I've got a 1984 Mariner with an overheating prob. and I apologize in advance for the length of this post.
This motor began to overheat approx. 2 - 3 years after it and the bass boat were purchased new. The buzzer would sound at wot and as soon and as you backed of a little the buzzer would quit. The boat had a new impeller installed every two years since new. This has been a constant and never has an impeller ever come apart.
I brought the boat to a boat mechanic which has done me right in the past and over the next 3-4 years we attempted various fix’s including, lowering the motor on transom, plugging top two intake holes, placing stainless fins over intake holes, rerouting hose from tstats to dump directly out of the cover with 3/8 line from each individual tstat, and replacing impeller pump housing.
In the last 5-6 years the motor has begun to overheat at lower and lower speeds. During the summer months here in Texas it is impossible to even get it on plane with the increase surface water temps.
This lead me to dive back into this project last year and this is what I have done as of late. Removed fins around intake holes, unplugged two top intake holes, raised motor back to original position, rebuilt carbs w/ factory jetting, replaced impeller and housing, replaced plugs but didn't set gap because plug style was flush, replaced poppet valve spring and diaphragm and grommet. Then I cut of a couple coils when problem persisted. This changed nothing if anything it makes it worse.
I also removed power head to replace seal that tube from impeller hosing fits into and removed cleaned and replace water jacket cover above cylinders. The only change that I retained was the straight dump out of the tstats. I did so because they didn't make a difference when we did it and they enable me to closely watch the volume of water coming from t-stats instead of just the pressure as you see with pee hole.
I do not have a pressure gauge or a temp gauge but I did experiment a little the other day with muffs on and this is what I found.
First, with everything together on motor I started and increased throttle until water flow diminished to a trickle from tstats. It is at this point that it usually overheats on lake. This happened at around 12 - 14 hundred rpms. As soon as water flow disappeared I went to idle and approx 8 - 10 seconds later the water began flowing out of t-stats again.
Next, I removed outer cover to poppet valve and replaced bolts with shorter ones. This enables me to watch poppet valve operation because of the now exposed diaphragm. Motor was started and at 12 - 14 hundred rpms water flow again diminished from tstats. At exactly the same time the poppet valve began releasing water. Once again the motor was brought back to idle and approx 10 secs later water began flowing from tstats.
Finally, I removed poppet valve assembly completely and plugged hole using a carved down stopper for transom. I again started motor and increased rpms waiting for water to stop flowing from tstats. It never did. Without the poppet valve the motor ran as it should at least with muffs on.
I have done compression tests on this motor in the past and went ahead and did another one after this little test. 125lbs on every cylinder just like it always does.
There is no corrosion in the water passages that I can see.
This leads me to believe that I need a stronger poppet valve spring. Could this be the problem that has nagged me for over 20 years? Is there any way exhaust gasses could be escaping and pressurizing the water passages causing valve to open.
Any help from you guys would be great. I have almost broke down and bought a new motor several times. I also know that I need a pressure gauge and a temp gauge from reading the other posts. Let me know best brand and place to get if you can.
Thanks for any input at all, even if only to criticize my longer than normal post.
This motor began to overheat approx. 2 - 3 years after it and the bass boat were purchased new. The buzzer would sound at wot and as soon and as you backed of a little the buzzer would quit. The boat had a new impeller installed every two years since new. This has been a constant and never has an impeller ever come apart.
I brought the boat to a boat mechanic which has done me right in the past and over the next 3-4 years we attempted various fix’s including, lowering the motor on transom, plugging top two intake holes, placing stainless fins over intake holes, rerouting hose from tstats to dump directly out of the cover with 3/8 line from each individual tstat, and replacing impeller pump housing.
In the last 5-6 years the motor has begun to overheat at lower and lower speeds. During the summer months here in Texas it is impossible to even get it on plane with the increase surface water temps.
This lead me to dive back into this project last year and this is what I have done as of late. Removed fins around intake holes, unplugged two top intake holes, raised motor back to original position, rebuilt carbs w/ factory jetting, replaced impeller and housing, replaced plugs but didn't set gap because plug style was flush, replaced poppet valve spring and diaphragm and grommet. Then I cut of a couple coils when problem persisted. This changed nothing if anything it makes it worse.
I also removed power head to replace seal that tube from impeller hosing fits into and removed cleaned and replace water jacket cover above cylinders. The only change that I retained was the straight dump out of the tstats. I did so because they didn't make a difference when we did it and they enable me to closely watch the volume of water coming from t-stats instead of just the pressure as you see with pee hole.
I do not have a pressure gauge or a temp gauge but I did experiment a little the other day with muffs on and this is what I found.
First, with everything together on motor I started and increased throttle until water flow diminished to a trickle from tstats. It is at this point that it usually overheats on lake. This happened at around 12 - 14 hundred rpms. As soon as water flow disappeared I went to idle and approx 8 - 10 seconds later the water began flowing out of t-stats again.
Next, I removed outer cover to poppet valve and replaced bolts with shorter ones. This enables me to watch poppet valve operation because of the now exposed diaphragm. Motor was started and at 12 - 14 hundred rpms water flow again diminished from tstats. At exactly the same time the poppet valve began releasing water. Once again the motor was brought back to idle and approx 10 secs later water began flowing from tstats.
Finally, I removed poppet valve assembly completely and plugged hole using a carved down stopper for transom. I again started motor and increased rpms waiting for water to stop flowing from tstats. It never did. Without the poppet valve the motor ran as it should at least with muffs on.
I have done compression tests on this motor in the past and went ahead and did another one after this little test. 125lbs on every cylinder just like it always does.
There is no corrosion in the water passages that I can see.
This leads me to believe that I need a stronger poppet valve spring. Could this be the problem that has nagged me for over 20 years? Is there any way exhaust gasses could be escaping and pressurizing the water passages causing valve to open.
Any help from you guys would be great. I have almost broke down and bought a new motor several times. I also know that I need a pressure gauge and a temp gauge from reading the other posts. Let me know best brand and place to get if you can.
Thanks for any input at all, even if only to criticize my longer than normal post.
