vanman59
Member
- Sep 13, 2015
- 51
- Boat Info
- 30' 1989 Sea Ray Weekender
1992 Dodge W250 Cummins W/auto trans
- Engines
- Twin Merc 454s
1989 300 Weekender, 454 mercruiser, closed cooling system. started overheating last year. Here's what I've done:
1. found the left bank manifold had a whole in it at the #5 cylinder due to a leak between the riser and gasket, leaking and dripping salt water into the manifold directly into the #5 exhaust. Good thing the bottom of the exhaust port in the manifold was lower than the valve seat. This let salt water sit in the manifold until it rusted a hole in it. I replaced the left bank manifold only. I broke two bolts off in the head but luckily they stuck out enough to use break free and tap with a hammer and vice grips to remove the broken bolts. I am not to keen on replacing the outboard manifold just yet (bolts are very tight).
2. Replaced raw water impeller and housing. The impeller was good, impeller was not missing any fins and was still very pliable. Still overheated.
3. Replaced the circulating pump and thermostat with marine bi-directional pump and 145 degree thermostat. still over heating under load.
Here is where I am today: when we were replacing the engine circulating pump I noticed the coolant was black but didn't think anything about it. I was removing the right bank riser and noticed corrosion on the top of the manifold where the riser bolts to it. I took the riser off and it seems that maybe there could have been a leak between the manifold and gasket that let exhaust gas into the fresh water cooling system. My reasoning behind this hypothesis is the inside of the manifold is sooty due to running a little rich and it hit me that the coolant is black, and the manifold looks like it has been getting corroded due to a possible leak at the riser/manifold. Any suggestions would be appreciated.
1. found the left bank manifold had a whole in it at the #5 cylinder due to a leak between the riser and gasket, leaking and dripping salt water into the manifold directly into the #5 exhaust. Good thing the bottom of the exhaust port in the manifold was lower than the valve seat. This let salt water sit in the manifold until it rusted a hole in it. I replaced the left bank manifold only. I broke two bolts off in the head but luckily they stuck out enough to use break free and tap with a hammer and vice grips to remove the broken bolts. I am not to keen on replacing the outboard manifold just yet (bolts are very tight).
2. Replaced raw water impeller and housing. The impeller was good, impeller was not missing any fins and was still very pliable. Still overheated.
3. Replaced the circulating pump and thermostat with marine bi-directional pump and 145 degree thermostat. still over heating under load.
Here is where I am today: when we were replacing the engine circulating pump I noticed the coolant was black but didn't think anything about it. I was removing the right bank riser and noticed corrosion on the top of the manifold where the riser bolts to it. I took the riser off and it seems that maybe there could have been a leak between the manifold and gasket that let exhaust gas into the fresh water cooling system. My reasoning behind this hypothesis is the inside of the manifold is sooty due to running a little rich and it hit me that the coolant is black, and the manifold looks like it has been getting corroded due to a possible leak at the riser/manifold. Any suggestions would be appreciated.