1989 Mercruiser 4.3 LX, Alpha 1 Gen 1 Overheating

[kirkll]

I’ve read though this whole thread and it seems a bit strange that you are more concerned about repainting things than simply replacing the impeller and water pump housing. I think that would be the first thing I did with an overheating issue. It’s a 30 minute job and $40 worth of parts… I would never put an old impeller back in after opening it up.. I’ve had new ones fail in less than 200 hours. Sierra brand. …. You might think about this why you have it apart. It might be as simple as that…. Kirk

 

[PosessionSound26PC]

I’ve read though this whole thread and it seems a bit strange that you are more concerned about repainting things than simply replacing the impeller and water pump housing. I think that would be the first thing I did with an overheating issue. It’s a 30 minute job and $40 worth of parts… I would never put an old impeller back in after opening it up.. I’ve had new ones fail in less than 200 hours. Sierra brand. …. You might think about this why you have it apart. It might be as simple as that…. Kirk

I may have miss-spoken or perhaps you misunderstood... The impeller pump was my first thought, especially after seeing that no water came out of the inlet hose to the engine's water pump. I pulled the lower immediately and I already have two spare pump kits on hand - I have no intention of re-using the old one. I was just trying to say that I didn't find anything obviously wrong with it so it was very unlikely that this was the issue, especially since the engine did not overheat at idle but only downriver a bit at slightly higher idle (no wake zone). I am putting in the new pump tonight. But since I didn't find anything wrong with it, I had to also look at the entire water passage and that means taking off the upper, the lower, and checking the passage through the transom assy, no?

As to cleaning and repainting, I might as well since I had all that torn off, found one failed lower oil seal, had to replace the water pocket seal since I needed to inspect that area, needed a new gasket kit for the upper, and had a torn exhaust bellows - I had to wait for some of those parts to arrive since I didn't have them. Might as well paint while I wait...

Got the upper back on today, maybe lower back on by Wednesday. Boat is not stored at home so it takes me a while to go back and forth and don't have a lot of time. If no overheat after putting it back together, I have no idea what caused it - maybe kelp or plastic bag over inlet? If it overheats with a new pump, it may be the bypass hole in the thermostat housing...

 

[PosessionSound26PC]

I’ve read though this whole thread and it seems a bit strange that you are more concerned about repainting things than simply replacing the impeller and water pump housing. I think that would be the first thing I did with an overheating issue. It’s a 30 minute job and $40 worth of parts… I would never put an old impeller back in after opening it up.. I’ve had new ones fail in less than 200 hours. Sierra brand. …. You might think about this why you have it apart. It might be as simple as that…. Kirk

I should also say that I'm pretty new to boating and know very little about sterndrives in general - I come to this forum to ask for help and I usually get several answers/tips/questions that I have to track down individually. That usually takes time...

 

[PosessionSound26PC]

Update: went to put lower unit back on today, won't go in all the way, about 5/8-3/4" left and feels like hard metal contact like lower shaft hitting beginning of splined opening in upper shaft. In fwd gear. Should I be able to backdrive shaft by turning propeller so I can align splines or do I have to turn shaft by hand little at a time until it lines up? Also, I had to replace lower oil seal in Upper unit and noticed prior to installing it that when it goes over the lower shaft, it pushes the O-ring off. Also noticed there was a design change and Mercruiser deleted the O-ring later and that some people comment about leaving O-ring off because it causes the oil seal spring to pop off... thoughts?

 

[Scott06]

Update: went to put lower unit back on today, won't go in all the way, about 5/8-3/4" left and feels like hard metal contact like lower shaft hitting beginning of splined opening in upper shaft. In fwd gear. Should I be able to backdrive shaft by turning propeller so I can align splines or do I have to turn shaft by hand little at a time until it lines up? Also, I had to replace lower oil seal in Upper unit and noticed prior to installing it that when it goes over the lower shaft, it pushes the O-ring off. Also noticed there was a design change and Mercruiser deleted the O-ring later and that some people comment about leaving O-ring off because it causes the oil seal spring to pop off... thoughts?

Yes merc deleted the o ring on top of veritcal driveshaft so. Do not reinstall it,

i wonder if your water tube is misaligned and thats why you cannot get the two havles back together

 

[nola mike]

Update: went to put lower unit back on today, won't go in all the way, about 5/8-3/4" left and feels like hard metal contact like lower shaft hitting beginning of splined opening in upper shaft. In fwd gear. Should I be able to backdrive shaft by turning propeller so I can align splines or do I have to turn shaft by hand little at a time until it lines up? Also, I had to replace lower oil seal in Upper unit and noticed prior to installing it that when it goes over the lower shaft, it pushes the O-ring off. Also noticed there was a design change and Mercruiser deleted the O-ring later and that some people comment about leaving O-ring off because it causes the oil seal spring to pop off... thoughts?

I leave the o ring off. Turning the prop turns the shaft. Do yourself a favor though and reassemble the drive and then install the complete unit

 

[PosessionSound26PC]

I leave the o ring off. Turning the prop turns the shaft. Do yourself a favor though and reassemble the drive and then install the complete unit

That would make it easier to align the shafts... I may try that.

Scott06, I thought it might be the water tube at first so I tried putting that into the water pocket cover first (in the upper) as well as the way the manual does it but same problem - looks aligned to me... It DOES feel and sound like metal/metal contact to though. The prop didn't want to turn when I tried it but I probably wasn't turning it hard enough.

 

[PosessionSound26PC]

Next to last update (hopefully...):

Got the drive bolted back up and torqued. Hooked up water hose & muffs, ran motor w/ inlet hose to engine's water pump disconnected and observed solid stream of water from new impeller pump - test passed. Reconnected hose and ran motor at idle for 10 minutes - temp gauge held steady at 150F after warming up, water flow at outlets was good. Increased RPM and ran for another 7-8 minutes - temp gauge held steady at 150F throughout. Didn't notice any leaks, and everything seemed well behaved. Putting boat in the water this weekend for a final tryout.

Odd if it was the impeller pump - didn't notice anything wrong with the parts when disassembled... nor any blockage/silt/etc. Fingers crossed it was just a piece of seaweed covering the intakes.

 

[PosessionSound26PC]

Thought the last post was the LAST but...

Took boat out on Sat, Port motor temp was well behaved at dock and in no-wake zone with higher RPMs. Sort of confirms what testing showed in the storage lot with the muffs on (see my last post above this one)

But the trip was cut short by Starboard now having an overheat issue, though slightly different and confirmed again today with more testing at the storage lot and muff/hose.

Not sure if I should start a new thread but here's the problem:

1. Started motors fine at dock, temps stable for some minutes there.
2. Went into no-wake zone at slightly higher RPMs, temps stable again, maybe 10 minutes at this RPM.
3. Needed to slow down approaching dock across water (dropping family off at an island across from launch).
4. Starboard temps increased well above 150, probably around 180 by the time we reached the dock, at roughly idle speed.

This repeated today at the storage lot with muffs and hose:

1. Warmed up and ran motor at higher RPM (1000+)
2. Temps steady at 150F for a good 14-15 minutes.
3. Pulled throttle back to idle to finish test and let it sit there for couple of minutes.
4. Noticed temps starting to go up, kept it at idle for a couple more minutes and sure enough, temps increased to a little over 180F before turning it off.
5. I did notice some steam, or what I think is steam, at the exhaust and at the drain ports at the bottom of the transom assy. Not what I would consider a lot but... Didn't notice much of that on Port...

Any thoughts on this behavior? Why behave and then misbehave? Didn't notice anything unusual on Port...

 

[PosessionSound26PC]

Bump...

 

[Scott06]

Thought the last post was the LAST but...

Took boat out on Sat, Port motor temp was well behaved at dock and in no-wake zone with higher RPMs. Sort of confirms what testing showed in the storage lot with the muffs on (see my last post above this one)

But the trip was cut short by Starboard now having an overheat issue, though slightly different and confirmed again today with more testing at the storage lot and muff/hose.

Not sure if I should start a new thread but here's the problem:

1. Started motors fine at dock, temps stable for some minutes there.
2. Went into no-wake zone at slightly higher RPMs, temps stable again, maybe 10 minutes at this RPM.
3. Needed to slow down approaching dock across water (dropping family off at an island across from launch).
4. Starboard temps increased well above 150, probably around 180 by the time we reached the dock, at roughly idle speed.

This repeated today at the storage lot with muffs and hose:

1. Warmed up and ran motor at higher RPM (1000+)
2. Temps steady at 150F for a good 14-15 minutes.
3. Pulled throttle back to idle to finish test and let it sit there for couple of minutes.
4. Noticed temps starting to go up, kept it at idle for a couple more minutes and sure enough, temps increased to a little over 180F before turning it off.
5. I did notice some steam, or what I think is steam, at the exhaust and at the drain ports at the bottom of the transom assy. Not what I would consider a lot but... Didn't notice much of that on Port...

Any thoughts on this behavior? Why behave and then misbehave? Didn't notice anything unusual on Port...

Verify temp gauge is accurate with a IR gun. What's the history of impeller on this drive are you using OEM parts for impellers and housings?

Verify PS cooler is clear. What is history of thermostat in this engine and does it have the check balls in T on thermostat housing if they dont close can pass too much incoming cold water directly overboard to elbows

 

[PosessionSound26PC]

Verify temp gauge is accurate with a IR gun. What's the history of impeller on this drive are you using OEM parts for impellers and housings?

Verify PS cooler is clear. What is history of thermostat in this engine and does it have the check balls in T on thermostat housing if they dont close can pass too much incoming cold water directly overboard to elbows

Hi Scott - here's a rundown on this motor and drive:

Motor: Recently replaced exhaust risers, flappers, thermostat. Removed, cleaned and repainted exhaust manifolds. It does have check-balls and I re-installed those after cleaning and re-painting thermostat housing - they seemed ok but I wasn't sure how much to tighten... seems like at lower RPM these should have LESS reason to remain open however...

Drive: Recently replaced gimbal bearing. U-bellows and Exhaust bellows looked good. Have never replaced impeller pump but haven't used boat much since bought it from previous owner (a dozen times?). Unsure of last replacement but my impression is he was pretty good about keeping up on maintenance. Impeller pump is obviously my first suspect but was curious if others had seen this specific behavior before because it is odd - doesn't fit with my view of the impeller function.

I'll be away from the boat for a couple of weeks but will check temp w/ IR thermometer (near sensor? I think this one is screwed into the intake manifold...) and verify PS cooler is clear (observed water flow seemed good...).

Thanks.

 

[Scott06]

Hi Scott - here's a rundown on this motor and drive:

Motor: Recently replaced exhaust risers, flappers, thermostat. Removed, cleaned and repainted exhaust manifolds. It does have check-balls and I re-installed those after cleaning and re-painting thermostat housing - they seemed ok but I wasn't sure how much to tighten... seems like at lower RPM these should have LESS reason to remain open however...

Drive: Recently replaced gimbal bearing. U-bellows and Exhaust bellows looked good. Have never replaced impeller pump but haven't used boat much since bought it from previous owner (a dozen times?). Unsure of last replacement but my impression is he was pretty good about keeping up on maintenance. Impeller pump is obviously my first suspect but was curious if others had seen this specific behavior before because it is odd - doesn't fit with my view of the impeller function.

I'll be away from the boat for a couple of weeks but will check temp w/ IR thermometer (near sensor? I think this one is screwed into the intake manifold...) and verify PS cooler is clear (observed water flow seemed good...).

Thanks.

Given your comments on the impeller start there... rule it out as it is the most basic part of the system. Use Oem parts, even “good” aftermarket parts like sierra dont have the lifespan of the oem merc parts. When i had a gen one, i found the sierra impellers lasted half as long as the oem ones that were good for at least 6-7 years

 

[Lou C]

OEM is always best for mission critical parts like impellers & D/S bellows. I do like aftermarket Barr Marine manifolds & elbows.

 

[PosessionSound26PC]

Update: Finally got back to boat and swapped out starboard impeller pump. Does not seem to make a difference - engine still overheats on muffs as described earlier, OK for 10-15mins at idle and higher RPM but overheats when throttle is pulled back to idle. I'm now pretty confident that this is a continuation of my starting and Port overheat issues mentioned earlier (have to open throttle 1/2 way for starboard to start) and that both are due to dirty/gummed up carb(s) that are running lean (Port not as bad). I have Seafoam in the tank but unlikely to work completely. Will get boat in water to confirm this weekend and pull carbs for service when the weather turns.

 

[PosessionSound26PC]

Just wanted to close this issue out - my last post was incorrect. I was relaying what a friend told me he had done at the boat and I misunderstood him - in fact, he had NOT yet replaced the impeller pump and the boat was still overheating, he had just wanted to confirm for himself as he had not been with me when I tested it. It turns out that after we actually replaced the impeller pump, the problem went away. There was visible damage the impeller vanes / some of the material had welded itself to the steel impeller housing. Engine cools just fine now!