"I have a 1998 305 mercruiser engine. I replaced the oil pan and exhaust manifolds and risers 3 years ago due to water in the oil. After that I only ran the engine in the salt water one summer. I winterized it every year. This spring, I ran the engine and noticed gray oil, water mixture. I drained oil, replaced oil filter, replaced oil, and ran engine with ear muffs and hose water connection. After 2 minutes, the oil was contaminated with water again. I checked the exhaust manifold bolts and got about a quarter turn more tightening out of them. My question is do you think the heads are bad, or could it be just blown head gasket, or intake manifold or cracked block? Could something else be bad, like I said, all exhaust manifolds/risers/ gaskets were already replaced 3 years ago. Could they have gone again after only 1 year in salt water?
Last night I check all spark plugs and all were dry, no water spots at all. I did a compression test, ALL cylinders are equally 140 psi. I disconnected the intake hose to the water circulating pump, and disconnected hoses to the exhaust manifold. I had the ear muffs with hose on the outdrive to keep safe the impeller from burning out. I ran the engine for 30 second increments making sure the block or exhaust manifold did not get beyond hot touch to the hand. The oil after 2 changes is now clean. Is there any danger of harming the engine with this approach if I make sure the engine does not overheat?
Before I disassemble the heads and intake manifold, I wanted to be sure what the problem is. I am going to reconnect the intake hose to the water circulating pump, and leave off the exhaust water hose to see if the oil gets contaminated. If it does, can I assume its the intake manifold blown gasket or cracked intake manifold? Could the heads or head gasket still be bad even though the compression test was good and spark plugs are dry?
If the oil does not get contaminated with water, can I then know for sure its the exhaust manifold or exhaust manifold gaskets?
Sorry about the multiple questions. Please let me know, all of your expertise is greatly appreciated. Hope to be boating soon! I will let all know the outcome as I go. Thanks again. Paul