496ho oil pressure dropped
 

Hi does anyone have any ideas why my 496 would suddenly drop its oil pressure after running at 50 mph.
Was running about 40psi few minutes previuosly then I just increased the speed a little from 40 to 50 ran a few mins then heard the lifters clattering. Looked at oil pressure (15 to 20 ish) as I backed throttle right off to idle pressure dropped to nothing. No alarms came on.
Got a tow back and had a brief look. Cranked engine on starter no loud knocks, then started at idle briefly, now with oil having cooled a little oil psi just below 20, top end clatter still there but less than when it first happened.
Oil levels all good and new oil.
Have recently had sump off to clean up and do some paint work due to extenal corrosion also replaced crank seals but not done anything that I'm aware of that could cause any internal probs with engine???

Any advice or ideas?

Thanks in advance
Simon

Did the water temp go up a lot? Lack of water flow would cause the oil temp to go up a lot, thinning the oil.

Oil pick up in the pan could have came loose or cracked when you had the pan off.

Thanks for responding guys all ideas appreciated.

Oil pickup intact
Water temp stayed at normal running temp.

Have progressed a little since posting. Pulled engine out and dropped off pan. Not torn down any further yet but have found metal debris in pan some of the larger bits are about 1/2 to 3/4" long very thin and hard silver metal. Not sure what a cam bearing would look like if it had spun and detroyed itself. Would like to try work out where this is from before diving in for the full strip down.

Sorry to hear it's not something simple. You'll have to check the rod and main bearings too.

Piston skirts? What ever it is doesnt sound like good news

What really seems awesome to me is that you actually caught it before it totally exploded.

I would not be so lucky..

And if it were mine with metal in the pan, there's no reason not to strip it now. You'd wanna make sure you got all of the meal out of everything. Just my 2 cents.

Best of luck!

Take it apart for sure

Started stripping out, found no. 5&6 big end bearing obliterated.
Scoring on all remaining ends and mains. Quite a lot of corrosion on all bearings in bottom end. Crankshaft quite grooved around 5&6.

Just about to start stripping out cam and top end.

Motor had loads of external corrosion low down and a waterline around it just above sump level. Spent loads of time a month or so ago doing a big clean up and respray. Wish I had looked a bit deeper now while sump was off.

Although I'm not really looking for a horse power up rate (don't have the budget for anything big) thinking of contacting Raylar to see it's worth doing anything crank and piston wise to strengthen the engine as I am looking at a new crank or crank repair at this stage as a minimum. Would be interested in anyone’s thoughts on this.

500 EFI and your done!!

496 mag ho running hot
 

I have a 2002 nordic rage 25 foot with a 496 mag ho and run it in the phoenix area lakes only fresh water.. water temp is fine at begining of the day but after running at higher rpms it seems to get hotter but not overheat and then when coming of plane to an idle it gets hotter and begans to overheat. but before it does i put it in nutreal and run it at 3000 rpms for a few seconds it cools back down to normal . any ideas of what it could be i just put in new sea pump and impeller. thanks

Impeller and the sea pump may have some grooves in it and need a rebuild kit.

Did it do this before the new seawater pump went on?
Could be sucking air if there was any bad connections in the plumbing before the S.W.pump. Make sure the winterisation system has no pressure in it. Check all the hoses (hoses may look ok on outside but can colapse inside), hose clips and fresh water flush if you have one. The heat exchanger could be partialy blocked easy to remove the ends and rod through the tubes. Also could be on fresh water side, check to make sure this is circulating properly. One easy check you could do is to put your had on all of the fresh water hoses and see if there are any cold areas in system. Further to this you could remove the thermostat and test it.
Hope this is some help.
Good luck. Be good to know how you get on, keep asking if you have no luck.
Si

525 and I would be weeeeeell done!! but it's the age old matter of available cash. Under the impression the 496 aint a bad lump if looked after...

That's very true but like everything else, there's been more than one that broke due to various reasons and suddenly they're junk.

Don't run it hot and keep good oil in it. I tore mine down after running the livin' crap out of it for lots of hours.

Wasn't anything wrong either. If you run anything at wot for extended periods you will break it. Just how it goes.

when i first got the boat in may in never did it . then after changing the impeller it would do it right away at first start up then would release the air valve and run it in nutreal at 3000 rpms and would cool off. so i had the sea pump replaced and now only does it at idle after running it for a while. thanks for the help man!

Can you fill in the actual temperatures that you are refering to ie "at the beginning of the day", "gets hotter but not overheat", "cools back down to normal" and "begins to overheat" after coming off plane to an idle?

start of day temp on the thermostate gage is 170-180 when driving over 4000 rpm it gets up to 185-190 and when slowing down to idle gets up to 200 something then alarms starts going off and then i put in nutreal before it oveheats because im afrair to see how far it will go like 240 and run it at 3000 rpms it cools back to 185-190. the actual water temp is low 80's and ambeante temp is high 90's

Little bit of advise don't push it into this situation (overheat alarm on) unless very briefly for diagnostic/testing. You are likely to be causing piston / cylinder damage. Certainly don't let it go up any further.

The 496 is a very stout engine indeed so when they break they cost dollars to repair and dont get your nickers in a knot.....there not junk.

Break the engine as this one is and cost out the repairs.

A grand for forged pistons because lets face it, there not and now is the time to do it. Price out the machining etc, gaskets and bearings...Head work??? the whole repair has to be done properly and not pieced together. If you are not able to do this yourself the money needs to be spent and that is not chump change.

Price out the parts from Merc and tally up the repair and you will see how quickly you can spend 7 to 10 grand on the rebuild (of course it all depends on what is hurt)

At the end of the day you have a rebuilt 496 engine...no arguments there......but If I was to do it again it would be a 500 efi hands down.
Pull the 496 in and put a 500 efi in its place.
B.S. on comparing the 2!!

And SD if you are refering to my comment I in no way said they are junk, read my post again!!

do u have any ideas of why it would be running hot after driving it hard. it doesn't do it after driving at cruising speed

I would suspect a scored impeller housing or a small blockage somewhere in the cooling system.

I read your post. Reading comprehension is not something I have much trouble with.

I was not talking about you and I don't believe I even mentioned your name.

My opinion is probably not that closely monitored around here anyway so no need to throw the defense at me.

I do have a habit of getting involved in 496 topics only because it's something that I've pretty well figured through a lot of time and money.

I honestly don't care if you like or hate them. I just didn't want the guy to feel like he owned a total pile cause it broke.

A 500 EFI isn't the best answer either if you live in salt 24/7.

There, there....:coolcowboy:

Who said they were junk all of a sudden????

You can bore it .010 over or .060 over and get Wiesco pistons from Summit or get a crank, pistons and conn rods from Raylar. $1400 plus machining for $200-400. Re-assemble and your done. Or add the Raylar heads and/or more. Since your engine is toast, it has no resale value. You can buy a 525 or 500 but you are out big cash. Rebuild the 496 with Raylar - he has a great forged package and you can be up and running with a lot more HP for under $10K or stock HP for $3000 (if you do the re-assemble)

I've done the math 100 times and I am 80% thru a 496 rebuild - If your engines are low hour you can sell them but for a high hour motor or one that is blown up, the rebuild is much cheaper

Keith you are right about the blown engine, it is only worth making it into a bar stool with no resale value.

The reason for the high temperatures is that the cooling system is compromised somewhere and can no longer handle the engine heat build up especially from hard running. Reduced flow of sea water or the engine coolant do to blockage or bad pump or sucking air or ....
Common cause of blockage in the sea water plumbing is do to rubber peices from a damaged pump impeller if that has ever happened to your engine. Check the coolant thermostat....coolant level. Check for pinched sea water intake hose at the drive or anywhere else. I am assuming that the engine coolant system is not choked with corrosion from worn out coolant. I have heard that the remote sea water dump drain valves and check valves can cause cooling problems as well. I think you get the picture.

Thanks for that, thats the sort of information I was hoping for.
I'm a marine engineer so it's gonna be a self build. Budget is tight but I wanna do this to last so its worth spending a little extra.
Are Raylar sometimes a little difficult to get hold of? I've sent a couple of messages but no responce.

Thanks again
Si

Best thing is to call Ray at the shop.
Curious to see where the forged rotating assembly comes in price wise.

Just spoke to Ray, great guy to talk to. After a bit of advice thinking of going ahead with some bits. After I save up a bit a money...

In answer to your curiousity Verbi Piston/rods/rings/pins kit $1426, Forged Crank $850, Full engine bearing kit $296

Will update when project underway cheers.

Thanks for the info Simon, go with the forged items.