Why, why, why 496 HO overheating?
 

I've got a big investment in a 28 Daytona with 496 HO's. It's a 2001 and had 10 hours on it when purchased. I had both sea pump impellers replaced at start of season and one engine keeps running near 180 deg. when boating on the Missouri river, but runs fine at lake of the ozarks. The engine goes into guardian mode and loses power at the 180 deg point. Is this really that hot on this engine? Are these sea pumps really that unreliable? What else might be the problem? When I look at the through hull exhaust, there's plenty of water circulating, just as much as the other one. I'm getting very frustrated that I spent !@#$% on a boat and I have to worry about overheating.

Any ideas or input would be appreciated. Could it be something else?

Re: Why, why, why 496 HO overheating?
 

So you are seeing a engine temp difference between the two bodies of water? On both motors?

Re: Why, why, why 496 HO overheating?
 

How were the impellers you pulled out? If one was missing parts they could be clogging somewhere in the system. Try backflushing.

Re: Why, why, why 496 HO overheating?
 

Caincando1- I have analog gauges, so as far as I can tell the engine that's fine runs about the same at lake or river.

obnoxus- The engine that overheats had the impeller that had all the veins missing, but the guy that replaced it said he backflushed everything out. You know how that goes though.. What's the easiest most effective way to back flush to get the crap out if something were still in there? Where would be the most likely place that something might be stuck? I need to get this prob fixed.

Re: Why, why, why 496 HO overheating?
 

Theres your problem, backflush and I bet your fine. Start pulling hoses and flushing water through them. Its a pain in the ass.

Re: Why, why, why 496 HO overheating?
 

Harper, I am in St. Charles whats the guys name that did the work. I have a 496HO I just got installed and no problems so far. If you need someone else to look at it PM me I got a guy that is really good with that engine.


Rich

Re: Why, why, why 496 HO overheating?
 

The way I did it was to pull the hoses and flush them then pull the thermastat and flushed from the bottom drain plugs on the block, made fittings to connect to my garden hose, got nothing at first so I connected a air hose with 100 psi to the bottom drain plugs and shot that for 30 sec. then did the water again and the pieces started flowing out.

Re: Why, why, why 496 HO overheating?
 

i pitchure PIECES somwhere too,my .02

Re: Why, why, why 496 HO overheating?
 

Ok, here is what happened to my 496 ho today. The port motor kept going into gardian mode and alarms ringing, all gauges were ok. This would keep happening intermitently. I used the scan tool and found that port motor, port exhaust manifold ran at 106 degrees, starboard ex man. port motor 205 dg., hooked it up to the starboard motor and both manifold ran 105 and 106....... all manifolds felt same to the touch..... I took both temp senders out of starboard manifolds of both motors and switched them and problem moved over to starboard motor.....the sender looks to be the problem, will change it tomorrow and will post the results. only 30 hrs on motors.....

Re: Why, why, why 496 HO overheating?
 

Rich- A guy that works for Boat Docs at LOTO changed them. He seemed to know what he was doing, but then we're all human. I keep the boat where I live in SW Iowa near Omaha, so you're a little ways away. I wish there was somebody decent to look at it around here. I won't deal with the Eliminator dealer just 15 miles away. Don't even ask..

Backflushing sounds like a good place to start and by the sounds of it Tricky is on to something. I actually talked to a few others and the senders were brought up as a possible problem.

Are the senders capable of sending a false temp reading to the ecm and triggering a false alarm? I guess it makes sense..

Thanks guys

Re: Why, why, why 496 HO overheating?
 

Seems to me if the motor is going in to guardian mode it should set some kind of alarm condition that could be checked later with a scan tool. I know nothing of Mercs program so I am probably assuming something I shoud not. I like computer controls but I really hate programmer's that do not include any trouble shooting or service provisions in there programs.

Good luck and I know on 502mag oil coolers are most likely spot to be plugged with trash from impellers. Shell and tube cooler and sometimes you have to remove the cooler and run a rod through tubes to get them all cleaned out.

Re: Why, why, why 496 HO overheating?
 

Just another thing to peak at, take a look at the hose feeding the pump, and make sure it is not kinked anywhere, and that the clamps are tight on the back of the pump.
We had a bad hose feeding the water pump, kinked at the transom, and loaded with crystallization that reduced the inside diameter of the hose down to about 1/4 ". Motor would run fine under 3200 rpm , but as soon as you went above that the temperature would climb.
Good luck and post what you find.
Brian

Re: Why, why, why 496 HO overheating?
 

Harper,
Something you may try, facing the front of the engine the lower hose, on the right hand side of the heat exchanger ( about 1- 1.5" diameter) can be removed, then remove the 2 blue drain plugs from the sea water pump. Hook up a water hose to the hose you have removed and back flush the engine. This is a quick, and easy way to flush any blockage from the oil coolers. Especially if you have twins, and access is difficult. I found a common fitting at the hardware store, that would allow me to clamp to this hose and get good pressure back through the system. The amount of debris that came out was alarming. You are definitely having a water flow problem if the exhaust is getting this hot, on the one side.

The back flushing may resolve this, but if this does not work, do not rule out, your pump housing may be worn out. As I said in an earlier post, I had to replace both of mine after 60 hours. The brass housings will erode in time in a river environment, and new impellers will not help, if they are worn out.

One other possibility, the 496's had an issue with the fittings on the lower side of the exhaust manifolds corroding and breaking. A recall was issued to replace these a couple years ago, to replace the original brass fittings, with aluminum ones. Even if this is not your problem, I would make sure this has been changed, before it is a problem.

Good luck, let us know what you find.

Re: Why, why, why 496 HO overheating?
 

Ok. here is the result. I changed the manifold temp sender and poof the problem is gone. The part has been superceeded three times already by merc.....I wonder why? Harper to answer ?, Yes it did log a manifold over heat in the comp... So basically the motor was running perfect and the bad sender caused it to go into gaurdian mode and all the bells and whistles to go off.......

Re: Why, why, why 496 HO overheating?
 

That's why I asked the other day if everyone is happy with Smartcraft. I have a few friends who have the same thing happening. Alarms and whistles and no fire to put out. It's called ruining your boating day.

Re: Why, why, why 496 HO overheating?
 

I think they over did it with the sensors......There is something to be said for simplicity. I did learn how to use the merc scan tool though......

Re: Why, why, why 496 HO overheating?
 

I ran the boat Saturday and had my scan tool hooked up and the port exhaust was heating up to about 212 deg. and that's where the guardian mode kicks in. I know it's not a bad sensor since the riser was extremely hot to the touch compared to the others. Also when I look at the through hull exhaust the port is steaming and the others are not, so it's definitely getting hot. I pulled the boat into a marina and let engine cool then pulled the hoses that go into the bottom of the manifold and the big one on the heat exchanger and blew through it. then I started the motor to see if I had pressure and it seemed to have plenty. Hooked everything back up ran the boat 25 miles at 3600-3800 rmp and even into the 4000 range and temp never got over 175. Stopped at a bar on the river for a while then when heading back down river the dam thing was right back to heating up again 190's. The starboard manifold runs around high 160's to low 170's.

There has to be something restricting water flow to the port side. I will back flush the system like Island Hopper explained. I hope this fixes the problem. If the other manifold is staying cool then I can't imagine the sea pump is bad, thank God.

Any other advice would be appreciated from anyone following this thread.

Thanks

Re: Why, why, why 496 HO overheating?
 

What solved yor problem?