impeller change

[TimMcC]

Hi

How often should an impeller be changed ?. Would you change it based on the number of hours done or after a period of time or combination of both ?.

Thanks
Tim

[Locozodiac]

Originally Posted by TimMcC

Hi

How often should an impeller be changed ?. Would you change it based on the number of hours done or after a period of time or combination of both ?.

Thanks
Tim

Some engine manufacturers recommends a change evey 100/150 hours use, others yearly, but in reality will depend on the amount of water pressure seen on the exiting port, if it's poor or hesitates change, don't go longer, will overheat yor engine. Other issue will be a matter of cost, if the work is done in a shop, do it yourself if you were a mechanic. Impellers are cheap $ 15-30 depending on the model.

Happy Boating

[Ezgoing]

As mentioned wach for dropoff in water pressure. Ifboat is being used in sandy estury there will be more wear on the impellor.

After two three years all lower units should be dropped and the top of the drive shaft greased where it slots into the crankshaft. Failure to do this can result in the two bonding together with serious consequences. See other recent posts of difficulty of removing lower legs that have got siezed.

Best of luck.

rgds

[Locozodiac]

[QUOTE=Ezgoing;244949] As mentioned wach for dropoff in water pressure. If boat is being used in sandy estury there will be more wear on the impellor.

If normal engines are being used in sandy stuaries, muddy rivers & lakes the impeller and water pump case (cylinder) will wear out fast compared to sea use, in that case change for a chrome plated & reinforced impeller kit. Ask your store/dealer for them.

Happy Boating

[BogMonster]

Mine is 8 years old and on the original impeller, I know of another RIB here that is 1995 age and still on original impellers on both engines (Mariner 75 2/ IIRC). I got a lot of "attitude" from some folks here that mine was going to pack up as soon as I left the harbour because the impeller was knackered, well 2 years later it is still going, still has a strong telltale and no sign of problems. I probably ought to change it but if it ain't broke...!

Probably going to be a bugger to get off when I do need to though...

[Pete7]

Originally Posted by BogMonster

I probably ought to change

Thats a good idea, you wouldn't want any of the little bits of rubber breaking off and disappearing into the water galleries in the powerhead, that would a really nasty job stripping it down to find them.

Pete

[spartacus]

Mine is 8 years old and on the original impeller, I know of another RIB here that is 1995 age and still on original impellers on both engines (Mariner 75 2/ IIRC). I got a lot of "attitude" from some folks here that mine was going to pack up as soon as I left the harbour because the impeller was knackered, well 2 years later it is still going, still has a strong telltale and no sign of problems. I probably ought to change it but if it ain't broke...!

I change mine every year as a matter of course. An impeller only costs £15 and it's piece of mind when it's been done.

Sod's Law dictates that if it's going to fail - you'll probably be 5 miles offshore in a force 5/6 as it's getting dark.

Good opportunity to inspect the water pump, grease the drive-shaft, etc.

Use a rubber mallet to free lower end if it's refusing to budge.

[Richard B]

Experience has shown me that failure is gradual and results in low water pressure which can activate the overheat alarm at progressively lower speeds.

Last time I changed mine I did the base plate and housing along with the gasket as well as the impeller. The kit for my engine retails at around £95.

[Limey Linda]

Originally Posted by Richard B

Experience has shown me that failure is gradual and results in low water pressure which can activate the overheat alarm at progressively lower speeds.

Last time I changed mine I did the base plate and housing along with the gasket as well as the impeller. The kit for my engine retails at around £95.

This failure mode has been confirmed by my Merc. guy. The rubber blades of the impeller take a set over time and the problem may only show up at lower rpm. Every two years is suggested.

[Richard B]

Originally Posted by Limey Linda

The problem may only show up at lower rpm.

That's actually the opposite of what I experienced... first alarm happened a top speed, then progressively lower speeds until we limped home at little more than tickover. I reckon every two years more than often enough for a leisure outboard.

[BogMonster]

Originally Posted by spartacus

I change mine every year as a matter of course. An impeller only costs £15 and it's piece of mind when it's been done.

Sod's Law dictates that if it's going to fail - you'll probably be 5 miles offshore in a force 5/6 as it's getting dark.

Good opportunity to inspect the water pump, grease the drive-shaft, etc.

Use a rubber mallet to free lower end if it's refusing to budge.

Agreed - unfortunately this is not a great place to work outdoors (windy), it would probably be a much bigger job than I thought when I started it, and I don't have anywhere to put the thing under cover unless I take the motor off the boat and that opens up a whole new can of worms with not having done it before.

[Locozodiac]

One important issue that has not been given it's place and is associated with impeller change is how often should I clean my engine water passages ?

According to my particualr experience on engines, would state that even you flush well your engine after each use, with time, your water passages will beging to close/clog in thin layers of salt, like salt esclerosis. So if you want to keep your engine performing and above all cooling at it's best, remenber when it was new, you should al least disarn and clean your crak case, cylinder head, thermostat, exhaust cover, water passages at least every year for engines that are always at sea and not water flushed and 3 complete years for normal flushed engines.

Clean completeley all water passages with thinner, carb cleaner, etc and remove with a small screwdriver all salt incrustations, soft metal file related parts, put new gaskets and torque cylinder head and parts to appropriate factory specs. Clean thermostat well, check if works properly (opens/shuts) or replace if necesary. Change Impeller, polish pump case, grease drive shaft, take advantage of the disarmed engine to remove carbon buildup on pistons and cylinder head.

Had a engine overheat with a new impeller, the problem was that even the engine was appropriate flushed after every use, years of internal salt layers/incrustations/clogs were the failuire cause. That's why it is necesarry to flush engines on after use with at least a 10 minutes flush, to let time for the thermostat to open and flush correctly all internal engine water passages.

Any ideas are welcome to make users be aware of this issue.

Happy Boating

[Locozodiac]

Now that users have an idea on what time is best to change impellers & clean internal engine water passages, why not share a technical explanation with those boaters who haven't seen how an impeller looks, works and the procedure & tips to change them if sufficient skilled.

Although all impellers performs the same work, that is refrigerate/cool the engine down, all have different sizes, heights and rubber compounds, some are harder than others. The bigger the engine, the bigger the impeller. All rotate clockwise as the engine does, are located in the upper tail section inside a eliptical pump case, which is covered on top by a housing assembly, are moved by the drive shaft that moves the propeller and comes straight down from the piston crank shaft. Their delivering water pressure will depend on the engine rpm, lower-less, faster-more.

To replace when water pressure is low or as a peace of mind, once the leg is down, remove housing, place new impeller down through the drive shaft (put key to lock to shaft) until seats on top of the guide plate, oil, grease, soppy water the circunference of the pump case and impeller rubber blades. While pushing down the housing, keep turning the drive shaft clockwise untill the impeller is aligned inside the housing and well seated against plate, torque tight fastening screws to manufacturer specs. Grease impeller housing to avoid salt formations and whole drive shaft with a generous amount specially on cuts top shaft (where engine crank & shaft meets) to prevent seizing up with time. Try wheel bearing Lubrimatic marine salt water resistant grease if possible to get, has a trade secret long lasting formula.

If you are a peace of mind impeller changer, keep the old ones at hand, if your impeller has a straight border to border cut you can reverse them in a low pressure/out of stock emergency. Simply flip the impeller, grease and rotate it clowcksie untill corrected seated. Do so, only if the rubber blades are in perfect pumping condition, that is not heavily bent, nor rubber cracked. Will increase the water pressure, and last long. Check that all seal rubber water pipe connectors are ok, replace if necessary.

If not changing the pump case, a good suggestion would be to polish the internal cylinder, water moisten a used 3M green pad (the waffer type) and apply a generous amount of tooth paste, gently polish in both circle directions with finger untill the wall feels soft and even. This will make the new/reversed top blades of impeller last longer and pump better top pressure.

The photos will give a better visual idea of the related impeller issues & procedures treated on this review.

Happy Boating