Impeller, what are signs it needs replaced?

[IGeeky1]

Hi everyone, I've got a pretty new sterndrive and it probably only has 10 hours on it as this point. I see where people replace the impeller every year and every other etc. I understand the wisdom of preventative maintenance.

My question is, if the impeller is in NEED of being replaced what will be the symptoms?

Thanks,

Mark

Merc 3.0 140 w/alpha 1 on a 1989 sylvan skipper 21

 

[ktbarrentine]

The "basic" symptom is if the engine water temp gauge starts to rise significantly above the "norm" you are used to, particularly when operating at low speeds/idle/no wake zone when the impeller is turning slower. When really going, it shows higher temps no matter what. But (caveat), you can see overheat for other reasons, like debris in the cooling circuit, plastic bag over the intake screens, stuck thermostat, etc. Thumb rule is that checking the impeller is the first thing to do on any overheat.
I am one of the ones that change the impeller ever other season no matter what the hours are, because the impeller can take a "set" on the vanes over that amount of time. It's a good time to take the drive off and do all the other required checks and maintenance too.
I am sure you will get alot of other input and advice. Best of luck and happy boating!

 

[achris]

With the early style (short stiff vanes) impeller t does need to be replaced at an interval no greater than 2 years, but annual is best. Usually by the time you get the drive pulled apart and the impeller housing off, what with using new base plate gaskets anyway, you might as well replace it anyway. Peace of mind and cheap insurance.

Chris.....

 

[alldodge]

Hi everyone, I've got a pretty new sterndrive and it probably only has 10 hours on it as this point. I see where people replace the impeller every year and every other etc. I understand the wisdom of preventative maintenance.

My question is, if the impeller is in NEED of being replaced what will be the symptoms?

Thanks,

Mark

Merc 3.0 140 w/alpha 1 on a 1989 sylvan skipper 21

Agree with above and will add; With an alpha 1, replace the impeller every 2 years unless something tells you to do it sooner. The impeller kit and lube is cheap compared to replacing an engine, head or other items.

 

[thumpar]

I replaced my Alpha impeller every 2 years. Sometimes they don't even show any symptoms and just detonate leaving you stranded.

 

[achris]

More often the rubber impeller bonding to the hub (sometimes brass, sometimes fibre) will let go... When that happens, INSTANT overheat.... Then you're up for replacing the impeller, but also the pump housing and the water pocket cover, because all that uncooled exhaust gas getting in the exhaust cavity in the drive has a fun time in there.... And then you don't have a fun time fixing it all.... No, a new impeller every 2 years is way easier....

 

[GA_Boater]

If you don't know when it was replaced, even a newish lower unit with probably 10 hours on it, replace it. Then you go with the annual or biannual maintenance replacement. An impeller sitting in the housing and pretty much unused isn't good for it. It hardens and takes a set, so it's worse than running the boat. My opinion.

 

[achris]

.... An impeller sitting in the housing and pretty much unused isn't good for it. It hardens and takes a set, so it's worse than running the boat. My opinion.

Completely correct. I have serviced many boats that are 'Used once a year at Christmas' and many that belong to commercial fishing companies... Which ones do you think are in the best condition? The ones used every day or the ones that are put away and not touched for 364 days a year? If you think not using an engine helps keep it in good condition, think again... Those once a year engines are a nightmare. The impeller MUST be replaced every service, and getting the bolts out is freaky difficult, all corroded and seized solid... My favourite saying in this situation is.... "It's not using a boat that kills it, it's not using a boat that kills it"....