Oil Question...

C

CptMorgan

New Member
Mar 10, 2007
22
Northwest Ohio
Boat Info
Seville 18.5' Bow Rider
Engines
Mercruiser 120
ok i posted in the "what type of oil" thread but didnt seem to get an answer yet so ill make a new one....my mercruiser 120 says SAE 30 oil right on the side of the motor...so that brings me to my question can i only use SAE 30 or can i use a different 15w-40, synthetics, etc. as i have heard a lot about on these boards. Thanks!
 
I'd check with a Mercruiser dealer, I can't see any reason why you couldn't use Merc's 25W-40 synthetic blend oil. Has the boat ever been repowered?
 
ok i am definitely a newbie when it comes to the boating scene so can i ask what you mean exactly by "has it been repowered?"
 
Has the engine been rebuilt after undergoing a lifetime of hours service or has it been changed or modified in any way; etc. In other words, is it still stock as came from the factory; or not?
 
Matt,

Just a couple of background questions: 1) Do you have any idea how many hours are on that engine? 2) Does it burn oil?

A 25 year old engine usually has issues with seals and internal components which may lead to a different answer. For example your engine can use a more modern oil but I'm not sure there would be any advantage if it has high hours or burns oil.

-John
 
I have always been under the impression if you have an older motor that has gone years without being ran on synthetics, that it is not a good idea to switch to it. Maybe that just applies to cars...but that is what I have always been told. :huh:

Wesley
 
Wesley,

As you know, oil discussions become "religious" very quickly. I post on a number of automotive forums and boat forums and this issue always cranks up a discussion. For the record, synthetics are great for marine engines...there should be little argument about that.

Would I put them in a gas engine with a 1000 hours on it that has lived its life on dino....no. Why, because more often than not it's very slippery nature sneaks by the seals better than dino. It doesn't happen all the time but enough so that owners with high hour or high mileage engines notice it within a week of switching to a synthetic.

What does that mean? The trade off may be another season or two on the engine but the owner is increasingly unhappy with oil showing up in the bilge and dropping $5-7 per quart to fill it.

Gas marine engines have a limited design life of roughly 2000 hours. How an owner treats them for the first 1000 hours determines if they will ever see 2000. I have seen more than my share that never made a 1000 hours and a few that reach 3000 hours. In each case it comes back to how well the owner maintained the engine especially the oil and fuel systems.

-John
 
playdate-
1) not sure on how many hours are on the motor
2) as i could tell last season it did not burn any oil

first born brought up the reason as to why i had asked the question really....i am a car buff and i have always been told the same thing on synthetics in an old vehicle.... so any help is greatly appreciated.

Thanks!
 
Matt,

In the end it is your choice. If the engine has been behaving well on 30w dino for 24 years and the plugs are clean (are there any deposits on them?), I would probably stick with what has worked so far and save your money for the gas pump and an eventual rebuild/replacement engine (which I would definitely use synthetic in).

You will not hurt anything by going to a synthetic and if you have seal issues you can always switch back and the problem usually goes away.

It's the same story with cars.

-John
 
john-

i pulled a plug yesterday and they are rather "black" i do not know when the last change of them was. should i look for any other problems? it ran pretty decent last season just needs a few carb adjustments i do know that.

thanks!
 
john-

i have attached a couple pics of my plugs. they are a little rusty and def. have carbon deposits on them. suggest to replace?

thanks!
 

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I bought my 1997 330DA, 430 hours on the engines, in December 2006. On the strong recommendation of my mechanic (who is excellent) and his performance engine builder buddy, I made the switch to full synthetic (Mobil 1 15W-50). Both stated clearly that the slippery, leaky folklore is just that - folklore. They did allow that the engine seals and gaskets did have leak problems when synthetics first came out 20 years ago, but that was quickly eliminated as engine parts adapted. They maintain that f the engine didn't leak before, it won't after. So far(20 hours) they have proven correct.

The engine builder (who builds performance racing engines and has a shop where you could do surgery) was clear - less wear and better performance. He said that when they have done tear downs on engines that have run on full synthetic they see clearly less wear. My mechanic said it's ideal for marine engines that run under heavy load for extended periods. He also said he has changed many boats to synthetic over many years and has not yet seen any problems from the switch.

So far, no problems and the engines run like like new (they ran very well before the change - no magic fixes here). I have put the boat through a series of performance runs and compared my results to those published by Boattest.com for the same model, engines and setup. I have matched loads as closely as I can tell. After three runs doing this, including WOT, my numbers match theirs as exactly as I can determine, and maybe even a little bit better, but not enough to consider it outside the range of measurement error.
 
CptMorgan said:
john-

i have attached a couple pics of my plugs. they are a little rusty and def. have carbon deposits on them. suggest to replace?

thanks!
Click to expand...

They looked a lot better than I expected for the age of the motor. It must have been treated pretty well during it's life. I would change the plugs but keep the same type for the season and let's see what they look like at the end of the boating season. It looks like you could go one step hotter but I would rather have you stay with what's been working for this season and adjust next year.

The pictures are a bit fuzzy but what I was looking for (problems such as deposit bridging and fouling) I didn't see. Carbon buildup is expected for a carb engine of that age.

The new plugs will help it start better. Check the wires, distributor cap and coil just to make sure we are getting enough voltage to those plugs.

Also put a little antiseize compound on the plugs threads when you put the new ones in.

-John
 
john-

quick question... on my engine it says use ACDelco R43T spark plug the ones i pulled are R43TS is there a difference and which one should i use? Thanks again!
 
R = Resistor
4 = 14 mm Thread
3 = Heat Range
T = Taper Seat
S = Extended Tip

One is an extended tip plug the other is a standard tip plug. The extended tip plug improves idle stability. "S" plugs can be used in most applications where high engine compression in not used. A high compression engine has different piston to head clearances which limit how far the plug can extend into the combustion chamber.

I would stay with the AC Delco R43TS plugs. Depending how they burn this season you may want to change to R44TS next season.

-John
 
I would stick with the AC Delco plugs this season. They are pretty good plugs. You can always spend more money on plugs but I like to replace them every season just because it gives me better insight to what is going on inside the engine. For owners who don't want to change their plugs every season you can purchase higher end plugs that have better electrode characteristics (platnium center fire).

Don't forget to check the distributor cap, rotor, coil and wires. That is usually the reason the plugs misfire.

-John
 
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