496 Temporary Overheat?
 

Hey guys...new to this boat and the 496. This was my first time out with this Ultra and it had been sitting about a week and a half since it was in the water last. When I launched it, I had to idle in neutral in the marina for a few minutes while I waited to pick up my buddy. About 5 min into idleing, a overheat alarm went off. Gauge only showed about 150 but still alarming. I lifted the hatch and felt the manifold and about melted my hand off. Turned motor off for a minute then started it back up. Alarm was still going off but gauge still only showed 150-160. I idled in to pick up my friend and spun around to idle out of the marina.....alarm still going off. After about 1 minute of idling in gear and then getting onto plane, the alarm shut off.

so obviously, when sitting still, the motor wasn't pulling in enough water to keep cool. so my question is, is that "normal" for that to happen the first time back in the water since all the water was drained out OR do I have some sort of pump/impeller issue? The dealership told me they put a brand new pump and impeller in it right before I took it home.

thanks guys.

haw many hours on engine?? hate to tell you this but the 496 engine seapumps are known to go bad andare expensive to fix..i recomend getting the hardin or cp performance one this way is wont go bad so fast..the after market is a better design and cheaper then the 600+ dollars that merc wants for their junk..http://www.cpperformance.com/p-15774...d-502-mag.aspx

Since you mentioned the impeller was replaced I would lean toward what could be wrong due to that. Either they really didn't change the impeller and should have or they did and used the air system to drain the water out and didn't release the air from the system afterward. Just a thought. Was there extra water in the bilge? Or like FIXX said, pump itself a common problem.

motor has 125 hrs on it. it got a new seawater pump along with the impellar when I bought it (at least that's what they told me). no extra water in the bilge either.

if that is the case then replace the water pressure sensor,,those are common problems as to they plug up with chit and wont register at low water psi..when the water temp gets to 190~220* then start to worrie..

thanks man i'll check it out. where is that sensor on the motor?

How old is the motor? Has the antifreeze been replaced? The AF should be bright pink/peach. If it is grey/metallic it's old and needs replaced. It silts up and and does not flow as well. It's only good for 6-7 seasons max.

Also, do you have a fresh water flush connection on the boat? Make sure the cap is closed AIR-TIGHT if you do.
Sometimes, those systems have spring loaded check ball systems that can get gummed up with sand, weeds, and debris from the water; which also cause overheats.
You could have an obstruction that is not allowing enough flow at low speeds, but adequate at higher speeds.

If you do not have a water pressure gauge, it's advisable to have one. If you want to see an overheat via alarm or gauge, it's too late and your impeller has started moving through the cooling system. A water pressure gauge will tell you if you have picked up a bag or something on the drive and restricted waterflow immediately.

I've also posted many times before, that you really owe it to yourself to buy a www.rinda.com scanner for that motor. It will save you hours upon hours of troubleshooting time. It's the best $500 I've ever spent on any boat.

Coolant looks brand new. no obstructions in any of the water pickups either. Im going to back the boat in the water in the am and let it idle on the trailer to see if it happens again.

Im not sure about the freshwater flush cconnection...is that supposed to be on the drive?

Im either missing the sarcasm here or you didn't read the part where i said it got a new pump and impeller???

Fresh water flush connection would be a garden hose connector somewhere in the engine compartment or perhaps on the transom. Some manufacturers install them, and some do not. Do you have a sea strainer? (small little coffee can looking thing in the bottom of the boat with a clear window and a basket inside to strain out seaweed and debris before it goes in the engine)

Maybe the water pump hoses were reversed upon reinstallation, during the impeller change. Check that and the impeller-they frag very quickly without water. Was the transom bellows and hose serviced? Its easy to twist the water inlet hose and restrict flow.

It's going back to the dealership this morning.

I'm hoping there's no internal damage to the motor....

http://m.youtube.com/watch?v=uLX6kvWKNJc

stock 496 have 160 thermostat so they they run about 180-190 and if they over heat computer shuts it down I say you will be fine ,open the right side of the heat exchanger and see if its has any blockage . I do not think its a cooling issues .check your iac motor. please let us know what you find

be very careful, in my opinion 496 is a grenade, turn the key=pulling the pin..see to many fail with low hours for B/S reasons...working on one now volvo POS 30 hours, internal fuel filter clogged(have to replace fuel pump..big $$$$ and now killed a piston...volvo no help even with 30 hours....

so I picked the boat up from the stealership today. apparently it needed a new sea water pump after all. i KNOW they told me that they were putting in a new one before I took delivery but today they told me that they said they only replaced the impeller. If I hadn't thought I got a new one to begin with, that would have been my first thought but it is what it is. Thanks for the suggestions guys.