PLEASE HELP> First Boat - First setback

[Knot Waiting]

1989 Celebrity 23' Cuddy. 5.7L Mercruiser Alpha 1

Went out today and noticed that RPM's were running at 4000 instead of the normal 2ish. Then the engine temp warnig light came on. Vented the engine room and temp returned to normal but boat had a tendency to porpoise at speed. Any insight? I would like to know what Im getting into. Thank You - Logan

 

[Don S]

Re: PLEASE HELP> First Boat - First setback

If it's porposing, trim the drive down a little. The problem with that is you may need to trim up to get the rpm. Temp? Who knows at this point, do you have any idea how long since the impeller was changed?

You probably need some basic info on how things work, try this link.

http://www.mercstuff.com/howdoi.htm

 

[Knot Waiting]

Re: PLEASE HELP> First Boat - First setback

Don,
Thank you for your quick response. I know the water pump was replaced in the spring of this year. As for the impeller... Im not sure. My biggest concern was that if the spline drives on any of the shafts stripped out. Previously had made some mild growling at sharp low speed turns. I just dont want to further damage anything seirous. But I also want to use it. Problem seemed to come an go inconsistantly

 

[Don S]

Re: PLEASE HELP> First Boat - First setback

If you have growling when turning, you need ujoints. May also need a gimbal bearing due to water in the bellows. Which means you need a bellows.
If you had stripped splines, you would be gaining RPM, not loosing it. Plus you wouldn't be moving.
When I mentioned the impeller, that is the inside of the RAW water pump. A marine engine has 2 the other is what is known as circulation pump in marine terminology. Auto terminology it would be known as a water pump. Which are you talking about.
On an Alpha drive, the raw water pump is in the outdrive.

 

[Knot Waiting]

Re: PLEASE HELP> First Boat - First setback

Don,
Thats what concerned me. Is that I am gaining RPM. She was running at about 4000rpm at plane (50mph) instead of her normal 2000. But I also figured it would kind of be a wham bam kind of failure. Like once it stripped it be game over. This high RPM thing kind of surged along as we were cruising. Do you think this is seirous or maybe just a trim issue accompanied by an over sensitive new boat owner? Overheating thing kinda unnerved me. Thank You again.

 

[Fishstick1962]

Re: PLEASE HELP> First Boat - First setback

Don,
Thats what concerned me. Is that I am gaining RPM. She was running at about 4000rpm at plane (50mph) instead of her normal 2000. But I also figured it would kind of be a wham bam kind of failure. Like once it stripped it be game over. This high RPM thing kind of surged along as we were cruising. Do you think this is seirous or maybe just a trim issue accompanied by an over sensitive new boat owner? Overheating thing kinda unnerved me. Thank You again.

Sounds to me like you are trimmed too high.
But it's hard to beleive you rum 50 MPH @ 2000RPM. But anyhow.
1) RPM is up because your prop is coming out of the water.
2)Bout is porposing because you are trimmed too high.
3)Overheat because you are trimmed so high you are not getting enough water in the water ports on the lower unit.
Answer... try trimming down to correct all of these problems. BUTTTT... keep a close watch on your temp, don't want to o'heat the motor.
Good luck!

 

[Don S]

Re: PLEASE HELP> First Boat - First setback

Re: PLEASE HELP> First Boat - First setback

You may also have tach problems, cause I don't think any 23' boat out there will do 50 mph at 2000 rpm.
Many tachs have a switch on the back to set for 4 , 6 and 8 cylinders.
Also, here is a link to a 2001 Mercruiser owners manual, while some of the info isn't going to help, there is a section on trim that may help you understand what is going on with it.
http://www.boatfix.com/merc/Owner/gas/86017101.pdf

Like previously stated, high trim could cause all your problems, even the growling. And if you had it too high, you may have fried you impeller.
You didn't try running it at home without hooking water up to it did you, that would destroy your raw water pump in a hurry.

 

[Knot Waiting]

Re: PLEASE HELP> First Boat - First setback

Thank You guys for all the input, this sport is still somewhat foregin to me so Im glad there are some expeirenced players who are willing to lend some advise
As far as running it out of water, no. I havent owned the boat long enough to get that brave. So it sounds like I may be jumping the gun here by assuming that I have a shaft failure. May be something as simple as over trimmed? It seemed to engage fine from neutral to reverse/foward and get up to plane quickly. I was just fearing the worst, hopefully Im wrong.