fishingdan
Lieutenant Junior Grade
- Joined
- Feb 12, 2005
- Messages
- 1,045
See explanation below, but how do you know that the exhaust manifold/riser is clogged enough to replace???
1991 4.3lx Alpha One outdrive (rebuilt engine installed in 2000 and relatively low hours since). Boat is a Cobia 19' bowrider and is new to me 1 year ago. Boat has only previously been used in freshwater. Now 70% of time it is run in saltwater.
I have been trouble shooting an overheat problem. I have done the following:
- At end of last season, temp gauge was showing a trend of increasing temps at idle and while running. Gauge would read 180-just under 200.
- As part of maintenance, impeller changed at start of this season. I have done many merc impeller changes and this is now all set. Previous impeller needed replacing, but not the worst that I have seen in the past. No missing pieces, but almost all of the blades and splits from the hub out to the end.
- While the outdrive was off, disconnected the inbound hose from the t-stat housing and back flushed from there out into a bucket. Water flowed freely. No blockages and only some sand collected in the bucket.
- After, temp gauge again read numbers as noted above, but now started to spike when run at higher rpms. Temp would cool down (sometimes to 165 or so) when returned to idle.
- Picked up a infrared temp gun and looked around while on the muffs (forgot to bring it on the water). Once the engine was warmed up, temp at the base of the t-stat housing and around the sender read about 155-165. Temp on the risers was about 150 and manifolds (where they meet riser) was higher.
- Since the boat is relatively new to me. I decided to tear into the t-stat housing (check ball type) and replace the t-stat with a new 140 t-stat. Interior of t-stat house looked more corroded than I expected, but I didn't see any blockages.
- Took the boat to local water and no change in behavior (not that I really expected it). Unfortunately, I forgot the infrared gun to get some temps while in the water rather than on the hose.
Again, not knowing the history of the manifolds/risers. I suspect I have some good corrosion in there. In the boat's maintenance folder, I don't see any history of any change outside of the time the rebuilt engine was installed. I'm assuming that these are 9+ years old. I have no experience with sterndrive setups in saltwater use (all previous boats had outboards), but from what I have been reading, it sounds like I'm do for manifolds/risers.
Tonight, I took off the port side riser. There is some flaking blocking one port and the interior is clearly corroded. However, I was expecting to see more gunk. How do you really know if it is "time" for a change?
Thanks in advance for your thoughts.
Dan
1991 4.3lx Alpha One outdrive (rebuilt engine installed in 2000 and relatively low hours since). Boat is a Cobia 19' bowrider and is new to me 1 year ago. Boat has only previously been used in freshwater. Now 70% of time it is run in saltwater.
I have been trouble shooting an overheat problem. I have done the following:
- At end of last season, temp gauge was showing a trend of increasing temps at idle and while running. Gauge would read 180-just under 200.
- As part of maintenance, impeller changed at start of this season. I have done many merc impeller changes and this is now all set. Previous impeller needed replacing, but not the worst that I have seen in the past. No missing pieces, but almost all of the blades and splits from the hub out to the end.
- While the outdrive was off, disconnected the inbound hose from the t-stat housing and back flushed from there out into a bucket. Water flowed freely. No blockages and only some sand collected in the bucket.
- After, temp gauge again read numbers as noted above, but now started to spike when run at higher rpms. Temp would cool down (sometimes to 165 or so) when returned to idle.
- Picked up a infrared temp gun and looked around while on the muffs (forgot to bring it on the water). Once the engine was warmed up, temp at the base of the t-stat housing and around the sender read about 155-165. Temp on the risers was about 150 and manifolds (where they meet riser) was higher.
- Since the boat is relatively new to me. I decided to tear into the t-stat housing (check ball type) and replace the t-stat with a new 140 t-stat. Interior of t-stat house looked more corroded than I expected, but I didn't see any blockages.
- Took the boat to local water and no change in behavior (not that I really expected it). Unfortunately, I forgot the infrared gun to get some temps while in the water rather than on the hose.
Again, not knowing the history of the manifolds/risers. I suspect I have some good corrosion in there. In the boat's maintenance folder, I don't see any history of any change outside of the time the rebuilt engine was installed. I'm assuming that these are 9+ years old. I have no experience with sterndrive setups in saltwater use (all previous boats had outboards), but from what I have been reading, it sounds like I'm do for manifolds/risers.
Tonight, I took off the port side riser. There is some flaking blocking one port and the interior is clearly corroded. However, I was expecting to see more gunk. How do you really know if it is "time" for a change?
Thanks in advance for your thoughts.
Dan