fishingdan
Lieutenant Junior Grade
- Joined
- Feb 12, 2005
- Messages
- 1,045
I'm tracking down a blockage on an overheating 1991 4.3LX Alpha. Everything is good up to the circulating pump. I'm still looking for the "aha! that's IT moment". I have had the boat one year. It was previously a freshwater only boat. A rebuilt engine was installed in 2001 and it is a good runner.
At the end of last season, the engine was starting to run warmer per the dash gauge (180-190 per the gauge). This spring, I replaced the water pump impeller and on first outing, temp was still high. IR temp gun showed higher than desired temps (~170 at the t-stat housing base). After using it and seeing the temps slowly climb, I figured that the exhaust manifolds/elbows were beyond their useful like especially since I started using it in saltwater (flushing at times after an outing, but not every time...). While I was waiting for the new manifolds/elbows to arrive, I decided to inspect the t-stat housing. While I was in there, I checked the hoses, the housing and changed the t-stat.
I had a scheduled vacation and decided to take the boat to see if there was any change. There wasn't except that it now started to overheat higher when running the boat. Previously, it would run up to about 190ish on the gauge and then drop a bit at a high idle. Now, it go right past 190ish on the gauge where I would shut it down.
This is what I have done to date. I have a lot of experience with merc outboards (at least makes changing the waterpump easy), but not as much on sterndrives (especially with saltwater use). I love tinkering and learning about the power plants. I love to know the first-hand history of the engine's typical failure/maintenance points. As you can see, I have replaced some parts based on educated guesses and my reading here. In the end, if I replaced something a little early, I'm ok with that because I now have some peace of mind with the first hand knowledge that has been gained.
- raw water pump in the outdrive is new at the beginning of the season and is ok. Pump pushed good volume of water up to the t-stat housing roughly per the spec that I have seen referenced on this site. The old impeller was worn and the veins were split laterally with no apparent missing pieces.
- Back flushed through hose leading to power steering cooler through outdrive (with lower unit removed). Some sand in the bucket, but no indication of any blockage.
- I installed new manifolds/elbows (didn't know the history of them and so I decided to replace them). The old exhaust elbows had some scale and some blockage.
- Again, not knowing the history of the t-stat, I replaced it with the correct 140 t-stat while inspecting the t-stat housing (check ball style) and related hoses.
- Not knowing the history of the circulation pump, I pulled it to inspect. No apparent leakage or noise to indicate bad bearings/seals before removal. Nothing unusual found after removal. Bearings seem fine and impeller looks good. Other than the bearings/seal, is there anything else that can go wrong with these?
- Oil looks fine
While I have the circulating pump off, i thought I would take the opportunity to black flush the block and confirm that water will flow freely through there. Is there any basic way to do this?
Any other thoughts?
thanks
At the end of last season, the engine was starting to run warmer per the dash gauge (180-190 per the gauge). This spring, I replaced the water pump impeller and on first outing, temp was still high. IR temp gun showed higher than desired temps (~170 at the t-stat housing base). After using it and seeing the temps slowly climb, I figured that the exhaust manifolds/elbows were beyond their useful like especially since I started using it in saltwater (flushing at times after an outing, but not every time...). While I was waiting for the new manifolds/elbows to arrive, I decided to inspect the t-stat housing. While I was in there, I checked the hoses, the housing and changed the t-stat.
I had a scheduled vacation and decided to take the boat to see if there was any change. There wasn't except that it now started to overheat higher when running the boat. Previously, it would run up to about 190ish on the gauge and then drop a bit at a high idle. Now, it go right past 190ish on the gauge where I would shut it down.
This is what I have done to date. I have a lot of experience with merc outboards (at least makes changing the waterpump easy), but not as much on sterndrives (especially with saltwater use). I love tinkering and learning about the power plants. I love to know the first-hand history of the engine's typical failure/maintenance points. As you can see, I have replaced some parts based on educated guesses and my reading here. In the end, if I replaced something a little early, I'm ok with that because I now have some peace of mind with the first hand knowledge that has been gained.
- raw water pump in the outdrive is new at the beginning of the season and is ok. Pump pushed good volume of water up to the t-stat housing roughly per the spec that I have seen referenced on this site. The old impeller was worn and the veins were split laterally with no apparent missing pieces.
- Back flushed through hose leading to power steering cooler through outdrive (with lower unit removed). Some sand in the bucket, but no indication of any blockage.
- I installed new manifolds/elbows (didn't know the history of them and so I decided to replace them). The old exhaust elbows had some scale and some blockage.
- Again, not knowing the history of the t-stat, I replaced it with the correct 140 t-stat while inspecting the t-stat housing (check ball style) and related hoses.
- Not knowing the history of the circulation pump, I pulled it to inspect. No apparent leakage or noise to indicate bad bearings/seals before removal. Nothing unusual found after removal. Bearings seem fine and impeller looks good. Other than the bearings/seal, is there anything else that can go wrong with these?
- Oil looks fine
While I have the circulating pump off, i thought I would take the opportunity to black flush the block and confirm that water will flow freely through there. Is there any basic way to do this?
Any other thoughts?
thanks