Overkill82k5
Petty Officer 3rd Class
- Joined
- Jul 29, 2009
- Messages
- 78
I finally have everything setup and finished from a complete rebuild of a Merc 5.7 with an Alpha 1. I have only been able to test run the engine in the driveway on muffs.
The engine was punched 40 over and rebuilt from a catastrophic water jacket failure (I think) in one of the heads. Previous to me purchasing the boat, with the blown motor, the #2 exhaust valve shattered and sent shrapnel throughout the motor and ate up 5 of the 8 pistons and cylinders. I assume cold water from a water jacket failure in the head, mixed with a very hot exhaust valve and crystalized it, allowing it to shatter like glass. Engine was previously punched 30 over. I added 10 more to clean up the cylinders and also to fit a set of pistons I already had on hand (+ 40's).
Engine went back together nicely, with the exception of the head water jacket issue. I didnt know about the leaks until I put the leaky heads back on and ended up with water in... well, everything internal. I replaced the heads and test ran the motor on a test stand. Motor runs awesome, sounds awesome and seems to be really solid.
Now the question part... Once I got the motor installed in the boat, I did some testing on the muffs in the driveway. Everything went very well with the exception of running temps. At idle, the temp rises normally to midway on the guage. After that the temp keeps edging upward until it hits the redline (5 to 8 minutes after reaching what should be normal operating temp). I don't know if it is actually overheating or it's the guage. I shut it down as soon as it touched the red line on the guage since I don't want to risk damage to a new motor.
I put a new water pump kit in the leg, the old impeller was desintegrated. Cleaned all the old impeller bits out of the pickup screen and back flushed from the tstat housing down thru the upper outdrive. Water seemed to flow really well from hose pressure. I replaced all the bellows and the water hose that goes from the outdrive to, and through, the transom shield. I have unnecessarily replaced the water circ pump on the motor also since that was the only piece left that wasn't new. This did not cure my creeping temp problem.
When replacing the outdrive pickup hose I noticed that the metal tube going thru the transom seemed really small. It seemed strange to me that the outdrive water pump could pump enough pressure to allow significant flow through this bottleneck to cool a 350 CI motor. It looks like an ID of around a half inch. Once inside the transom, an adapter takes that 1/2"-ish line and opens it up to a 1.25" or 1.5" hose that goes to the circ pump.
This engine and outdrive has been replaced previous to me purchasing it and I am wondering if something was amiss since the replacement. I am still troubleshooting the creeping temp issue and I may have an issue with the motor itself or it could be something as simple as the temp guage, sending unit or a corroded wire adding extra resistance along the way. I just wanted to gather a concensus before digging into the electrical, or engine internal side of things. If the water tube size is normal then I can focus my efforts elsewhere.
Also, the water tube seems to have a fitting on it that makes it look like it can be removed and replaced. IF replacement is an option, would/could there be larger tubes available to switch to in order to soften this bottleneck? I have even contemplated having a custom one made if necessary, but if this isn't the likely culprit I dont want to waste my time and resources. While running on the muffs the water flow out the back of the boat seems to be about .5 to .75 of the flow that my 3.0 I/O on my other boat does on the same muffs/hose.
Thanks, and sorry for the mini novel. I try to answer questions before they are asked.
The engine was punched 40 over and rebuilt from a catastrophic water jacket failure (I think) in one of the heads. Previous to me purchasing the boat, with the blown motor, the #2 exhaust valve shattered and sent shrapnel throughout the motor and ate up 5 of the 8 pistons and cylinders. I assume cold water from a water jacket failure in the head, mixed with a very hot exhaust valve and crystalized it, allowing it to shatter like glass. Engine was previously punched 30 over. I added 10 more to clean up the cylinders and also to fit a set of pistons I already had on hand (+ 40's).
Engine went back together nicely, with the exception of the head water jacket issue. I didnt know about the leaks until I put the leaky heads back on and ended up with water in... well, everything internal. I replaced the heads and test ran the motor on a test stand. Motor runs awesome, sounds awesome and seems to be really solid.
Now the question part... Once I got the motor installed in the boat, I did some testing on the muffs in the driveway. Everything went very well with the exception of running temps. At idle, the temp rises normally to midway on the guage. After that the temp keeps edging upward until it hits the redline (5 to 8 minutes after reaching what should be normal operating temp). I don't know if it is actually overheating or it's the guage. I shut it down as soon as it touched the red line on the guage since I don't want to risk damage to a new motor.
I put a new water pump kit in the leg, the old impeller was desintegrated. Cleaned all the old impeller bits out of the pickup screen and back flushed from the tstat housing down thru the upper outdrive. Water seemed to flow really well from hose pressure. I replaced all the bellows and the water hose that goes from the outdrive to, and through, the transom shield. I have unnecessarily replaced the water circ pump on the motor also since that was the only piece left that wasn't new. This did not cure my creeping temp problem.
When replacing the outdrive pickup hose I noticed that the metal tube going thru the transom seemed really small. It seemed strange to me that the outdrive water pump could pump enough pressure to allow significant flow through this bottleneck to cool a 350 CI motor. It looks like an ID of around a half inch. Once inside the transom, an adapter takes that 1/2"-ish line and opens it up to a 1.25" or 1.5" hose that goes to the circ pump.
This engine and outdrive has been replaced previous to me purchasing it and I am wondering if something was amiss since the replacement. I am still troubleshooting the creeping temp issue and I may have an issue with the motor itself or it could be something as simple as the temp guage, sending unit or a corroded wire adding extra resistance along the way. I just wanted to gather a concensus before digging into the electrical, or engine internal side of things. If the water tube size is normal then I can focus my efforts elsewhere.
Also, the water tube seems to have a fitting on it that makes it look like it can be removed and replaced. IF replacement is an option, would/could there be larger tubes available to switch to in order to soften this bottleneck? I have even contemplated having a custom one made if necessary, but if this isn't the likely culprit I dont want to waste my time and resources. While running on the muffs the water flow out the back of the boat seems to be about .5 to .75 of the flow that my 3.0 I/O on my other boat does on the same muffs/hose.
Thanks, and sorry for the mini novel. I try to answer questions before they are asked.
