Does this 1987 Johnson GT 150 sound okay to you? Have a video here...

[spencerkechi]

We bought a 1995 deck/pontoon boat that came with a 1987 Johnson GT 150. We were told the motor was a 1995, but after looking at the model number, we see it is not. We took the seller's word for it at the time and had an independent boat mechanic tell us the motor seems fine (compression good). We are not so sure. We have not had the boat on the water yet and are trying to get it ready for a trip in early October. We told the mechanic it appeared to be running rough, he said it was normal and would perform well under load.

Something just doesn't sound right, even though it starts up fine. Given that we are not familiar with outboards, we thought we might if anybody would be willing to watch this short youtube video of the motor running and help us determine whether or not we need to take it to a new mechanic first before going to the lake. And we appreciate your insight! https://youtu.be/ZV1YB-IXkUE

 

[Bosunsmate]

Seems alright to me. Hard to know until you do put it under load. If you have the compression readings it would be handy if you posted them.
You could also check the gear oil. Dont undo the philips screw on the lower leg though as that will create a whole new world of outboard mechanic trouble.

You should also run it for a while on that hose and check the temperature of the heads, You should be able to keep your hand on them for at least ten seconds. Anymore and you might have cooling issues which would be the most likely problem that would ruin your planned trip away

 

[oldboat1]

I would get the impeller changed out before taking it out -- and strongly recommend against revving when on the hose.

 

[interalian]

These motors pop and snarl like mad without the backpressure of being in water. Sounds like any larger one idling on muffs to my ears.

 

[emdsapmgr]

Actually, for a crossflow, this one runs very smooth. I am in favor of changing the impeller prior to your first launch. That way you know you are starting out with a new pump on your maiden voyage.

 

[jimmbo]

The 90 degree crossflow V6 will always have a uneven sound to it as it doesn't fire every 60 degrees of crankshaft rotation. It fires at 90-30-90-30-90-30 degree intervals.

 

[racerone]

The philips screw on that lower unit is there to prevent a bearing from moving due to oil pressure in the bearing.------That screw should be left alone , but is not a disaster when taken out.

 

[spencerkechi]

Thanks, everyone, really appreciate it. I cannot remember the exact compression on each cylinder, but I remember they were all right around 80 lbs. We had to do some research on this site about those readings because we thought they sounded really low for a cylinder, but according to what we read here, we understand it is normal for this motor.

Three more questions, everyone, and we do appreciate your help on this!

1. Is there some diagram or help video that will show us how to replace the impeller? We have very little experience with an outboard motor. I think it is good advice. We thought the water stream seemed a bit weak in the video.
2. Does anybody know which impeller we need to buy and where a good place is to buy one?
3. I am a bit worried about this lower unit screw you guys are talking about. The only screw I have messed with was to change the lower unit oil. Given that it is a flat head, I presume I have not jacked something else up. Is this phillips screw on the port side?

thanks, everyone, you have been very helpful!

 

[interalian]

Lots of YouTube clips on changing impellers - just Google.
iBoats (this site) has the pump parts you need.
There are two slotted screws for the lower unit oil. Both are removed to drain, then you refill by pumping oil into the bottom one until it comes out the top. Then put the top screw in, then quickly pull the pump hose out of the bottom and put the bottom screw in. Use new crush gaskets.

 

[spencerkechi]

Okay, I think I have handle on the lower unit grease and we did buy new gaskets for it when we changed it. The videos I am seeing on the impeller change, so far, appear to be universal in nature. Does anybody know if it is necessary to shift the boat into reverse and detach the shift shaft to remove the lower unit on this 1987 Johnson GT 150?

 

[Bosunsmate]

oil, not grease by the way, grease is only for the very old units

 

[David Young]

Sounds good to me. Change the impeller and lower unit gear oil then take it for a trial run to see how it does. With this Forum, factory service manual and youtube video's, I have done all my repairs and maintenance myself saving 100's of dollars