Today when I got out on the water and went to start the engine, it sounded good for a second but didn't turn over.  Turned the key again and it just grumbled and let out a little whiney noise.  Never got it to start and it just kept growling more weakly when ever I turned the key.  Whenever the motor would growl, the depthfinder would shut off.  Both are connected to the cranking battery.  I thought the cranking battery was fully charged but took it home to charge and it took a while. Any ideas of other possible culprits?

Well, let's see if we can break the growls, grumbles and whiney noises down into understandable motor terms.

You say it sounded good but didn't turn over.  If a motor is not spinning over, it's not cranking.  If it cranking over but won't start, then it won't run/start.

Your depth finders cutting off means the battery is being pulled too much.   To check it, you need a volt meter.  Connect the meter across the lead post or mounting studs on the battery and crank the motor.  Voltage should not drop below about 11.5 volts.  If it's droping below this, you're battery is bad or not fully charged.   If it's holding voltage, move the meter leads and connect them to the battery cables themselves and crank it again.  It the voltage drops way down then, you have bad/dirty connections at the battery.  If it's holding voltage at the cables, then you need to check the voltage at the solenoid and starter.   

I have a feeling you're battery is junk.

Yep, never cranked. I got the battery fully charged so I might try it out when I can get some muffs. Will muffs work with the GT 150's water inakes? I hear they don't work on some motors.

And also, while we're at it, since you seem to know a lot about OMC motors, is 1-2 MPG about average fora GT 150 on an 18 glass boat?  I know measuring MPG is not usually done on boats and any fuel consumption measurement is hard, but does that sound right?

Sounds like a battery issue or something in the starting system.

Tight Lines

Pa Angler

charge your battery or hook a new battery to the engine and that should solve your problem.

Haven't you heard why they used the name GT150. GT stands for Gas Thirsty. Those old cross-flow are not known for their fuel economy.

A good prop on a properly setup boat and keeping your cruising rpm below 4,500 will help a lot.  When I had my Stratos 285 Pro with a GT150, it would get about 3.5mpg cruising and about half that at WOT.

If you have the standard lower unit, yes, the muffs will work on it.

You really don't need muffs to check the battery. You only need to try and crank it for a few seconds to see if it's going to crank over or pull the battery down. If it cold starts that easy, it will be the first one I've seen that does.

Sounds like W2S got it diagnosed to a T but just thought I'd offer something else I've heard more than once from GT owners having difficulty starting at the ramp.

I'm not an outboard expert, I have a newer OMC 150 but a friend had a GT 150.  Dealer told him not to tilt it too much after priming cause those motors were notorious for dumping fuel back out of the intake thru carbs according to him and resulted in starting problems due to lack of fuel.  Had another GT owner relay the same story.  May be something to be aware of at the ramp when launching.

With the GT motors, they start a lot easier if you have the top of the motor level.

If it cold starts that easy, it will be the first one I've seen that does.

No kidding. Every Johhny/Rude I ever had was very hard to start cold. The GT150 I had was bulletproof once it started.