Questions about a 1989 Johnson GT 150 VRO

[85stratosman]

I am checking out this 89 johnson GT 150 VRO to put on my 18ft stratos bass boat because I am over rated right now with the Mariner 175 and can not fish tournaments. The questions I have are as follow, I run a compression check and all cylinders except for #5 checked out right at 100 and #5 checked out at 90, I read on here that for those motors that compression is good but compared to my Mariner having 120 on all cylinders this makes me kinda skeptical. The motor has sat up for 5 years and not been run it took me about ten minutes hooking good pre mixed gas and oil up to the motor and cleaning the plugs and a good battery to get it to fire up. It sounds strong and has a little miss at idle. Now the cooling system is set up different from the Mariner which I am use to. The johnsons cooling system just has a nipple coming out of the block straight to the pee hole I cleaned the dirt dobbers out and to my surprise the impeller still had a strong pump for sitting up so long, but my concern on that is with the muffs on the water coming out of the pee tube is still cold it never warms up like on the mariner. Is this normal for the cooling and is the compression really ok. Any comments would be greatly appreciated. Thanks

 

[Ken G]

Re: Questions about a 1989 Johnson GT 150 VRO

I think I've read on here somewhere that the Johnrude crossflow V-6s have lower compression then some other motors. That is a good thing since I found mine to be 95-96 across the board last week on my '87 150.

I have a 1970 Merc 135 hp inline 6 that sat for 10 years and checks out around 145 psi.

 

[diver_down]

Re: Questions about a 1989 Johnson GT 150 VRO

these motors have a factory compression around 5 or 6 to 1 so it has good compression (mine has about 85 across the board, ran like a champ). change impeller (drop lower unit, pump is on the shaft, you need to disconnect shift linkage in front of the block, kind of under it - a pain in the but, but otherwise quite simple). change thermostats at the same time, they might be stuck, or at least take out and clean. you will need new gaskets. CLEAN THE CARBS or you will be asking for rebuild advice really soon. do a link and sinc, set idle and WOT advance to specs. run a decarb and and change lower unit oil, check for water or metal shaves in it.
the water coming out of the pee-hose is usually cold unless the motor is under load, on mine it's barely different than the input water (1985).
it would be nice to be able to test it on the water but at least let it run until it's warmed up on muffs, check voltage coming out of the regulator (about 13V DC) as well as voltage coming out of the stator winding (AC current, should be around 20V at idle). Mine fried the stator soon after i got it - not a cheap thingy.

 

[rshiver]

Re: Questions about a 1989 Johnson GT 150 VRO

"these motors have a factory compression around 5 or 6 to 1 so it has good compression (mine has about 85 across the board, ran like a champ). "

Would those compression numbers apply to an 89 GT 200 also?

Thanks

 

[diver_down]

Re: Questions about a 1989 Johnson GT 150 VRO

i've seen a chart somewhere on a website recently, it had to do with the recommended octane rating for outboards. if my memory is correct all the V6 crossflows were in the same category - 5 to 6 / 1 compression ratio. if i manage to find it again i'll post a link, however i found the link initially on this forum so it's somewhere.
by the way, there was LOTS of good info in there.

 

[diver_down]

Re: Questions about a 1989 Johnson GT 150 VRO

http://members.iinet.net.au/~pauldawson/DETON-PWD-94.pdf
look at the chart on page 17

 

[rshiver]

Re: Questions about a 1989 Johnson GT 150 VRO

Thanks for the info Diver, I feel better about the cylinder pressures now. I have 90 across the board +/- 1 or 2 psi. Now if I can figure out why I'm only getting a spark on one cylinder I'll be a happy puppy, but thats for another thread. Thanks again

 

[Jeff_G]

Re: Questions about a 1989 Johnson GT 150 VRO

I am checking out this 89 johnson GT 150 VRO to put on my 18ft stratos bass boat because I am over rated right now with the Mariner 175 and can not fish tournaments. The questions I have are as follow, I run a compression check and all cylinders except for #5 checked out right at 100 and #5 checked out at 90, I read on here that for those motors that compression is good but compared to my Mariner having 120 on all cylinders this makes me kinda skeptical. The motor has sat up for 5 years and not been run it took me about ten minutes hooking good pre mixed gas and oil up to the motor and cleaning the plugs and a good battery to get it to fire up. It sounds strong and has a little miss at idle. Now the cooling system is set up different from the Mariner which I am use to. The johnsons cooling system just has a nipple coming out of the block straight to the pee hole I cleaned the dirt dobbers out and to my surprise the impeller still had a strong pump for sitting up so long, but my concern on that is with the muffs on the water coming out of the pee tube is still cold it never warms up like on the mariner. Is this normal for the cooling and is the compression really ok. Any comments would be greatly appreciated. Thanks

Change your engine cowl

 

[emdsapmgr]

Re: Questions about a 1989 Johnson GT 150 VRO

The OMC's do run lower compression than the Mercs. The thing to look for is even compression on each side, and you have one cyl. at 90. Usually 10% difference is acceptable-and that cyl is right there. You may find that using some Bombardier Engine Tuner will bring that cyl up somewhat. Pull the spark plug and see if you can see anything inside-esp check for scuffing on that cyl's wall. OMC's do have strong, reliable impellers-a strong design feature vs the Mercs.