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WakeWorld Discussion Board » >> Boats, Accessories & Tow Vehicles Archive » Archive through January 14, 2005 » 350 mercruiser that burns OIL « Previous Next »
By scott smith (sherman) on Friday, October 01, 2004 - 7:34 pm:    Edit Post Delete Post
My 2003 350 burns 1qt of oil every 16 hours. For some reason this dosen't sound right. If you have the same prolbem let me know. Why would a motor company that dose so much testing in racing motors put out a product that burns so much oil. The company told my dealer that is normal. What do you think?
By Jason Pribyl (skibum69) on Friday, October 01, 2004 - 8:56 pm:    Edit Post Delete Post
I would say that is not normal, I don't have a mercruiser, but my indimar never burns oil, even during break-in. I would contact mercruiser's customer service department directory, sorry I don't have any number for you though
By Peter Chandler (peter_c) on Friday, October 01, 2004 - 9:27 pm:    Edit Post Delete Post
How many hours do you have on it?
By scott smith (sherman) on Friday, October 01, 2004 - 10:09 pm:    Edit Post Delete Post
I have about 425 hours on the motor
By Darren Yearsley (ralph) on Friday, October 01, 2004 - 10:12 pm:    Edit Post Delete Post
Has it always burn oil or has it just started? My 350 mag burns zero @ 155hrs.
By Sean M (magic) on Friday, October 01, 2004 - 10:22 pm:    Edit Post Delete Post
My 2001 350 has about 270 miles on it and have never burned a drop.
By trace (trace) on Friday, October 01, 2004 - 10:22 pm:    Edit Post Delete Post
not normal. i had a Camaro with 250,000 miles on it that only burned about 1/2 quart every 5k miles when i sold it. assuming there are no leaks, do you know if it was broken in properly? does it smoke?
By scott smith (sherman) on Friday, October 01, 2004 - 10:59 pm:    Edit Post Delete Post
by the way its a mercruiser tow motor
By Peter Chandler (peter_c) on Friday, October 01, 2004 - 11:23 pm:    Edit Post Delete Post
Do you see smoke when you first start it hot and/or cold?
By Peter Chandler (peter_c) on Friday, October 01, 2004 - 11:24 pm:    Edit Post Delete Post
Run a compression test on it hot and let us know what the readings are.
By trace (trace) on Friday, October 01, 2004 - 11:26 pm:    Edit Post Delete Post
are you asking me? the boat has an Indmar, and Camaro had a 305, but they're all GM smallblocks including your Merc. everything that has to do with the crank case oil is virtually identical. no engine should burn that much oil unless something's wrong with it.
By scott smith (sherman) on Saturday, October 02, 2004 - 8:45 am:    Edit Post Delete Post
When I start the motor cold or hot their is no smoke. Mercruiser told my dealer that with all the starting when the motor is warm than the motor cools that oil leaks by the rings and gose out the exaust. It dosen't sound right to me The motor was broke in the right way Well that must say something about mercruiser they say that is normal. Sounds like they need a better R&D dept.
By Mark Anderson (puckinshat) on Saturday, October 02, 2004 - 9:07 am:    Edit Post Delete Post
I think I have the same engine, but mine burns a VERY minmal amount of oil. It smokes after being ran for a while and then sitting for a while. Just like in between sets and stuff. The engine does has over 1200 hours though.
By Rick H (blastmaster) on Sunday, October 03, 2004 - 6:50 pm:    Edit Post Delete Post
You need to ck the PCV valve. If it is bad it will allow the engine on acceleration to suck raw oil out of the valve cover and burn it. Your plugs will look brown and gunked up. That is a really cheap fix and they go bad really easy. If this is the case you might not see white smoke because it is a very small amount of oil.
If this is the case any brand engine would burn the same amount of oil. Just a thought.


By Rod McInnis (rodmcinnis) on Monday, October 04, 2004 - 10:47 am:    Edit Post Delete Post

There are three common reasons for a motor to lose oil. Buring it is only one possibility, the others are leaks and blow by.

The common source of burning oil is worn valve guides. The valve guides need to be oiled a tiny amount will always leak down the valve stem and sucked into the engine during the intake cycle. As the valve guides wear and the fit between the guide and the valve stem gets a bit loose it can allow excessive amounts to leak in. The oil leaks into the cylinder and gets burned. If the amount is excessive you should be able to see the result on the spark plugs. Sever cases will even foul the plugs.

Worn piston rings can cause gases to pass between the cylinder and the crankcase. In your tow vehicle, going down a steep hill and using the engine to slow you down you can get quite a vacuume in the cylinder and actually draw oil mist from the crankcase into the cylinder and burn it. That situation is hard to achieve in a boat, however. What can happen is under heavy acceleration and especially at high RPMs the high pressure inside the cylinder leaks into the crankcase. This creates a high flow of air through the crankcase, which picks up oil mist and carries it along for the ride. This goes out the breather and is either lost out the vents or sucked back in the air intake, which I suppose could be considered burning it.

A third source of oil loss is leaks, which should be obvious by the mess it creates in the bottom of the boat.

A valve guide problem is hard to prevent, it isn't an issue of break in. Extended high RPM runs might cause problems. 425 hours seems a bit early for this problem, but not that rare.

Piston rings would be my first guess. Improper break in can lead to an early problem. Engines that sit idle for months (like a boat sitting all winter) are really prone to ring problems because the cylinders rust during the periods of non use, the walls get pitted and then the pits wear at the rings.

Ring problems will be much worse at high RPMs. The engine may do fine at 3500 RPM but if you run at 5000 RPM the oil loss might be considerable.

Question: Do you smell buring oil at any time?


By scott smith (sherman) on Monday, October 04, 2004 - 5:22 pm:    Edit Post Delete Post
I dont smell oil burning at all. just the loss of oil after 16 hours


By Duane Wheeler (wakebordr11) on Monday, October 04, 2004 - 6:01 pm:    Edit Post Delete Post
no it isnt normal, my engine has 450 on it and it doesnt burn oil at all to my knowledge, OCCASSIONALLY after a day of long riding after the engine cools all the way and sits for 3 hours or so while I eat dinner it will start rough and smoke a tiny amnt but I dont know if it is oil or not, just a rough start. Get it checked out, its not anywheres near normal
By Duane (nvsairwarrior) on Tuesday, October 05, 2004 - 6:53 am:    Edit Post Delete Post
I agree it is NOT NORMAL! My 2000 Merc 350 MPI now has 950 hrs and does not burn/leak/blow any detectable amount of oil between changes.
That level of consumption/leakage etc, will leave some evidence as to what is happening. Good tips above. Careful visual inspection of the engine exterior for leaks, then wipe the bottom of the pan with your hand or clean cloth. Some leaks will drip off the bottom of the pan and not be visible otherwise. One of the last things to check might be a compression check. But like others, I don't think you have a wear issue.
Check each tip above and let us know which one it is.
Good luck

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