and powered past Hat Island into the Saratoga Passage, destination Roche Harbor. The boat seemed to be running fine when about an hour into the cruise the temperature on the starboard engine came up and an alarm sounded. I stopped the boat, shut off the engine, and began to investigate, leaving the boat drifting with the port engine idling in neutral since we were in a two-mile wide, mostly calm channel.
Troubleshooting on the fly
After entering the engine room, I noticed some coolant had overflowed but mostly was contained by an external overflow tank I previously installed. I checked the oil which looked fine and had no sign of contamination. I closed the seacock to the raw water on that engine and carefully worked open the Groco sea strainer looking for a “bag-fish” or some other blockage. There were a few pieces of seaweed in the strainer and a little bit of what looked like algae buildup, nothing that seemed serious. I cleaned the strainer and the bowl and reassembled it. After the engine had cooled off enough, I was able to open the coolant chamber. It was a little low and slightly dirty, so I added coolant, but it did not take much.
I restarted the starboard engine, and it sounded fine and did not alarm when idling in neutral, so I shut down the port engine and inspected and cleaned the sea strainer on that side too before restarting. Unsure of the issue I put both engines in gear and slowly brought them up to a slow cruising speed. Watching the gauges, the starboard engine started heating up within a few minutes and the alarm sounded so I shut her down again. We knew without addressing the issue we couldn’t go all the way to the San Juans and debated running on one engine to Penn Cove, but it would be two plus hours on one engine and then we would need to limp all the way back. In the interest of prudence and to keep the boat from further harm we decided to head back to our home slip on one engine and come up with a different weekend plan.
Arnie’s checklist after high temp alarm sounds.
- Shut off the engine
- Note coolant overflow (without opening the hot cap)
- Check oil for cross contamination
- Close seacock on raw water intake on the stopped engine
- Open sea strainer, check for blockage, clean and put back together
- Remember to open sea cock back up
- Once engine has sufficiently cooled carefully open pressure cap and check coolant level
- Start engine and check for water flow in exhaust and watch gauges
The Diagnosis
I didn’t want to spend half the weekend in the bilge attempting a repair and then risk going out with everyone aboard and possibly having to turn back again so we shifted our weekend plan to the more land-based activity of wine tasting in Walla Walla. The boat was safe in her slip, and the repair could wait.
I did make some calls to some knowledgeable boaters I know and everyone I talked to said “impeller.” It made sense and I should have known better but even after many years of boating we all still have lessons to learn. When I bought my boat four years ago the survey said it needed water pumps. Not knowing the boat at the time, I had a mechanic install new water pumps. He never told me how long the pumps would last nor suggest that I get spare impellers and replace them every few years and I never asked. My fault, not his, but some guidance would have been nice. Several knowledgeable boaters and a mechanic I called after the overheat advised me that replacing impellers every two years is a good idea. I had also noticed that the exhaust water output on the port engine (the good one) had recently slowed down. It now all made sense, that engine needed a new impeller too.
Replacing the Impeller
The water pumps that had been installed on my Caterpillar 3126 engines are Sherwood 1710 C’s not OEM pumps. I luckily found the appropriate impeller replacement kit for them which set me back $80 (each) at the local chandlery, but hey they had them in stock. On my boat the engines are very tightly packed as originally the boat had 250HP Detroit Diesels and the 300HP Cats were added later as replacements. The water pump is on the inboard side of the starboard engine meaning it is reasonably accessible. This would allow me to figure out and repair the down engine first before attempting the much more logistically challenging port engine which I suspect also needed impeller replacement.
I shut the seacock and slowly unscrewed a plug in the water pump to drain it, placing a bowl beneath to catch the seawater, so it wouldn’t dump into the engine pan. I then removed the three bolts that covered the impellor compartment and put the cover-plate, gasket, bolts, and lock washers in a cup for safe keeping. I was kind of expecting the impeller to be torn apart but it wasn’t, although it did look a bit worn compared to the new one. There is a little cap that covers the spindle hole on the impeller, and I removed that which reveals a threaded metal piece in the center of the impeller.
I was told not to scratch the inside of the impeller housing, which is brass, so I carefully put a needle nosed vice grip on the rubber impeller vane on one side and a needle nosed pliers on the other and tried to pull out the old impeller wiggling it back and forth in the tight space. It barely budged so I bumped the engine to turn the impeller. This means turning over the engine slightly but there is no raw water, so you really don’t want to run it. The bumping seemed to help a little but no matter how hard I carefully pried, the impeller didn’t want to come out. I used a board to wedge a screwdriver so I could pry on the central metal hub but even that didn’t work. I lubed up the spindle with Aerokroil (now Kroil) which is expensive bust off stuff that comes in an orange can that is safe to use on rubber but that didn’t seem to help either.
Impeller Puller
Searching online for solutions that would get the impeller out but keep me from damaging the pump, I found a Sherwood SH25105. This puller has the unique thread 3/4” with 16mm that is in the center of the impeller. The impeller doesn’t thread onto the spindle, it slides on and is aligned by a key. The threads allow the puller to attach to the impeller and then you can either pull it out or thread it in till it pressures against the spindle forcing the impeller out. There are a number of other impeller pullers on the market, some very expensive but since this one seemed intended for my impeller and was only $25 I thought I would try it.
The puller arrived and it threaded onto the new impeller relatively easily when lined up perfectly, but the plastic threads seemed like they could be easily stripped if cross threaded into the metal which concerned me. I pictured trying to twist this handle on with one hand and no clear sightline on the port engine but first had to try it on the accessible starboard side. Unfortunately, when I brought it down into the engine room there wasn’t enough room to thread the puller onto the water pump without removing the pump or other engine components. I thought about cutting it down, but we would probably have to cut off part of the handle too to make it work, and there still was the plastic threads that I did not really trust.
Home Made Puller
It seemed to me that was needed was a 3” – 4” bolt that had the correct thread. With metal to metal the chance of cross threading was less and the bolt could be turned to slowly pressure the impellor out or levered to do the same. The problem was that no local chandlery, hardware, or fastener store had the 3/4” – 16mm large but fine threaded bolt. As luck would have it, a friend was telling a fellow boater about our dilemma, and he had experienced a similar issue. His solution was to buy a threaded bar, cut a piece off, and tighten two nuts together on it so it could be turned. The bar was the right size and thread and we only needed a few inches, so he let us cut a piece off of it.
I threaded our homemade impeller puller into the old impeller still snuggly jammed in the water pump housing and began to turn it with a 1-1/8” wrench. As it pushed against the spindle each turn pushed the impeller a little further out of the housing. It was in there pretty tight because I couldn’t pull it out by hand until two thirds of it was sticking out. Upon removal the key fell into the pump basin but luckily not into one of the ports.
Impeller Installation
I wiped out the pump housing which seemed to be in good condition and bumped the engine until the keyway was pointing up so I could place the new key in without it falling. Then I took the new impeller and carefully secured two plastic cable ties around a half inch from each end of the impeller to hold the spines in. With the new key resting in the keyway, I worked the impeller into the housing and then cut the first wire tie. Now I turned the notch to align to the key and pressured the impeller in until it snugged over the spindle and locked the key in place. Then I removed the other hose clamp and pressured the impeller fully in. Next, I slightly greased the cover plate, placed the O ring in its channel, and carefully bolted the cover plate back on. I opened and shut the seacock slightly to make sure water poured out the still open water outlet hole so I knew it would get to the pump before I dogged down the plug.
After opening the seacock fully, I started the engine and watched the gauges. Idling in the slip wasn’t a very good test and I did crank the RPM up a few times and watch for water coming out the exhaust which for some reason never has been very much on this engine. I couldn’t get her to overheat so this impeller replacement is likely what was needed. I will have to do the other side and then take her for a run to really tell.
This project wasn’t as easy as it sounds in the slightly confined space but was a good practice run for the extremely confined port side impeller replacement that I need to do next. My weekend may have changed but we can go again once I am sure the boat is dialed in. Now I know how to change the impeller and have the right tool to do it with. I plan to carry spares on board from now on and change the impellers every two years so I can prevent another problem like this. I wonder if the water pumps were really bad when I bought the boat or if they just needed new impellers? I suspect the latter but will never know for sure. If you have a boat like mine, learn how to change your impellers or have someone do it for you. Noone likes to hear alarm bells aboard on their vacation.
