Harper220

I have a 1999 Challenger SV-24 with a 496 Mag HO. I can't get the darn thing to circulate water correctly without revving it up and waiting way too long before it comes out my thru-hull exhaust. It ran fine last year (water circulated correctly anyway), until the starter failed late August. I had the starter replaced along with an oil change and winterize. Now I have my problem after it sat all winter. I took it back to the guy that winterized it and he had the boat for over two weeks with no luck. He stated that he replaced the impeller in the sea water pump and checked all the hoses. I finally picked up the boat and messed with it myself. I ended up pulling the transom inlet hose and jammed a garden hose into it a few feet till it stopped, blasted the hose wide open, started the boat and revved it to 2000 rpm and finally had the water circulating. I thought I was getting somewhere till I hooked it back up to normal and put the water muffs on the outdrive and nothing. What it boils down to is that I have to rev the hell out of the engine to get the water pump to finally pull like it should. I down loaded an exploded picture of the water circulation hoses and how they should be routed from mercruiserparts.com (BAM Marine) and I'm puzzled about the transom inlet hose being connected to the top fitting instead of the bottom one on the drain valve. It shows the opposite on the exploded picture from BAM, but tried to switch them and they are different size hoses and connections. What the heck is going on? Any suggestions or advice would be appreciated. Thanks

rv

I would suggest to start by checking for anything blocking the coolers or the heat exchanger. If that doesn't explain it then start by pulling hoses until you find a good flow of water. For example, pull the hoses to the exhaust, start engine and see if water flows good out the hose. Only run for a couple of seconds, you don't want exhaust riser to heat up and melt your 4" rubber hose. If no water or slow flow go 'down stream' to the next hose and check.

Rick

WesSmith

I believe there's been a couple of recall / service notices on the 496 related to the cooling system or something to do with the potential of water seeping into the bilge from a fitting. Ask your Mercruiser tech to look your serial number up and check.

Reckless32

Ensure the bolts on the impeller pump are tight and not sucking air. If you have both the upper and lower water pickups on your outdrive get in the habit of placing a strip of duct tape over the lower pickup when flushing. If you are in an area/beach, etc. where you may routinely suck up sand into the pump itself, there's a possibility the pump lining is scored and even with a new impeller, good suction won't be accomplished without high rpm's meaing the pump itself will need replaced. I bel;ieve that would be in the neighborhood of around $400....Do the simple stuff first. Replace the impeller again yourself. Put a little grease inside the pump so that when it initially primes, it won't heat up the impeller. Tape over lower pickup area. It will be slow to prime at first, but give it a couple shots of throttle and after it primes and puts out water, let it sit and run for a bit. Shut it down. Allow the drive to drain a bit as it does normally with tape off. Re-tape re-start. If no water again. Replace pump housing.....

Kentz

I had the same problems with my HO's. I have lower and upper water holes. Even with lower holes taped over, I could not get water for 2-3 minutes at idle. Needless to say, I fried the impellers. Since my boat was new, my tech got me new pump assemblies and guess what?, he tried it on the hose and after 1 minute saw nothing and shut it down. Backed it down the ramp and all was fine. It left him scratching his head. Some guys say you need 15-2000 rpm, not in my driveway

I'm probably being over -conservative, but I will not start these engines out of the water! My guess is that the heat exchangers add a lot more back presure than a conventional wet block. Still, you may have a totally different problem.

BillR

I too have same problem. I just run the motors up to 1500 rpm after oil pres builds. Once that is done it works fine.

I found this issue last winter when I tried to fire up motors after winter. I just started motors and they got hot. Had merc tech come down, and the first he did was rev motors. Worked fine.

bikinilover

I have the same problem with mine on the hose, put it in the lake and it is fine.

Harper220

I "have" put the boat in the lake and it takes forever to get the water to start circulating and sometimes not at all. It simply shouldn't take that long. Also, you shouldn't have to rev the motor just to get it to work properly. It worked fine last year. The part about the picture I found at BAM Marine is incorrect. The seawater inlet hose connects to the top fitting of the air actuator on through to the sea pump then back to the bottom of the air actuator then it y's off to the starboard exhaust manifold and on to the other side of the motor. There has to be some sort of restriction somewhere or the sea pump impeller is shot again. Does anybody know if the main water circ. pump would have anything to do with the prob? Good God, I would like to go boating this weekend!!! Thanks for all the replies. I'm gonna dig into the sea pump and check out the impeller.

BillR

I think you'll find the impeller to be fine. What you may see is grooves in the pump housing SOMWHERE. If so, new pump time and you will have found your problem.

Let us know your findings.

AZDominator

I've never had a problem circulating water through my HO's. Try cycling your pressurized flushing system a few times to make sure the valve is functioning properly. You did say after it was winterized so this is the only related system that was messed with.