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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10806
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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i got 305 mercruser 1990 water goes in the engine oil

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i got 305 mercruser 1990 water goes in the engine oil
If you have an oil cooler that can cause it also

Whats the serial number so we can look
Customer: replied 4 years ago.
il dont have oil cooler. engine serial 0d389139

a leak down test will pinpoint the oil failure

what it does is fill each cylinder with air, the air will leak out the problem area
Customer: replied 4 years ago.
can i exclude maniphold probleme is it posible that water get in the oil because of maniphold
yes but it has to suck it from exhaust

a compression check will see if the head gasket is bad
Customer: replied 4 years ago.

does the engine block can be so rust by salt water that the block leak in my oil pan do you ever see it because engine run good so i will do the test you ask but ???

Customer: replied 4 years ago.
Relist: Answer came too late.

Hi my name isXXXXX will assist you.


These engines will get an internal leak due to salt water corrosion. I know that engine rebuilders will not rebuild a engine that has been exposed to salt water due to the amount of metal lost from salt water corrosion. Since the water is getting in to the oil it is most likely a crack or the block has rusted through due to salt water corrosion. If you are not getting water in to the cylinders this also points to the engine block being cracked or rusted through. Are you getting water in any of the cylinders?

Customer: replied 4 years ago.

i will do pressure test in my cylinders so if i dont find nothing you sugges to replace the engine ? like i ask before you dont expect probleme whit maniphold ?

The manifold if it rusts through it will dump allot of water in the engine. There could be a water leak at the gasket but you said you already tried that. If you had the manifold off you would have seen the leak or the hole in the manifold.
Customer: replied 4 years ago.

so if i have leak at maniphold engine can suck water and this water get in the oil by ring and pistons is that what you said ? SO I shoud try know good manipholds before replace the complete engine because if probleme is with manipholds i will still be in trouble even if i change complete engine

In your opening statement under already tried you said you had done all of those as in already tried. I ask do you have water in the cylinders and got no answer. If you read what I wrote you would already know what you need to do. Since you don't understand I will opt out for another expert to explain. It isn't worth my time to get a bad rating so I am done. Here is what you wrote. " Already Tried:
elbows maniphold and intake gasket i dont think it is a freezing crack probleme because i drove the boat 2 months this summer and all was working good .half of pinte of water get in the oil pan afterXXXXXand oil start to come off the engine by the deep stisk" So lets start over what have you done? What have you checked? I am completely confused as to what you have and haven't done.
Customer: replied 4 years ago.

first i am french canadian so i speak english maybe as good as you speak french it may be why it hard to comuniquate . yes i replace elbows maniphold and gasket and i even reface in machine shop the maniphold but i did not do pressure test on maniphold i was only wondering if water can get to engine by manipold by the way it is not the first time i use the service and i never give bab rating to a thecnicien

OK I understand now I will try to be clear as I can. Your English is allot better than my French as I don't speak any French. My apologies.


Their are 3 manifolds on the engine 2 exhaust manifolds and one intake manifold. If the exhaust manifolds get holes in them you will get water in the cylinders. Thats why I ask if you have water in the cylinders? Now if the intake manifold leaks it will leak into the oil not the cylinders. Now if you have no water in the cylinders you have a bad intake or cracked block. If you have water in the cylinders you have bad manifolds or a bad cylinder head or blown head gasket. If you do a pressure test on the cylinders and they check good that leaves the exhaust manifolds, intake manifold or a cracked block. There is no pressure test you can perform on the intake or the exhaust manifolds only a visual inspection. If you have to replace the engine I would replace the exhaust manifolds and risers anyway on a new engine. So check for water in the cylinders. If no water in the cylinders you have a bad intake or a cracked engine block. This is the easiest to do just remove the spark plugs check for water.

Customer: replied 4 years ago.
ok thank you

Your welcome...........Post back with questions if you run into an issue along the way.

Thank you in advance.......Tan

Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10806
Experience: 40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
Tan and other Boat Specialists are ready to help you
Customer: replied 4 years ago.

ok i took the boat off water and i change oil and fiter then i put air in cylinder and there no leak , plus compressure test is ok then i start engine on my drive way i let it run at differente speed betwene idle and 4500 rpm for one houre

and no water get in to the engine so i desceded to put baot in water again i drove it fo 10 minutes and water still get in oil i dont understand can it be about maniphold traps ?

It can be manifolds, engine block or intake manifold. All you eliminated was the cylinders. If you have a crack in the engine block near an oil passage water will get in the oil. If there is a crack in the intake manifold in the water passage it will get in the oil. There are no pressure tests that can be done on the manifold. Now you can pressure test the cooling system of the engine block. If you pressurize the cooling system leaving the exhaust manifolds out of the loop that will narrow it down to the block and intake. But there again you may not be able to see the leak. The intake you can do a visual inspection with the intake removed. If no cracks are found in the intake manifold that leaves the engine block.
Customer: replied 4 years ago.
i anderstand what you are trying to explaine to me and i apreciate your patient but why oil stay clean with boat on trailer and get contaminated with water as soon as i drive on water dont forget the engine stay straig on trailer and on water the engine move from srait to up and down dot you think it may have a effect
On the trailer there is no strain or load on the engine but when you put it in the water and put a load on the engine the stress could open a crack in the block. Besides there is only 1 way the water can get in the oil is through a water passage. The water and oil passages run next to each other in the block.
Customer: replied 4 years ago.
so let take that motor out i wish i be ok only whit only a new engine i will try my old maniphold first with that new engine and if water still get in oil i will buy new maniphold so thank again i was expecting a miracal solution but money and labor will set the probleme thanks again Andre from quebec canada
Why would you use old manifolds on a new motor just to find out if they work? Water in a new engine is not a good idea. Why not just pump the oil from the old engine and put new manifolds on the old engine. Then if you get no water in the oil of the old engine you saved allot of money. If you still get water in the oil of the old engine with new manifolds it is allot cheaper than contaminating the new motor with water. Anytime you get water in the oil in the engine it cuts the life of the engine. You have contaminated all the internally lubricated components with water which rusts immediately on clean metal.
Customer: replied 4 years ago.
thank you for your advice you told me before new maniphold shoud be installed whit new engine so maybe i shoud start with new maniphold on my old block and then go to a new block if it still not working . thank and wish you good end of summer i hope you may do more boat ride then me because it dont look good for me for this summer bey Andre
Correct I always put new manifolds on a new engine. Cheap insurance, risers are good for about 350-400 hours in salt water. Manifolds 500-600 hours.
Customer: replied 4 years ago.
i want to rate you as a good answer but there a advice whow tell me i will be charge if i rate you more then good do you know how is going to cost me because i did pay alrayday if i have to pay againe for the questions you answer me tonight i will pay i only ask thank again Andre
No you don't have to pay me again or rate me again. You are good to go Andre good luck. If you rate me again they will charge you just don't rate as you have already done that. Thank you.Tan

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