jmccaskamite
Recruit
- Joined
- Oct 23, 2012
- Messages
- 3
Hello,
I need some advice from the iboats community because I am completely stumped!
I have a GM350 / Mercruiser 260, Alpha One, closed cooled system in a 1979 Century 26ft. The exhaust manifolds are the log type with 180 deg exit exhaust elbows. The problem I am having is the engine overheats when run at 3000 RPM or above. It runs at normal operating temp (175-180) at 2800 RPM but will start to overheat when the RPM is raised to 3000 or above. It has maintained it's operating temp at higher RPM until recently. Here is some background to the problem:
Over the summer, everything was operating as it should after I made these changes:
Installed -
New heat exchanger (san juan engineering)
New heat exchanger cap
New thermostat (175 deg)
New temperature sending unit
New freshwater pump
New hoses
New water pump
New valves and guides in the heads and head gaskets
Overall state of motor-
Good compression
Good vacuum
Runs well
The start of the problem:
As of recently, after engine warmed up, it would start to smoke out of the exhaust. The smoke was white and smelled of coolant.
I replaced the exhaust elbow gaskets and reinstalled the elbows. The smoke went away and the new overheating problem started.
I noticed that the elbows were corroded when I had them removed so I removed them again and replaced with new exhaust elbows. I also needed to replace the metal plates that go in between the exhaust gaskets. The new ones from the parts counter looked identical except for a small pin hole that would be covered by the gaskets upon istall. I installed the new parts and I am still having the problem.
I figured that there may be a blockage somewhere so I drained the coolant by opening the petcocks on both sides of the engine block. I was hoping that any debris would find it's way out of the system. Once all of the coolant was drained I proceeded to fill the system with new coolant. I followed the steps to properly refilling in the Mercruiser repair manual on the Boatinfo site. I filled the coolant to where I could see it in the heat exchanger and started the engine. I ran it at a fast idle (1600) and expected the coolant to drop in level as the thermostat opened at operating temp. Before the engine even got to heat up, the coolant was just spilling out of the heat exchanger! I got a large funnel that seals to the heat excahnger filler neck to allow bubbles etc to come out without spilling the coolant and the large funnel fills up with coolant! As soon as I shut it down it slowly starts to return to back in to the system. Does this mean there is a blockage or should I have started the engine first with no coolant and immediately started filling with coolant while running?
Possible contributors to the issue:
I am having engagement issues with the reverse function on the sterndrive simultaneous to this problem. Could this have anything to do with high RPM temp rises?
I hope someone has the patience to read through these steps and offer some advice. I am missing some good fishing days with this problem!!!
Thanks.
I need some advice from the iboats community because I am completely stumped!
I have a GM350 / Mercruiser 260, Alpha One, closed cooled system in a 1979 Century 26ft. The exhaust manifolds are the log type with 180 deg exit exhaust elbows. The problem I am having is the engine overheats when run at 3000 RPM or above. It runs at normal operating temp (175-180) at 2800 RPM but will start to overheat when the RPM is raised to 3000 or above. It has maintained it's operating temp at higher RPM until recently. Here is some background to the problem:
Over the summer, everything was operating as it should after I made these changes:
Installed -
New heat exchanger (san juan engineering)
New heat exchanger cap
New thermostat (175 deg)
New temperature sending unit
New freshwater pump
New hoses
New water pump
New valves and guides in the heads and head gaskets
Overall state of motor-
Good compression
Good vacuum
Runs well
The start of the problem:
As of recently, after engine warmed up, it would start to smoke out of the exhaust. The smoke was white and smelled of coolant.
I replaced the exhaust elbow gaskets and reinstalled the elbows. The smoke went away and the new overheating problem started.
I noticed that the elbows were corroded when I had them removed so I removed them again and replaced with new exhaust elbows. I also needed to replace the metal plates that go in between the exhaust gaskets. The new ones from the parts counter looked identical except for a small pin hole that would be covered by the gaskets upon istall. I installed the new parts and I am still having the problem.
I figured that there may be a blockage somewhere so I drained the coolant by opening the petcocks on both sides of the engine block. I was hoping that any debris would find it's way out of the system. Once all of the coolant was drained I proceeded to fill the system with new coolant. I followed the steps to properly refilling in the Mercruiser repair manual on the Boatinfo site. I filled the coolant to where I could see it in the heat exchanger and started the engine. I ran it at a fast idle (1600) and expected the coolant to drop in level as the thermostat opened at operating temp. Before the engine even got to heat up, the coolant was just spilling out of the heat exchanger! I got a large funnel that seals to the heat excahnger filler neck to allow bubbles etc to come out without spilling the coolant and the large funnel fills up with coolant! As soon as I shut it down it slowly starts to return to back in to the system. Does this mean there is a blockage or should I have started the engine first with no coolant and immediately started filling with coolant while running?
Possible contributors to the issue:
I am having engagement issues with the reverse function on the sterndrive simultaneous to this problem. Could this have anything to do with high RPM temp rises?
I hope someone has the patience to read through these steps and offer some advice. I am missing some good fishing days with this problem!!!
Thanks.
