Hello,
I came across this site by accident and it's great. Here is what I have. My OMC 5.7 exhaust manifolds and risers were replaced 6mos ago after one got blocked and melted the connector at the end of the riser(yes it smoked like crazy and was quite embarassing). I ran the boat one time out of water and all seemed fine. When I took it out, after a short period of time running, it overheated, temp hit about 230. Turns out the impeller completely failed and sent the remains into the power steering cooler. Replaced the impeller, riser gaskets and rubber exhaust connectors (again)and hooked the boat up to the hose. When attempting to start, the starter cranked it over a few times and then it wouldn't crank at all. Both batteries are new and were fully charged overnight. Starter is almost new. Pulled the plugs and water poured out of all 8 cylinders. There is no water in the oil. The compression test resulted in the following: 1.) 75psi 3.)90psi 5.)50psi 7.)75psi 2.)60psi 4.)100psi 6.)70psi 8.)130psi. I still have not performed a wet compression test or leak down. I think at this point I may have a combination of some bad valves and possibly head gaskets. Although this explains the compression, I am not convinced that I could have 2 bad head gaskets putting water in all 8 cylinders. I think the water is coming from the manifolds somehow. They are GLM, very poor quality castings are common on them. I don't know how likely it is that both of them would leak after such a short period of time. Before all of this began the engine ran great but always had to be cranked a lot to start hot or cold even with the choke working properly. Any input would be appreciated. Thanks
I came across this site by accident and it's great. Here is what I have. My OMC 5.7 exhaust manifolds and risers were replaced 6mos ago after one got blocked and melted the connector at the end of the riser(yes it smoked like crazy and was quite embarassing). I ran the boat one time out of water and all seemed fine. When I took it out, after a short period of time running, it overheated, temp hit about 230. Turns out the impeller completely failed and sent the remains into the power steering cooler. Replaced the impeller, riser gaskets and rubber exhaust connectors (again)and hooked the boat up to the hose. When attempting to start, the starter cranked it over a few times and then it wouldn't crank at all. Both batteries are new and were fully charged overnight. Starter is almost new. Pulled the plugs and water poured out of all 8 cylinders. There is no water in the oil. The compression test resulted in the following: 1.) 75psi 3.)90psi 5.)50psi 7.)75psi 2.)60psi 4.)100psi 6.)70psi 8.)130psi. I still have not performed a wet compression test or leak down. I think at this point I may have a combination of some bad valves and possibly head gaskets. Although this explains the compression, I am not convinced that I could have 2 bad head gaskets putting water in all 8 cylinders. I think the water is coming from the manifolds somehow. They are GLM, very poor quality castings are common on them. I don't know how likely it is that both of them would leak after such a short period of time. Before all of this began the engine ran great but always had to be cranked a lot to start hot or cold even with the choke working properly. Any input would be appreciated. Thanks