I have a Velocity 260 (boat isn't really relivant) with a 496 Mag w/Bravo 1 Drive.

Everytime I try and run it off a hose it fails to cool the exhaust, basically no water flow. So I took it to the ramp and dropped it in the water, started it up and agin no water!. The impeller housing remains cool to the touch. So I pulled the petcock on the Impeller and water comes out. I replaced the petcock, started the boat again, and again still no flow of water..... So I pulled the petcock once again and this time started the motor with the petcock out. As expected water began to really pump out of the housing. So I shut the motor off and replaced the petcock. Started the boat again and within about 30 seconds, I now have full water flow through the exhaust......

This is the first time I have started the boat this season. It did the same thing last season (at begining). Also at one point last year I flushed the raw water cooling, and then tried to run the boat on the hose, and again same situation...

It is acting like it is getting some sort of Air Lock and it needs to be burped.....

Is this normal behavior for this motor? If not any ideas on what can be causing this??

Also, completly unrelated. My Drive Trim seems to be acting really slow. It takes almost 1 minute for Drive up to drive completly down... I cycled it a few times and it seems to be faster, but still not right... Does it sound like it needs to be blead? Or does this sound like pump motor?

Add to it looks like my alternator took a crap as well. Way to start of the spring. I am already close to 4k in interior work.... It is going to be damn pretty sitting on the trailer!

At least alternators are cheap and easy to replace. I suspect that the slow trim might be due to low voltage, but it could also be due to the weight of the fluid in the trim pump. If I recall correctly, the normal fluid would be 10w30 motor oil for the trim pump. If you used something heavier perhaps that is the cause- use a pump or a turkey baster to suck out the oil fluid, then refill with the correct fluid (double check what the correct fluid is for your pump).

While seeing as I mentioned the Alternator was done, low voltage would normally be a very good suggestion. However, becasue of the amount of stereo equipment in my boat, voltage isn't an issue as I have plenty of battery (1 group 27 and 2 group 31). As a matter of fact, for all I know the alternator could have crapped anytime last season. I charge my batties every time we go out so who knows when the alternator went. With that being said, I opened up the resivor for the pump and the fluid did seem a bit thick, how or why I have no idea..... So I will start there, remove the fluid and replace.

And yes alternators are cheap. ANy suggestions on where to order upgraded (more amperage) alternators for the 496??

I have both group 31 batteries wired in parallel on the #2 position on my battery switch. Occasionally I forget to swith to Battery #1 (running battery). So I am guessing the strain of trying to charge 2 group 31 batteries was the casue of my failed alternator... While an isolator would help the situation, I only use #2 when jamming the stereo and charge these batteries with my on board 30amp charger..

As far as your cooling problem, would a scored housing or a worn out impeller that's still intact and not brital cause this?

I had this problem last year and my housing was scored a new impeller will not be a good fix.I bought new pump and had old one redone for a back up.

Would suck to get on the lake and have it crap out when you get to other end. Mine would not move enough water to cool any over idle.

ck the impellor, also may have peices from a old failed one clogging the oil or p/s cooler restricying water flow

I dont know how much credit to give it since I have never heard it anywere else, but the service manager at the local marina told me that if you run a large bank of deep cycle batteries in a boat you will burn out alternators really fast. Said it is because they never fully charge, are always drawing a load from the alterator, cycling it more often, and more batteries makes it worse. Recommended only using starting batteries, said they have had this happen a lot.

If fins off impeller is missing wouldn't hurt to back flush hoses with garden hose. clear lines from any blockage "material'.