How long will a impeller last with the volvo grease

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asteven221

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Launch the boat yesterday and the engine started first time, but no water was came out the exhaust.

I had replaced the impeller last week along with cleaning the strainer and fitting a nice new hose between the raw water pump and the strainer.

The issue was resolved by manually filling up the quite large water strainer housing, so all seems fine now.

It got me thinking. How long can the engine be run dry without trashing the impeller? Assume that the whole sachet of grease provided with the impeller has been used to lubricate the blades and the brass surface within the pump.

Just curious.
 
I don't know but as soon as you hear an overheat alarm or don't see water coming out the back kill the engine straight away (but you already know this) or you'll trash a lot more than the impeller...
 
I don't know how exactly how long, but I do know it depends on impeller material. Some impellers are made with nitrile (I bought one by mistake), and while this is better for being able to cope with fuel and other contaminants (e.g. for bilge pump use) it is said to be less able to cope with running dry.

It also apparently depends on the pumps housing. Speed-Seal (now sadly closed for business) used to market the Speed-Seal Life, which puts a PTFE disc between the impeller and the cover. This is said to extend dry-running life significantly, supported by a series of tests. With this arrangement it said on a Yanmar it was tested by 10 runs of 10 minutes dry without failure. This implies that it likely wouldn't have so lasted with a conventional arrangement, (I haven't reviewed all the details but they are still on the Speed-Seal website at http://www.speedseal.com/SpeedsealLife/LifeTestResults.html ) As others have previously pointed out, such a cover does nothing for the back end of the impeller, or the blade tips.

I would guess that an impeller would last longer dry in a worn pump (but, of course, will not pump so much water when operating normally).

By the way, I was unaware until relatively recently of the idea of putting grease on an impeller when installing. I had always previously only wetted an impeller with water on installation, to lubricate it and help it seal to prime itself. This seemed to be effective, and I am not aware of any adverse effect. My last few impellers (different engine) have come with a little sachet of grease, and I have used it.
 
I once forgot to open the seacock before starting up, and also forgot the regular look over the stern to check for water, excuse it was dark and 04-00hrs!! - anyway we departed the marina and pottered down river for at least a mile before the alarm sounded. I immediately opened the seacock and water flowed well. I had a think and decided to carry on, but check the impeller when we arrived at our destination. It was absolutely fine and was changed the following winter as routine.
 
Quandary said:
I did not know you should use grease, I have always used glycerine, has that advice changed?
Click to expand...

Never used anything ... and still same impellor in there ......

I've run it dry when launching before hitting water ... partly dry when feeding A/F through it ...

Its well over 15yrs old that I know ... and I was told it was same one previous owner had in it ... Perkins 4-107.

This was taken other day before putting the A/F through ... (smoke is because engine hadn't been run for quite a while and was still cold .... ) but that water is at about 25% throttle ... at full - its a bloody blaster !!


 
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Last season I forget to open the sea-cock after working on the engine (Volvo 2003) and replacing the waterpump seals and impeller, and ran it for a very short time - 1-2 minutes at the most; certainly a short enough period that I never thought that the impeller would be damaged. I then discovered that little or no water was coming out of the exhaust. Having discounted the possibility of the impeller being damaged, I jumped through all sorts of hoops, including cleaning out the exhaust elbow, testing the thermostat etc. At last I took the cover off the water pump (which I should have done first!) and discovered that my impeller was in about 5 pieces. It had been greased with the grease supplied in the impeller replacement kit.

So, the answer is, check the impeller first! They don't last long if run dry, even with the grease, which is only there to ease getting the impeller in.
 
AntarcticPilot said:
Last season I forget to open the sea-cock after working on the engine (Volvo 2003) and replacing the waterpump seals and impeller, and ran it for a very short time - 1-2 minutes at the most; certainly a short enough period that I never thought that the impeller would be damaged. I then discovered that little or no water was coming out of the exhaust. Having discounted the possibility of the impeller being damaged, I jumped through all sorts of hoops, including cleaning out the exhaust elbow, testing the thermostat etc. At last I took the cover off the water pump (which I should have done first!) and discovered that my impeller was in about 5 pieces. It had been greased with the grease supplied in the impeller replacement kit.

So, the answer is, check the impeller first! They don't last long if run dry, even with the grease, which is only there to ease getting the impeller in.
Click to expand...
I have to say my experience is closer to Leighb's than yours. Following a couple of occasions meting out impeller abuse (unintentionally, though not to the the point of overheat alarm; on my boat the booming exhaust is the giveaway) the item survives unscathed after 5 years / 1700hrs.
 
Quiddle said:
I have to say my experience is closer to Leighb's than yours. Following a couple of occasions meting out impeller abuse (unintentionally, though not to the the point of overheat alarm; on my boat the booming exhaust is the giveaway) the item survives unscathed after 5 years / 1700hrs.
Click to expand...

Having an unsilenced engine - I soon know if the water is not going through ... its loud.

I can also hear the water gushing out when its working.

Sometimes I think about adding silencer but the that means all sorts of mods to accommodate etc. and TBH .. with the long exhaust pipe and large water flow - its no more than most other boats I hear.
 
If I close the seacock before the tide goes out it traps water in the piping and lubricates the pump on first start if forget
to open seacock.
 
Some boats seem to get through a few impellors every year, others seem to last forever. I wonder why that is though..
I ran my engine in a boatyard with hose pipe . after 40 mins or running i went to put all the pipes back where they should be and discovered i had actually bypassed the sea water pump all together.( it was still rotating)
Can only assume it had some water in there as when i took the cover off it looked as good as the day it was fitted new, some 33 years previous ! Its now 37 yrs and the jabsco rubber impellor is still looking great.
My seawater pump is stainless with 2 greasers on it. One does the longer shaft on the pulley wheel end and the other does both end bearing and impellor itself.
I used to take it out every year to inspect but getting bored with that now.
The replacement spare impellor has been knocking around for so long that it has probably hardened and useless?
So how long will an impellor last ? God only knows !
 
Always good to check the impeller after a "dry run", for no apparent reason mine failed just off Dodman Point last summer. No water, checked the system all worked, but still no water. The rubber had parted from the collar in the middle. That's never happened before.
 
You say the grease would be flushed out in minutes, i can understand that, but when i take my cover off there is a good smear of grease, especially between the impellor and end plate !
 
So I guess the answer to my post is that nobody knows! Fair enough neither do I.

Incidentally the grease I referred to is the sachet of "grease" (which isn't actually grease) supplied by Volvo when you buy an original Volvo impeller kit.

I always thought it was supplied to deal with the likely possibility, that on first starting the engine there could be a short period when the pump runs a bit too dry. I am not so sure it's supplied to make it easier to install the impeller, as the minute you cover the impeller with the stuff it becomes like a bar of wet soap! From the perspective it would be easier to install it (at least on my D2-55) without the stuff.
 
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