NEED HELP with a 7.4L

[Chad33]

I have a 1997 SeaRay 240 overnighter with the 7.4L mercruiser. Im pretty new to boating so any help would be appreciated. Today I was out on the river cruising at about3000rpm when my tach suddenly went haywire and dove to 6000rpm without the motor ever increasing. And then suddenly, the motor began to bog down. I quickly scanned the gauges and saw that the temp was at 200F when the hottest it has ever got was 170F. So I shut her down and let her sit for 20-25 minutes. when I went to start it back up. Nothing happned. it was like the motor seized and the starter couldn't overcome it. Also I noticed a leak coming from somewhere in the engine compartment. it was definitely the fresh water, I just couldn't tell where it was from. So when I got home this afternoon, I hooked up the hose and tried to start her again. this time she cranked. After a few tries I was able to get it started but only for a few seconds before she died. I was able to hear what sounded like air escaping from the rear left cylinder head. So my thoughts are that I blew a head gasket at the very least. And there was no sign of any water in the oil when I checked it. Do any of you have any thoughts as to what my problem is, and what caused it?

 

[Chad33]

Also, a few days ago, When I started the motor. I noticed a gurgling sound from somewhere in the engine compartment. After I revved it up, the sound went away. Could this be the water pump or a busted hose?

 

[Air O'Nautical]

Sorry,

Way too many variables to guess...

I'd start by pulling the plugs, see what they look like. A trained eye can get a good idea about an engine's health by "reading" the plugs.
(I don't have a trained eye but, the Internet is a great learning tool, if your like me).
A compression test is easy with the correct tool and will expose the health of the motor but, may not pinpoint the problem. It will make the decision if you need to pull the heads off.

Lets back up and look for simple things.....
Is the ingnition cap on tight? There are 2 hold down screws on the sides..
Is the distrubitor tight? Try to twist it...there's a single hold down bolt into the intake manifold.....if its loose the timing is all wrong.
Is it getting clean fuel under enough pressure? Filter? Fuel pump? Fuel in the tank?

Man, I'm all over the place .....guessing. Like I said lots of variables.

Start digging in and let us know what you find.

Best,

 

[src]

I know that you said you didn't see water in the oil, but you could have a leak in the manifold(s). If so, you can hydro-lock the engine, which is highly destructive. Don't test it by running it any more until you eliminate the possibility.

 

[JimG]

I agree with src... possible hydro-lock. Remove all of the spark plugs and crank the engine over several times... see if any water comes out of any cylinders.

 

[Saverio]

plus 1
how old are your riser?

 

[Air O'Nautical]

Yes, check the manifolds, elbows and risers (spacer between the manifold and elbow) if you have them.
If your leaking water into a cylinder that spark plug should seem very clean from being steam cleaned.

Happy hunting,

 

[Nehalennia]

Sounds like hydrolock to me too.

 

[Saverio]

can you disconnect the water line coming from the outdrive and let the motor run without water for a min or two and see how it acts. if all seems ok you have an issue wih rises manofolds

 

[Nehalennia]

can you disconnect the water line coming from the outdrive and let the motor run without water for a min or two and see how it acts. if all seems ok you have an issue wih rises manofolds

.....and sacrifice the impeller? This is a bad idea and advice. It's time to pull the plugs as suggested, turn it over to see if water comes out, then inspect the manifolds for leaks. It really sounds like the manifolds and risers are leaking.

 

[scoflaw]

Hydro lock wouldn't account for his overheat or leak in ER. Pinpoint these noises your hearing.

 

[Nehalennia]

Hydro lock wouldn't account for his overheat or leak in ER. Pinpoint these noises your hearing.

Well the manifolds could be clogged, which will overheat and from that expansion, give way and then leak including inside and out of the engine.

 

[scoflaw]

Manifolds aren't going to clog suddenly like OP describes the event happening

 

[src]

Manifolds aren't going to clog suddenly like OP describes the event happening

But at this point, any advice that includes running the engine as a diagnostic is bad advice. Eliminate the disastrous options before chasing the little stuff.

 

[scoflaw]

He hears air escaping, he may be correct with a blown head gasket. How bout he pulls all the plugs spins it up and does a compression check?

 

[Chad33]

Alright guys, sorry for the delay. I was able to find the problem. Turns out, the Sea water pump bearings went to crap. So I was extremely lucky that merc set up both the fuel and water pump to run off this. Saved my motor. I was able to rebuild it and get her going today with new parts and impeller kit. However, after first starting her back up, the new impeller did not push any water and brought me back up to hi-temp. I shut her down and began forcing water through the lower unit. My problem was now the impeller again. So I took her all apart again to find the both the impeller and housing needing replaced. Am I missing something on this?

 

[Air O'Nautical]

Are you a Bravo II or III drive with the raw water pump on the motor?
(that would be the same as mine, even though I'm an inboard)
If so ensure the hoses are on correctly...mine has the raw inlet on top of the pump shown in the pic below..
The bottom hose off the pump is the outlet to the cooling system.

 

[Chad33]

So I was out playing with it this morning. This is what I can further tell you. I was not able to get water to flow from the outdrive up through the inlet hose. But when I reversed this, water poured out of the outdrive. I wasjust about ready to throw $600 dollars at purchasing an all new sea water pump assembly. But, since Im not even getting water to the pump itself. Where should I start?

 

[scoflaw]

Possible air leak in the water intake line from drive? Some pumps don't do well in the driveway on muffs. Take it to the ramp.

 

[Chad33]

I originally replaced the impeller and then took it out on the river for what I thought would be a day of boating. But before I could get far enough away from the dock, she over heated. Got it home, checked the impeller and she was toast. Bought a new kit and was checking the water flow, and there is nothing coming up to the pump. And she ran just fine off the garden hose until yesterday. So I am totoally lost now.