Synthetic Oil in a Mercruiser I/O???????

[springer9861]

I have a 120 hp Mercruiser I/O and I was wanting to know if it would be OK to use synthetic oil in it?(motor, not lower unit) The sales person at the local marina said not to use regular auto oil in it because a boat motor is operated in more severe conditions that a car engine.<br />Let me know what you think!!!! Thanks, Larry

 

[Jacques321]

Re: Synthetic Oil in a Mercruiser I/O???????

Go right ahead and use it with confidence and in knowing that your engine will be well protected in the long run.<br /><br />I'd go with a 10W30 to be well covered in various temperature fluctuations.<br /><br />I went with Mobil 1 tri-synthetic 10W30.<br /><br />I think the salesperson was wrong in saying that you should never use regular oil, but his recommendation to use synthetic oil to guard against extreme conditions is a good one.

 

[petryshyn]

Re: Synthetic Oil in a Mercruiser I/O???????

springer9861, you should have put the salesman on the spot and asked him what the difference in auto oils is. One of the harshest enviroments for oil is in a turbo-charged automotive engine. The oil has to withstand extreme temperatures while passing through the turbo. Most good grade auto oils are capable of this. My question is why would you want to use synthetic in a boat-motor?

 

[MercilessMike]

Re: Synthetic Oil in a Mercruiser I/O???????

Synthetics are FAR superior oils, less breakdown, able to withstand higher temps without breakdown, I a 4 stroker Mobil 1 or amsoil. I use nothing but synthetics in lower unit of my mercs. They are pricey though.<br />OK FELLAS, BUY 2 MOTORS, RUN NOTHING BUT SYNTHETIC IN 1 MOTOR AND MINERAL BASED IN THE OTHER. AFTER 50,000 MILES TEAR THEM SUCKERS APART LOOK AT THE BORES, measure the bores for wear and out of round,look at the bearings, the rings, the oil galleys,look in the pan, valve seals and stems, AND TELL ME YOU DONT BELIEVE...<br />Why have ALL manufactures now offering syns, Becuase eveveryone whom ran motors and wanted reliablilty and no breakdown do to oil were running amsoil or Mobil 1, Go to any race track and ask around 99.9% will be running syn oil. Why the run motors HARD in a harsh environment. just superior protection no matter how you butter your bread.<br /> <br />less oil changes = cleaner environment.

 

[SS MAYFLOAT]

Re: Synthetic Oil in a Mercruiser I/O???????

One of the main things that has sold me on synthetics is when I had to clean up a oil spill on my garage floor and tools. I noticed then that this stuff is alot more slippery than that of conventional oils. It was alot harder to clean the area up. So I know it has to be good on your engine, no matter what type. I use it in all my equipment, from mowers to my boats. In my work van, I was able to increase my pulling power on the hills. Where I could only top one hill at 45, now my van can top it at 55. Don't be surprised when your idle speed will change when you start to use it. This is a positive proof it reduces friction. Have a great day, there is more fish to catch!

 

[petryshyn]

Re: Synthetic Oil in a Mercruiser I/O???????

This is quite an interesting topic. I'm certainly not an expert, but if I remember right, conventional oil loses its viscosity index after a period of time. eg. 10w30 may have the same pourability as 20w after extended use. This is because oil contains long molecules which get sheared in half as it passes through engine components. If the oil is still used even further, eventually the high ends of the oil get distilled off, carbon accumulates from combustion and the pourability deceases to say a 40w. So one could say that eventually 10w30 will have a similar viscosity to straight 40w.(a dirty 40w). This would obviously cause oil starvation in the first minutes of operation if the engine was started in a cold climate.(major engine wear)So why are engines still around from years ago when we had no syn. oils? The answer is because we change our oils long before this happens. Synthetic oils on the other hand, are comprized of shorter more consistant length molecules and are less likely to get sheared from engine components. Therefore it holds its viscosity index longer. (It stays a multi-grade like 10w30 for a longer period of time) It still accumulates carbon, moisture and acids. Its lube quality is no better than conv. oil. The lube quality is a feature of the additive package mixed into the oil. (eg. small particles of zinc, sulphur) So I guess in a nutshell, if you are going to operate an engine in extreme cold temperatures,(-20F etc.) a syn. multigrade like 0w30 may be a good choice. In boating applications, we don't see this low temperature so that kind of an expensive multi-grade is sort of a waste. In my opinion, you'd be better off using a good conv. oil and changing it more often (flushing out contaminants) than leaving in the synthetic for longer periods of time trying to take advantage of its claim to fame. There is a difference in conventional oil off the shelf. Be sure that it has the recommended viscosity, has the "energy conserving" rating (an additive which reduces friction and improves economy)(unless its going in an application which uses a centrifical clutch). And when in doubt......always go with the manufacturers recommendations. I got to go lay down...alota typin for 1 finger <br />

Good boating!

 

[ODDD1]

Re: Synthetic Oil in a Mercruiser I/O???????

One heckuva post, schematic....enjoyed readin it, glad i didnt have to type it!..LOL..I agree synthetics would be a waste of money an oil in this case... the #1 reason I say stay away is they are TOO THIN...this is an old design engine, no oil temp control of any kind, a recommended straight 30w for 90% of applications...when the boats come in the shop with worried looking customers towing them, saying "I get the motor warmed up and when I idle it I HAVE NO PRESSURE ON THE OIL GUAGE!"....invariably some well meaning individual put a 10w30 in the pan at the last oil change.......

 

[Jacques321]

Re: Synthetic Oil in a Mercruiser I/O???????

ODDD1,<br /><br /> I'm no expert on synthetic oils but how do you figure that the 10w30 was to blame for the no oil pressure problem?<br />And I disagree with you that the thinness of a synthetic would cause a problem to an older marine engine??<br />If anything a synthetic oil would do an older engine some good wouldn't it?

 

[Fouled Plug]

Re: Synthetic Oil in a Mercruiser I/O???????

That is a head-scratcher. I thought the viscosity index meant it performed as a 10W cold, and a 30W at operating temp.

 

[petryshyn]

Re: Synthetic Oil in a Mercruiser I/O???????

If I remember right, 10w30 has the same viscosity as 10w at 32F and the same as 30w at 212F. But. . . . .the ugly thing is, in a harsh inviroment, it loses its multigrade over time and soon may perform as a straight weight.eg. 20w (especially poor quality oils)<br />

Happy Boating!!

 

[ODDD1]

Re: Synthetic Oil in a Mercruiser I/O???????

in a perfect world, you are right, a 10w30, either a syn or mineral oil, would do the job fine.......however, in the real world, where motors dont care what numbers on the can are supposed to mean, this motor needs a heavier oil to perform properly...go get a 25w40 syn, or a straight 30 syn and it will do fine......but syn oils for consumers aren't packaged this way, are they?

 

[petryshyn]

Re: Synthetic Oil in a Mercruiser I/O???????

You're right ODDD1 I'll also atest to this. Some small engine manufacturers recommend straight weight oils eg.30w. I believe it was because in a real harsh inviroment, where splash lube is common, poorer quality multigrades rapidly lose their viscosity rating... (get a load a this!!) An engineer at Our local refinery once told me that simply passing a LOW quality 10w30 through a vane hand pump changed its rating to something close to 10w25.(because of the shearing of the long chained molecules, found in conventional oil) Thats why the darn oil pressure is low in some of these engine. They run on a cheap 10w30 for awhile...soon its a 20w and pressure is down...why is everything so complicated <br />

Happy boating!!

 

[Rex]

Re: Synthetic Oil in a Mercruiser I/O???????

I agree with ODDD1, but check the sending<br />unit when it get hot the presurer will<br />go to ""0"".<br /> good luck Rex

 

[springer9861]

Re: Synthetic Oil in a Mercruiser I/O???????

Thanks for all the Info on the oil's!! I think I'll just put Mercruiser Oil back in it and have peace of mind!!!!! Can somebody tell me what the difference is in Mercruiser oil and the name brand auto oils besides the different packaging it comes in!!! Thanks again.................Larry