whats the deal with straight 30 weight oil recommended for my engine?

[weider1717]

I did a search but never found what I was looking for. I have a 84 boat with a mercruiser m260..350 chevy with 260hp.

If I remember correctly the manual says to use straight 30 weight oil. I have never changed the oil in it I think my uncle said he THINKS he used 10w40 castrol in it.

why are they agaisnt a mutli viscosity oil in this engine? Should I actually stick with their recommendation or is it BS....

with that said what viscosity would you guys recommend? and should I or should I not stay with straight 30 weight oil.

as far as brands I use I run mobil 1 synthetic in my truck and castrol gtx in my wifes car. I guess I'll stay with those brands or maybe should I try mercruiser 25w40? I find it funny they push their 25w40 but my manual says use straight 30 weight lol.

 

[DJ]

Re: whats the deal with straight 30 weight oil recommended for my engine?

It's NOT BS. They make those recommendations for a good reason.

The duty cycle of a boat engine (harsh) is not comparible to automotive.

The key is the bottom number (25) in the viscosity ratings.

25W-40 MerCruiser oil is good stuff. Otherwise use the 30, as recommended.

 

[Don S]

Re: whats the deal with straight 30 weight oil recommended for my engine?

Fact is, if you don't want to use what is recommended by the manufacturer, do whatever makes you feel good.
Here is Mercs newest recommendation.
The info is also on their website for everyone to see.
http://northamerica.mercurymarine.com/serviceandwarranty/mercruiserfaqs/fueloil.php

 

[weider1717]

Re: whats the deal with straight 30 weight oil recommended for my engine?

ok thanks guys..It looks like and correct me if I'm wrong..although my manual for my 84 m260 engine says to use straight 30 weight oil. They now recommend THEIR 25w40 weight oil OR still the straight 30 weight oil.

basically what I need to do is use their 25w40 weight oil or a good quality automotive straight 30 weight oil and I'll do just that.

you guys are very boat savy in your opinion is one better to use than the other? I'm in south carolina and I wasn't too usre how to read that chart as far as which weight for what temp.

also if I choose to use a straight 30 weight oil does brands like mobil 1, castrol etc..even make a straight 30 weight? I've atlteast never noticed it at wallyworld!

EDIT: I JUST WENT TO CASTROLS WEBSITE..LOOKS LIKE IF I CHOOSE TO GO WITH STRAIGHT 30 WEIGHT OIL I NEED TO PURCHASE THEIR CASTROL HD 30 CORRECT?

 

[Don S]

Re: whats the deal with straight 30 weight oil recommended for my engine?

Every type of oil has been used in a boat and is used by someone and recommended by them. So what's the difference.
Besides, oil threads usually end up in big fights, it's the nature of so many different opinions.

 

[weider1717]

Re: whats the deal with straight 30 weight oil recommended for my engine?

Every type of oil has been used in a boat and is used by someone and recommended by them. So what's the difference.
Besides, oil threads usually end up in big fights, it's the nature of so many different opinions.

True, I understand.

Put it this way then so I have piece of mind..I will be going by manufactuer recommedations by choosing either their mercruiser 25w40 weight oil (synthetic version or regular) OR choosing a quality automotive oil with detergents such as Castrols HD 30 weight monograde oil. Correct?

I looked on my other favorite oils website (mobil1) looks like they don't offer a straight weight so I'll go mercruiser 25w40 or castrol HD 30 I think.

whatcha think there Mr. Don?

 

[Don S]

Re: whats the deal with straight 30 weight oil recommended for my engine?

Works for me.

 

[weider1717]

Re: whats the deal with straight 30 weight oil recommended for my engine?

Works for me.

The only thing I question is they say the list of oils below is in the order of recommendation..lets just say they're not just wanting people to by THEIR oil.

it kinda makes me want to go with the #1 recommendation which is 25w40. Since the straight 30 weight is on the bottom of the list.

desicions decisions.. lol

 

[weider1717]

Re: whats the deal with straight 30 weight oil recommended for my engine?

going with the 25w40.

hey don what is this quicksilver deal? i went to mercruiser.com it shows their oil in grey quicksilver bottles..what happened to the black mercruiser stuff?

is quicksilver mercruiser or what?

does walmart sell this 25w40 mercruiser oil? or quicksilver whichever it is.

do they also carry the mercruiser oil filter for a m260 of am i going to have to go to a boat place for all this.

 

[DJ]

Re: whats the deal with straight 30 weight oil recommended for my engine?

Quicksilver is Mercury.

I would go with the Quicksilver/Mercury oil as opposed to automotive. The marine oils do carry extra corrosion (rust) inhibitors.

The 25W-40 is going to perform similar to a 30 weight when cold and a 40 weight when hot. Remember, marine engines run relatively cold, if raw water cooled. About 170 degrees-tops.

For the few extra bucks, it's worth it, in my book.

The oil filter should be easy to find. Personally, I stick with well known brands like AC Delco or any of the OEM brands. Obviuously MerCruiser/Quicksilver would be first choice.

 

[dan t.]

Re: whats the deal with straight 30 weight oil recommended for my engine?

I run Petrocan 20w50, 800 hours over the last 6 years,who knows how many before I bought the boat, meter says 2300 so far so good (1992 305 chev)

 

[bigbob_FTW]

Re: whats the deal with straight 30 weight oil recommended for my engine?

Every type of oil has been used in a boat and is used by someone and recommended by them. So what's the difference.
Besides, oil threads usually end up in big fights, it's the nature of so many different opinions.

almost as fun as the fight over 2 cycle oil.

 

[edjunior]

Re: whats the deal with straight 30 weight oil recommended for my engine?

almost as fun as the fight over 2 cycle oil.

C'mon now, that wasn't a fight...it was "an opinionated discussion"!

 

[Gary H NC]

Re: whats the deal with straight 30 weight oil recommended for my engine?

Shell Rotella T straight 30 is a great oil also.Any parts stores or truck stops have it in gallon jugs.
I changed my old OMC 4.3 oil twice a year and the Rotella was fine.
Just depends on what price for oil you want to pay..
Rotella was designed for truck engines that go 15k to 20k between oil changes.
Everyone has their favorite.

 

[Don S]

Re: whats the deal with straight 30 weight oil recommended for my engine?

See what I mean, here come all the "I use (Fill in the blank) oil and it works great, and everyone should use it." posts

 

[weider1717]

Re: whats the deal with straight 30 weight oil recommended for my engine?

Shell Rotella T straight 30 is a great oil also.Any parts stores or truck stops have it in gallon jugs.
I changed my old OMC 4.3 oil twice a year and the Rotella was fine.
Just depends on what price for oil you want to pay..
Rotella was designed for truck engines that go 15k to 20k between oil changes.
Everyone has their favorite.

really? wow!

I use shell rotella T with triple protection in my chevy duramax diesel and been changing it every 3k miles...

ofcourse always comes out soot black! haha

 

[lowkee]

Re: whats the deal with straight 30 weight oil recommended for my engine?

Call me crazy, but does't that chart pretty much suggest 40 weight, not 30 weight (unless we're talking Alaska, here) for most fo the season? 50F+ is what I'm guessing most of us boat in. How common is 40W? Does an Advance Auto Parts-esque place sell it?

After all, I don't need my engine to turn over easily when cold, I just bought a new super-huge marine battery. It would be a waste to make it easy!

 

[Chris1956]

Re: whats the deal with straight 30 weight oil recommended for my engine?

Lowkey, SAE-40 oil is very common. It will be a price leader at Advance Auto Parts. I agree that most boaters do not venture out when the temp is 50*F or less, so SAE 40 is the best viscosity for those folks. I always used the Quicksilver 25W-40 since I did venture out when the temps were below freezing, as well as in the high 90s.

 

[JoLin]

Re: whats the deal with straight 30 weight oil recommended for my engine?

Regardless of the oil brand, does anyone know why the recommended viscosity numbers are so high across the board?

These are, after all, automotive engines being run in a pretty cool environment. If it was in my car, and the normal operating temp was 170 or below, I'd be using a 10w-30 or 10w-40 oil to insure that the oil is "thin" enough to lube the internals at cold start. Thick oil is great to keep the pressure up on a worn motor, but generally not so hot for bearings that are in good shape.

It's a matter of curiosity to me, as I might become the owner of a 5.7 V-P in the fairly near future.

 

[bigbob_FTW]

Re: whats the deal with straight 30 weight oil recommended for my engine?

most cars don't operate in the RPM range a boat does. They run high RPM's for an extended period. They need the thicker oil.