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Results 1 to 7 of 7
  1. #1

    Default 1998 305 mercruiser water in oil

    "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

  2. #2
    Join Date
    Jul 2008
    Northboro, Ma, USA

    Default Re: 1998 305 mercruiser water in oil

    Here is my experience relating to water in the oil NOT due to cracked block, heads or bad (no) witerizing.

    In otherwords a boat that had sunk and taken water into the motor.

    Typically if water gets mixed with the oil in a motor due to what ever reason as long as it is not due to a crack in the block or heads or manifolds. It takes as many as 4 - 5 complete oil changes and filters to get rid of 99% of the water.

    The question is where did the water come from.

    If you are 100% sure your motor is free of cracks then you should be OK.

  3. #3

    Default Re: 1998 305 mercruiser water in oil

    I am not sure if I have a crack in block or heads, can you provide diagnosis based on the info I have given? Please give me some guidance! Thanks again

  4. #4
    Join Date
    Jul 2008
    Northboro, Ma, USA

    Default Re: 1998 305 mercruiser water in oil

    If the oil is clear now then the ONLY thing you can do is run it and check the oil.

    You must allow the engine to fully warm up to normal operating temperature.\

    put all the hoses back on, take it to the water, if you can back boat into water and run on trailer allowing normal water system function. let it run till fully warm say 1/2 hour or more.

    check oil during this by pulling the dipstick out. (of course you can shut the engine off to do this) keep checking to see if there is water.

    Dont forget that water will displace the oil so after you run it if the oil level is much higher than when you started then look closer to see if it is water.( of course this is seen after the engine is shut down and allowed to cool off and all oil run back into the pan) So make sure you know exactly how much oil appears on the dip stick before starting the engine test.

  5. #5

    Default Re: 1998 305 mercruiser water in oil

    ok, thanks. I cant back it into the water as its on blocks but I will do the test with the ear muffs/garden hose. Thanks again for your efforts and your time. sincerely Paul

  6. #6
    Join Date
    Jul 2008
    Northboro, Ma, USA

    Default Re: 1998 305 mercruiser water in oil


    if you are going to run it on a garden hose then try not to run full hose pressure. try to adjust it so not much water is spraying away from the ear muffs. That way you are not inducing as much presuure to the system and the motor will warm up more efficiently. Of course do NOT turn the flow to low!!!

  7. #7

    Default Re: 1998 305 mercruiser water in oil

    Ok, thanks for the info. I'll let you know how it goes on Monday. Really a big help.

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