Shelf life of impellers

[Project_Mayhem]

My boat came with a new raw water impeller in a box. Age is unknown. Does the rubber dry out over time?

Also, does the M25XP have a circulator impeller that needs to be replaced every so often?

 

[Davidasailor26]

Yes, unfortunately it does. I've had inconsistent experience with impellers, probably mostly due to their age after sitting on the shelf for a few years. Yanmar recommends replacement at 1000 hours or 4 years. I replaced one after about 5 years and it still looked fine so I saved it as a spare. The replacement, which had sat on a shelf for 2 years, only lasted another 13 months before losing a vane.

 

[Ralph Johnstone]

Also, does the M25XP have a circulator impeller that needs to be replaced every so often?

Sticking my neck waaaaaay out here but like a Yanmar, I would expect the impellor of the block circulator to be steel due to the toasty temperature of the antifreeze which rubber materials do not like.

 

[Project_Mayhem]

Thank you both.

@Ralph Johnstone I looked it up just after posting and discovered that you are correct

I will replace my raw water impeller AFTER winter layup. I've heard many technicians claim that the pink antifreeze destroys rubber impellers. Does anyone know of a source for impellers that's likely to rotate their inventory frequently?

 

[Ralph Johnstone]

Does the rubber dry out over time?

Same experience as @Davidasailor26 and installed a new Yanmar raw water rubber impellor after 10 years of use. It looked perfect when removed. Coated it with Meguiar's vinyl protector :

............ and sealed it in a zip lock baggy. Still looks great after 16 years and the new installed impellor still looks great is still going strong. I have to wonder if exposure to air (oxygen) is the culprit here.

 

[jssailem]

My boat came with a new raw water impeller in a box. Age is unknown. Does the rubber dry out over time?

From my experiential knowledge. Yes, rubber "dries out". However, these impellers are not made of "pure rubber". They are Polymer composites.

A Google search yielded this https://www.sciencedirect.com/science/article/pii/S2590123024000720. I was interested and it led me down a rabbit hole for 30 minutes.

An AI search provided me with this result in 1.2 seconds.

Material Degradation (Polymers/Composites)​

• Non-metallic impellers(e.g., PTFE, PVDF, polypropylene):
  • UV exposure (if stored near windows) → embrittlement.
  • Hydrolysis (moisture absorption) in humid environments → cracking.
  • Chemical outgassing or plasticizer leaching → dimensional changes.

My knowledge base was confirmed by data.

Finding a store with fresh products will be more difficult.

 

[BarryL]

Hello,

Let's discuss water pumps. You engine has two. One is the 'raw water' pump. This pump sucks up seawater (fresh water if you're in a river or lake, salt water if you're in an ocean, sound, bay, etc.). The other water is the 'coolant' pump. Just like a car or truck has a water pump to circulate coolant through the engine block, your Universal M25 has a water pump to circulate coolant through the engine block). Where the car has a radiator to cool the coolant, the boat has a heat exchanger. The automotive radiator is an 'air to water' heat exchanger, the marine heat exchanger is 'water to water' meaning that the seawater is used to cool the coolant. Note that the seawater and coolant never mix, they are kept separate inside the heat exchanger.

Note that your engine also has a thermostat (just like a car). When the coolant reaches a set temperature, the thermostat opens and allows the coolant to flow through the heat exchanger.

While the coolant pump can wear out and need replacement, that is pretty rare. Mote common is for the thermostat to fail closed. This will cause the engine to overheat. Signs of a bad coolant pump are leaks of coolant (not water) and an overheating engine.

Good luck,
Barry

 

[Richard19068]

Also, does the M25XP have a circulator impeller that needs to be replaced every so often?

@Ralph Johnstone I looked it up just after posting and discovered that you are correct
View attachment 235432

My understanding is a Universal M25XP is a Kubota D850. If that is correct you can get a whole new coolant pump from Kumar Bros for $32.89.

Kubota D850 Water Pump Parts for Sale - 15534-73030

Kumarbrosusa manufacturers and suppliers of kubota D850 watre pump tractor engine parts for sale with oem no. 15534-73030. Water Pump D850 used for kubota engine B1550D, B1550E, B1550HST-D, B1550HST-E, B6200D, B6200E, B6200HST-D, B6200HST-E, KH35 and many more.

www.kumarbrosusa.com

I used a Kumar coolant pump to replace the one on my M18 several years ago and it has worked just fine.

Of course you would want to verify the fit.