Impeller Problem
 

I burned out my starboard impeller yesterday. I have burned out my port impeller three times this year. :(

I think the problem occurs when I put the boat on my lift. When I raise the boat, the water drains out. When I lower the boat back into the water, there is still air in the lines. The boat sits high in the water and the seawater pump is above the water line.

The impellers run "dry" for a few seconds until the line is full of water. After a few times of this, the impellor fails.

To try and circumvent the problem, I plan to prime the water line by connecting a garden hose and "flushing" the engines after I lower the boat into the water and just before I start them.

As anyone else experienced this problem?

Do you think that Run Dry Impellers will fix my problem?

As mentioned in the GD, the run dry impellers do not flow as much water as the stock Mercury units. Hence, your running temps may be up 10-15 degrees.

Even though your outdrives drain when lifted, your plumbing from the transom to the SWP should not. Is this hose/plumbing level, or tilted fore or aft (when the boat is on your lift)?

Perhaps you can open the blue freeze plug drain on the SWP when you first lower the boat into the water. This ought to allow the air to be pushed/bled out, and water to push up from the transom assembly/outdrive.

Not sure why, but seems you must have some other kind of problem going on. My boat sits on a lift long periods of time and only have to change the impellers on a regular maintenance schedule. You might have to talk to someone that is more of a mechanic.

Also, have heard those "blue" run dry impellers don't flow the water, so not sure about them. In your case they may be the answer tho.

Good luck.

While the boat was sitting in the water, I disconnected the intake line from the seawater pump. Some water flowed in, but it was a weak stream. I thought I had a constriction in the line, but the problem has now occurred on both engines. I think that the boat sits high in the water and the seawater pumps are above (or right at) the water line.

I like to keep my gas tanks under half full so that it runs faster. Maybe I just need to keep my tanks full so that the boat sits lower! :D

are you putting any type of grease around the housing before you install the new impellers?

No

I've trailered my boats every weekend for years and have never had that problem. I'd say you do have a restriction, If I pull the water line off my seawater pump (no strainers) I get a fire plug worth of water coming in!!!!

You shouldn't use grease on the impeller install. When installing a new impeller, use liquid dishsoap as a lubricant..................

..........or in Clay's case, he could use some of the KY he's got on the boat:D:D

I've always heard to use SOME kind of lubricant. I wasn't necessarily referring to wheel bearing grease. :) Just something to coat the housing.

The grease is for installation and initial start up after a few minutes or hours its all gone. Have the motors been running hot? There must be something happening to cause that many failures. Did you replace the housings with the impellers?
Jim

Must be a obstruction in your pickup. Backflow your system with water. Lifts, putting the boat on a trailer and draining should not be causing impeller failure. It is running dry because it is not getting the proper flow. Check the hoses, make sure there are no kinks. Also check the valves and the pickups. Maybe there is some seaweed, or mud. Flush it. Should get 2 seasons out of an impeller.

Clay,

I keep my Bullet on a lift and I have not had that problem. Once the boat is lowered in the water, the seawater pump is close to water level anyway (very little head difference). I would check where the water hose connects to the transom addembly (behind the angle fitting). I had to replace both my transom assemblies due to heavy corrosion that collapsed the water line that runs through the assembly. Like someone else said, water should come out like a fire hose when disconnected from the pump.

That's where I was leaning. When I did the repower on my old Formula I had the same issue. The hose that runs from the outdrive to the transom assembly can get crushed by corrosion of the aluminum around it.

I had a similar problem last year with one of my pumps.
Turns out that after sitting on the trailer for a week, pump would loose its prime due to the fact that the pump housing was scored and would let it bleed off.
I changed quite a few impellers before I figured out what was causing the problem.
Changed the housing and problem is cured:D

I had an issue with my pump not priming (trailered boat) and it was a worn housing. Was not really scored so not super obvious the housing was bad, but once I had a new one next to it was for sure. Replaced and problem solved.

OK. I will replace the housing and see if that corrects the problem! :)

What's your water psi when the impellers are new? Before you spending $$$ on a housing check to see if you have a restriction at the gimbal housing as doraymond said. Very common problem and poor design on mercs behalf. Seriously doubt if its your housing. As others posted water should be exiting like a fire hose when you disconnected it from the pump.

I agree:cool-smiley-011:

I have seen many times over that the build up in the transom is the problem. If you can get to the fitting that bolts to the transom connecting the reinforced hose, you will probably see that the impeller is trying to pull through a straw sized hole. I am suprised that you have not seen high temps.

Most likely, the electric condom dispenser you installed crimped your outside water supply.

No, he's using too much water to fill the hot tub he mounted in the cabin for parties, which leaves very little water available for the motors.

Priorities ! :D

Could be.

You may also have too much water pressure while running on plane. This would cause ecessive wear and tear on the impellers as well. Before changing the housing, check your water pressure. It may be too low or too high.

OK. How do I lower or raise the water pressure while running?

Clay, its getting hard to tell who's trying to help and who's busting your ball's. "Don't spend the $$$ on a new housing. Maybe you have too much pressure". Good luck with all the help your getting.
Jim

Start from the top on down

Replace the boat and the problem will most likley go away

:)

seriously

I had 3 different boats on my lift over the years ( 38 Scarab, 43 Black Thunder, 38 Cigarette) and kept it High and dry with not even the drives in the water and never had this issues

You have something else going on

Leaving it high and dry should not make a difference

Same here Clay. I keep mine on a lift and sometimes don't run it for extended periods. Never had an issue with impellers. Primes right up as soon as I crank it and I have a fairly high X-dimension. It will be interesting to hear the actual problem once you find it.

Did you go talk to Grant and Clyde? What do they say?

Keeping the boat on a lift doesn't creat any issues with getting water on a good set-up. Have you dug out all of the impeller peices in the coolers?? Are you sure?? Backflow the system from the T-Stat housing to the pump. Pull the hose leading into the cooler and check for any remnants of old impellers. If all checks out OK - then pull the hose nipple from the transom assembly (Inside the boat) and see if you have a blockage there. I've done 7 boats this year with the same issue - all around the same model as yours. I know your in fresh water - but you've run the boat in salt before -yes? If you have ANY problems with getting the two bolts out holding the fitting on - stop there. Make sure you don't break them off in the gimbal housing cause it's a pain to drill and tap with the motor in. And if all in all you can't figure it out - make a trip down to Houston and I'll give you a hand - then we'll go run the chit out of the NorTech or Hemi boat - whoever is ready to go out....... LOL!!!

how deep is the water under your boat? when you put it in the water you might be in shallow water and sucking up sand or when you pull the boat off and start moving it may be shallow check it out Greg

No sand anywhere near his slip. Rocks...........and BIGGER rocks!

I pulled the starboard impeller. It's fine. The hoses were full of water. I now suspect the thermostat.

I checked the water level. The seawater pumps are defintely below the water level. However, the water does not "rush" in when I disconnect the inlet hoses.

I may have more than one problem.

I'm still working in it...

? for ya. Before you had this problem what were the water temps and psi at that point compared to now?

The engine temps run steady at 150. The PSI varies depending on the engine RPMS.

I have the "original" thermostats that came with the boat in 2006, so I don't know how old they are. I think that the starboard thermostat was stickng and caused the engine to get hot. I shut it down at 180.

This has not been a major problem, just an annoyance. :rolleyes:

I would compare the flow of water from each side of the sea water intake hose. While on the trailer & the boat submerged pull each hose off individually & take note of the differerance. More than likely the side that is normal will fire hose psi just as if you had a hole in the boat. And/or remove the hose fitting at the the gimbal (boat out of the water) and compare the differerance. If that hose retainer is not perfectly round you have found your problem. If they both are the same try backwashing the problem side. You may have a clog from the drive pickup to the gimbal. Or a clog in the oil cooler. Its a process of elimination.

well... I backflushed everything I could find, reconnected all the lines, and took the boat for a run.

Everything is working perfectly now. :D

Thanks for all your input! :)

Clay if you want to try a set of Run Dry impellers let me know I have 2 w/ less than 10hrs on them.

Michael