Did I blow the Powerhead? Heard an Alarm

[tomfsu]

Just purchased a 16' flats boat with a 02 Merc 125hp. I had an marine mechanic inspect it, all cylinders were at 120. I got it out on the water (after buying it) and it was a disaster from the start. Turns out the gas gauge was shot, ran out of gas...and drifted into weeds in the process. I had a friend bring fuel and I tried my best to keep the prop out of the weeds.

I started her up and was cruising for about 10 minutes, all the while the rpms kept bouncing around and I couldn't get it steady and it was running about 1/2 the speed of normal, I looked back and it was pissing water the whole time. Then an alarm went off, it was a constant alarm not a beeping one. Within 10 seconds I had the boat powered down. I looked at the prop and I had some weeds tangled on the left side of the water intake (not sure if this is correct term). After about 5-10 minutes the alarm stopped.

I had to get towed back to the shore. My mechanic tells me that the Third cylinder is now only reading 85 and that I will need a new powerhead! Is it possible that I did all of this in such a short time with a few weeds? Please tell me I bought a motor that was on it's last leg and that I didn't kill it that easy. This would be like driving my SUV over a curb and totaling it!

 

[CharlieB]

Re: Did I blow the Powerhead? Heard an Alarm

Marine engines operate at FULL LOAD.

Alarms mean one thing, TURN OFF THE MOTOR IMMEDIATELY.

Turning down the power isn't enough. Continued operation of the motor can, and often will, do damage.

Do you need a NEW powerhead, I doubt it, replace the one piston, re-ring the rest while you have it apart, next time an alarm goes off, shut it off until you find out what's going wrong.

 

[j_martin]

Re: Did I blow the Powerhead? Heard an Alarm

These large outboards burn a lot of fuel, generating a lot of heat. If they aren't running just right, they can do major harm to themselves in short order.

I think you had several things against you. One is that the cooling was partially blocked off. I've had that happen on a v6, alarm went off, stopped cleared the debris, and no harm done. It was only a single fault. (overheat)

You said it was acting up. It's unclear, but I think you are trying to tell us the motor was gaining and losing rpm's, and maybe not responding as expected to throttle. You might have had a fuel problem with the one cylinder. If it was running lean, it could burn a piston. Cooling malfunction would make it worse.

If you have the power head worked on or replaced, be sure to look at the fuel system with a jaundiced eye before you put it back into service.

hope it helps
John

 

[tomfsu]

Re: Did I blow the Powerhead? Heard an Alarm

Thank you both for the insight. To clarify, I did turn the engine off within 10 seconds of the alarm. The mechanic advised that I shouldn't just fix the bad cylinder, instead I should replace them all. Is that accurate? I was quoted around $2,000.

 

[j_martin]

Re: Did I blow the Powerhead? Heard an Alarm

There are many racing engines in service, working way harder than yours ever would, with 1 or 2 oversized pistons in em.

On an outboard you replace what's worn. If the other cylinders and pistons are in good shape, don't replace them. If the rings show any wear, replace them. Renew the bad hole (which may be just an acid wash) and replace that piston.

In short, a good mechanic won't even give you an estimate until he tears it down and looks at the pieces. He could give you a range, which typically would be quite wide.

The big thing is don't just renew the power head and try to run it. Find out why it burned down one hole first.

hope it helps
John

 

[tomfsu]

Re: Did I blow the Powerhead? Heard an Alarm

John, I have a few questions:

1) Very rough estimate - How many hours of labor for a mechanic to tear it down and look at the pieces to provide an estimate? Is this an extensive process?

2) Very rough estimate - If the hole was renewed, one piston replaced and rings replaced....roughly how much would that cost?

Thanks,

Tom

 

[j_martin]

Re: Did I blow the Powerhead? Heard an Alarm

I don't know how much time it would take. A fresh water motor usually comes down pretty quick. You can spend a lot of time on the fasteners if it's been anywhere near salt.

seems costs go by coupla hundreds. coupla hundred for a piston, coupla hundred for a sleeve, a rod, etc. That's why a good mechanic can save you many hundreds by not replacing parts that don't need replacing.

Maybe a real pro can chime in with some costing help.

John

 

[tomfsu]

Re: Did I blow the Powerhead? Heard an Alarm

Thanks John

Any insight on repair estimates from someone experienced with this problem would be helpful.