Crap! Overheated and big trouble!

[fredcrn]

OMC 5.7L GM inboard with 260 hp outdrive. Engine overheated last time out. Took it home and checked water pump belt. Was loose, so replaced it. Ran engine with water to outdrive muffs and had water flow from intake hose. Thought maybe I had it fixed. Took it out on the water and was throttling up when the temp guage suddenly jumped into the red. I shut it down quickly and paddled it back to the launch ramp (no easy feat) thinking I'd start it up to pull into the dock. When I tried to start the engine it wouldn't turn over. Took it home and pulled the plugs and water poured out of the cylinders. Cranked it over a bunch and eventually could get it to turn over with the plugs in. Guessing I'm grasping at straws here, but I've read that shutting down rapidly can cause a dieseling effect. If the outdrive pump is not functioning, could this still happen? I'm thinking the outdrive pick-up pump is pooched and the only reason I was getting water flow thru the intake hose was because the garden hose was forcing water into the system. Of course I'm concerned I've cracked a head or exhaust manifold. If I hook up the water muffs and crank the engine with the plugs out, if there is a leak into the engine, I assume I could see water spurting from the plug holes? Sorry for the long post. All responses appreciated.
Thanks
Fred

 

[a70eliminator]

Re: Crap! Overheated and big trouble!

Compression check for a blown head gasket, water in all cylinders is more than likely a bad exhaust manifold, a cracked block will quickly fill your oil pan with water too. Just from what I've read though I have no first hand exp.

 

[Don S]

Re: Crap! Overheated and big trouble!

Got a year for this OMC 5.7?
When it got hot and you shut it down, My guess is it dieseled and sucked water back into the engine.
If that is the case, clear the water and start it up ASAP, so you don't end up with rust in the cylinders.
As far as the overheat goes, when was the last time the raw water pump impeller was replaced? An old or faulty impeller is the most common cause of boat engine overheats.

 

[salty87]

Re: Crap! Overheated and big trouble!

how hot did it get?

got rubber exhaust hoses on that puppy? check em for soft spots if so.

 

[fredcrn]

Re: Crap! Overheated and big trouble!

Thanks for the replies guys. Here's an update. After reading some posts here, I thought I might be fortunate enough to have only experienced a dieseling effect. The more I thought about it, the more it seemed possible. I went from almost full throttle to stop in a hurry and am sure I remember the engine making a small chug sound as it shut down. Ok, so today I removed the spark plugs and cranked her over real good. Replaced the plugs with new ones and got her running. The engine is presently running as smooth as ever. I agree that the pick up pump in the outdrive is most likely the culprit. I have the repair kit and hope to have this repaired in the next week or so. Here's my question now...I know that even with the outdrive pick-up pump malfunctioning, I still get a slow flow of water from my muff setup. If I did have a cracked head or exhaust, would this slow flow be enough to cause the engine to hydralock? I ran it a bit above idle in the driveway for long enough that the temp guage was just approaching the green and it was running as smooth as ever. Did I get lucky? BTW...I don't have a pressure test setup at this time, but think I'd better pick one up. Also, there is no indication of any water in the oil pan.
Thanks
Fred

 

[fredcrn]

Re: Crap! Overheated and big trouble!

Got a year for this OMC 5.7?
When it got hot and you shut it down, My guess is it dieseled and sucked water back into the engine.
If that is the case, clear the water and start it up ASAP, so you don't end up with rust in the cylinders.
As far as the overheat goes, when was the last time the raw water pump impeller was replaced? An old or faulty impeller is the most common cause of boat engine overheats.

Hey Don,
Thanks for the response. I do think that the impeller is most likely the problem. Have the kit, now just need to find the time to install it. Means pulling the lower off the boat. Major pita, but do-able. I'm hoping you're right about dieseling. Have run it and all seems well so far.
BTW...boat's an '83 OMC outdrive with a GM 5.7L inboard.
Thanks
Fred

 

[fredcrn]

Re: Crap! Overheated and big trouble!

how hot did it get?

got rubber exhaust hoses on that puppy? check em for soft spots if so.

Thanks for the response Salty. Hoses all seem good. I'm kinda leaning toward Don's suggestion that I dieseled her.
Thanks
Fred

 

[fredcrn]

Re: Crap! Overheated and big trouble!

Compression check for a blown head gasket, water in all cylinders is more than likely a bad exhaust manifold, a cracked block will quickly fill your oil pan with water too. Just from what I've read though I have no first hand exp.

No water in the oil pan...thank god! Need to pick up a compression tester this weekend, but I think I might have gotten lucky and just dieseled her, as Don has suggested. Thanks for the response.
Fred

 

[getinmerry]

Re: Crap! Overheated and big trouble!

Replaced the plugs with new ones and got her running. The engine is presently running as smooth as ever.

A sure sign the motor is about to blow up

 

[THE BEEF]

Re: Crap! Overheated and big trouble!

If its a stringer the swivel bearing seals could be worn and sucking exhaust gases in the cooling water.This will make it overheat suddenly. It happen to me.
A OMC mechanic told me to pump about 9 shots of triple guard grease in the bearing. It sealed them right up and no overheating after that. Yes I did change the impeller first and the water pump. No help.
Beef

 

[fredcrn]

Re: Crap! Overheated and big trouble!

Thanks for that input Beef. I have the outdrive off and apart. Replaced the water pump assembly, the impeller was separated from the shaft. The swivel bearing retainer is probably the culprit here. Ordered a new one today. Probably could have just greased the heck out of the old one, but since I'm this far into it, I figured what the heck. Good news is, the shifter cable was a fairly recent install, so no problem with getting it out. Hope to be up and running again by the first of next week. Finding lots of interesting stuff, like missing bolts and stuff not greased properly. Local marine guy did the most recent work on it...that was when the shift cable had to be replaced. They apparently broke it. After seeing the way they did this job, I'm thinking they probably cut it to get it off, rather than fight with it. I think the 'new guy' worked on my boat and I can assure you of this, my boat is never going back there! I'm betting he never greased the swivel bearing when he put the lower back together. Jerk!
Sorry for the rant. LOL
Thanks to all for their input.
Fred