How hard is it to change the impeller on the 496 mag ho, bought a 05 heat in late oct and when we fired it up during inspection it took a few for the water to start coming out of the exhaust, the previuos owner had to go into the engine bay and hand pump the rubber hose. The boat was fully winterized.

Not too bad if you have some room to work with. Remove belt, 3 bolts to remove pulley bracket on front of motor, remove clamps on inlet and outlet hoses, pull water hoses off of pump, disconnect quick drain air tubes and slide the pump off. With the pump out, remove the bracket and cover screws and pull off back cover. Replace impeller and reverse install.

First time I did it took about an hour after that I can swap one in about 20 mins.

I did it on my heat last season. I think there is plenty of room, at least compared to previous boats. Like techman said, remove the pump as an assy, then take the housing apart on the bench. My housing was very worn, ended up installing a Hardin stainless pump

Actual replacement of the impeller is easy as pie.
Getting the pump off of the boat is usually the hardest part.

As mentioned, it's all about how much room you have to work. There are boats that I would not even consider replacing the impeller--off to a shop to deal with that BS. I'm spoiled on my boat, but I've done it in as little as 20 minutes.

Someone had a repair kit that worked,,,,don't know if still around

Thanks all, I will be attacking this on wed.

All the posted info above is spot on. The more room the easier the job will be. I only have a few inches clearance between the front of engine and rear seat backrest. Having to access strictly from the side makes it tougher especially if you have the gen 3 cool fuel box. A few tips.....

You don't have to remove the serp belt. Zip tie it together or to a pulley once or twice before releasing tension. This makes it much easier reinstalling as you only have to guide it on seawater pulley and idler. Cut zip ties and done.

Backflush your raw water side of cooling system from heat exchanger back, oil and ps coolers. This ensures a clear path for water flow. If you remove your old impeller and it's chucked some vanes, it's essential to flush that rubber out.

When you get your seawater pump apart inspect the inner housing where impeller rides. If it's worn and you can catch your fingernail on anything it needs replaced. Mine was like this and I used an aftermarket Marine 496 rebuild kit for the stock housing. Hardin's stainless kit is the way to go if you have the $$.