overheating question??

[Dilligaf]

went out today with no problems. when i got home went to flush engine with earmuffs and it overheated.. well got close.... thought maybe i had a bad connection so tried it again about 5 min later and did it again... any opinions?? oh yeah 2006 5.7l mercruiser mpi...thanks

[McGillicuddy]

Nice big bass drum, Dilligaf. Is your engine fresh water cooled? You've probably already covered these thoughts but here's what comes to mind first. You can hope it's the thermostat, more often than not changing that is wasted cash, but at least its cheap. If its a freshwater cooled system, make sure the radiator cap is not leaking. if air gets in the system engine will quickly boil over. Check relevant fuses (temp gauge) Check your belts -- is the the serpentine belt driving the water pump look worn? shredded, torn? - it could be slipping. Fire it up and watch it. Could be the impeller is shot -- is the pee hole pumping water? Test the water pump -- push and pull on it, if there is any fore and aft play the waterpump is shot. Could also have picked something up & its impeding your water circulation, baggie, weeds,whatever. Exhaust risers water jackets could be clogged but unlikely on something so new. Good luck.

[gofastsandman]

Nice fish Dilligaf! Are you on a well? Sometimes they wont put out enough pressure. I`m always careful when I flush my rude as the muffs tend to slide away from the pickup. I saw 180 on the gauge once and it woke me right up.
gfs

[oldfielder]

Are you supplying water through the outdrive or a dedicated thru-hull for cooling this boat?
If it hasn't overheated fully, that's a good thing.
If the boat ran fine at the water but not the driveway, the first thing I would be checking for is restrictions in your water flow. There are many places this could be happening, but one of the easiest ways to check initially is to see if you have good, steady water coming from the exhaust ports on your transom assembly.
I know this sounds ridiculous, but definitely check if your hose in the driveway is compressing anywhere from the suction created by that seawater pump-once it gets going if pulls pretty hard to cool a big motor like that.
It seems strange that you would get home and have this happen after running the boat fine.
If it is fwc, one of the easiest ways to check if you fried the impeller on the seawater pump is to pull the end cap off of intake side of the heat exchanger and see if there is any crap in there-bits of rubber in this case-if there is any, then you will know immediately where your problem is.
As previously suggested, it could be your thermostat, but is seems strange that it would go bad between the ramp and your house, although most stuff that happens on boats happens at the stangest times.
Feel free to pm me if you have any questions-I have the same engine block and may be able to help with further diagnosis.

[1bayouboy]

What RPM do you run to flush it...???
I have to run 1200-1500 to get enough cooling water flow from the hose to cool the FWC engine through the heat exchanger.

[1bayouboy]

Get a Smartcraft Monitor and you can see the raw water side pressure......on the hose with a new impeller mine is around
2psi. I haven't tested it in the water yet with the new impeller but should be 10 PSI or better.

[Dilligaf]

its raw water cooled and i just let it idle when flushing.. do i need to run higher rmps when flushing. heard it might be my impellar since when running on water was fine and at idle flushing heated up

[1bayouboy]

I'm not sure about the RWC engines....mine is FWC and it definitely will overheat at idle on the hose.....but it'll run all day at 1200rpms and stay on 160 degrees.

[Dilligaf]

thats hopefully it. the hose is kinda small diameter and looked like a lot of water comeing from the muffs leaking. it only got to 3/4 temp when the alarm went off engine should be ok turned it off right away