True story. When I purchased Midnight Sun I changed everything. The impellers on both engines were originals, 10 years old, 1,000hrs on the clock! I was shocked to see they looked new with no visible wear and were very soft and flexible like rubber should be. By no means is this normal however Volvo must know something compared to my previous experiences with Mercruiser or the previous owner was just very lucky. My previous routine for preventative maintenance on my Mercruiser equipped boats was to change every 5 years to be on the safe side which worked wonderfully in my boating area.
This is a highly debated subject as some change every year, others 2 years, others remove them for winter layup. Pristine waters vs salt water vs sandy water vs murky waters all contribute to longevity. Never and I mean never start and engine even for a a very short period without water, you will either compromise or destroy the impeller in less than a couple of minutes.
Cheers, Hans
2007 Carver 41 CMY
Twin Volvo D6-370's
Montreal, Canada Midnight Sun I Photos
The reason its easy for me on this boat with the new mercs is that I always loosen the belt tensioner off....I have done that with the boats and cars over the years in storage and this merc is real easy....no big screw drivers or pry bars to get it tight again... Then you can just reach down and turn the pump pulley easily after doing that. I know , most people won't be going to these lengths......it's a bit anal...
I would crank the engine over ( 90 degrees) with a bar, but the crank nut is very small 5/8" on these GM's and easy to break if you are not very careful. ...also never liked the idea of the engines sitting in the same spot....good idea before spring startup to get the cam in a different position to unstick valves if it was not winterized well.
Last edited by bud37 on May 22nd, 2020, 7:30 pm, edited 1 time in total.
I pump the engines under their own power. Not a good idea to use the crank nut these days. Pretty common to do with beefier older builds but not any more IMO.
I actually changed the impellers today. I do about 100 hours a year on my gas Crusaders. Prior to sealing them back up, I spun them by hand to see what would happen. They adjusted to the right form with the firs5 spin.
I was shocked to see they looked new with no visible wear and were very soft and flexible like rubber should be. By no means is this normal however Volvo must know something compared to my previous experiences with Mercruiser or the previous owner was just very lucky. My previous routine for preventative maintenance on my Mercruiser equipped boats was to change every 5 years to be on the safe side which worked wonderfully in my boating area. 
Then you can just reach down and turn the pump pulley easily after doing that. I know , most people won't be going to these lengths......it's a bit anal... 
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