View Full Version : 30 or 40 weight oil?

Vibe Ray
08-09-2001, 02:37 AM
Hey guys, I was wondering when should you use straight weight 30 and straight weight 40 oil? I am using straight weight 40 oil right now, but am curious as to whether or not I should use SAE 30 oil. Thanx!

08-09-2001, 04:48 AM
30 wt is recomended for air cooled engines, Where do you readily
find 40 wt? Some engines with hydraulic lifters require a multi
viscosity oil, but Never use 10w40 in anything!

Vibe Ray
08-10-2001, 02:37 AM
I am getting Pennzoil SAE 40 pretty much from anywhere I go around here. (K-Mart, Wal-Mart, Auto stores, you name it). What happened is I read the Kawasaki manual and looked at the chart to determine what type of oil I should use and it looked like Sae 40 would work best for my application cuz we get pretty hot down here. But I never here anybody using straight weight 40 and I was wondering why not. Am I using the wrong oil? Anyone able to let me in on the truth?

wesley daniel
08-14-2001, 11:16 AM
The part 5w,10w,15w ect. is the viscosity of the oil. 30w 40w 50w is the weight. A 5w 40 has the viscosity of a 5 weight oil but
the protection of a 40 weight oil and so forth.Up north where it is colder you need a lower weight oil.If you ever noticed the lower the weight the easier it poures. When you run the motor a while it heast the oil up and it will pour real fast.
When you first start a motor a straight 40w will be thick and wont flow to the bearings right away because it is thick, and the motor is cold if the ambiant temp. is below 75 . But a 10w40 will flow because it has the viscosity of a 10w oil,and will protect the bearings at colder temps.
Your climate is about the same as houston . I run a 10w30
in the winter and when the temp sticks around 70 I run 30w When it gets and stays above 90 I run 40.

Hope this helps.

08-14-2001, 02:42 PM
But NEVER use 10w40 in an air cooled engine!

plow kid
08-15-2001, 01:22 AM
I run 40w in everything now, I get it at Tractor Supply Co [ TSC ]
it comes in 5 gallon buckets for $21.95, I see a increase in oil pressure with strait 40w over 10w-40

08-15-2001, 10:39 AM
We use four different types of oil for all our equipment: 30wt, mainly in all engines; 10w40, some hydraulic systems and a few engines; ISO 068(Turbine Oil), hydraulic systems(mainly Toro); and Hydraulic/Tractor Fluid, hydraulic and tractor transaxles.
30wt Heavy Duty motor oil is a good all around engine oil that works well in all US areas. Multi-weight oils can be used, but are mainly for areas where wide temperanges exisit, below freezing to extremely hot. Not to slam Wesley, but he is not quite right about what multi-weight oils are. For 10w30, when the oil is cool/cold its viscosity is 10 weight(thinner, flows easier) and when it is at normal engine operating temp its viscosity is 40 weight(thicker, better protection for bearings since it will not be splashed away as easy). In extreme cold weather it is important to have an oil the flows easier and not be to thick to flow like honey.
Synethics work pretty much the same way, except the do not break down under extreme heat conditions like standard petroelum based oils do. Note many new hydro systems that require synethic oil, means they generate or retain more heat than the other hydro systems.
It is also important that you don't mix brands of oil, when added oil. Some brands have additives that don't mix well. I have seen one engine that had what ever the cheapest brand of oil added(oil changes not to often) that siezed. After splitting the case, all the oil had solitified in the bottom and was the consistancy of butter. Not a pretty sight! This is very rare, but can happen.
The main thing to remember is to use oil that is equivalent or better than what the manufacture recommends.

08-15-2001, 11:54 AM
When 10w40 breaks down it is very nasty, usually ruins the
crank and whatever bearing it seizes first. 30 wt does not break
down, which is why I recommend it over multiweight oils, except
in very cold weather or where hydraulic lifters need it, but never
10w40, it is the most prone to multi-viscosity breakdown.

Vibe Ray
08-16-2001, 03:10 AM
Does any brand make a fully synthetic SAE 30? I see 10w- 30, but not SAE 30 in synthetic. I wanna change over to synthetic next oil change (@100 hrs). What about a fully synthetic SAE 40?
BTW, thanx for the help guys.

Eric ELM
08-16-2001, 09:43 AM
I see Fish doesn't like 10/40 oil.

What is your opinion on Rotella T 15/40 oil? I have used it in my diesel Chopper for the past 600 hours and also in my old Kohler that has almost 3,600 hours on it, for the past 700 hours. It sounds like a new engine. I ran it in the Hot summer, the Cold Fall and Spring also. I do let it warm up before cranking the rpm's up to around 3,750 though.

I ran this same oil in my John Deere 430 last winter for plowing snow also. It cranked up like it had straight 5 W in it.

I would be interested in hearing from everyone that has replied here on this oil.


08-16-2001, 11:41 AM
I'm running Mobil 1 synthetic 0w30 in my 25 horse Kohler. According to SDWally this would be a good oil I suppose. It is thin at startup to give quick lubrication and has the viscosity of the standard 30 weight when warmed up. Additionally it is sythetic so it won't break down if it gets heated when you are really working the engine. Is this right?

08-16-2001, 02:22 PM
I think that the 15w40 is better than the 10w40.

The 10w40 needs more/larger plastic to work.

Fish, Are you the same Fish from the Garden Web Board ?

08-16-2001, 06:30 PM
Yea, they were getting tired of me over there. I still pop in to
piss someone off, but Eric invited me, so I thought I would come
over here and start trouble.
For some reason the compound of 10w40 is real bad for
breakdown, I have read reports that all realize this. I always
recommend straight 30w unless there is a reason, I even run
it in my van. I have just seen too many engines desroyed by it
or I would not bother posting. Failures caused by this are
usually misdiagnosed, and since many engine manufacturers
used to recommend this oil, they will not be too forthcoming
to condemn this oil. But type motor oil, oil, or whatever into
a search engine and you can read reports on oil. You will find a
small reference to multi-viscosity breakdown particularly with

John DiMartino
08-16-2001, 07:44 PM
SAE 30 is the one to use,down to 32 degrees in air cooled motors.Below that,go to a 10w30,or 15w40 diesel oil.15w40 is good stufff,and pretty much can be used year round down to zero degrees,but I like to go thinner below 20 degrees.

Vibe Ray
08-21-2001, 03:34 AM
Seriously though guys, is there a synthetic straight weight 30 or even 40 out there? All I see is 10W-30 in Mobil 1. And if the SAE 40 is thicker wouldn't that provide better protection? So why go with the SAE 30?

08-21-2001, 06:46 PM
Mobil makes more than the X/30W in Mobil 1. A friend uses a 15/40 or probably 20/50 in a hot 454 in a speed boat. Might even make a series 3 for diesel.

The Rotella oil is a very high quality oil.

Years ago I switched to oil and grease from TRC - Texas Refinery Corporation. Everything lasted longer. Especially bearings and bushings with the #2 chassis grease.

I now buy equivalent product thru King Oil, Hagerstown Maryland. Both product lines are expensive but worth it.

Another friend sells Husquavarna racing bikes. On regular oil they require rebuild after every race and the bearings show wear. On Mobil 1 they go 2 races and they look like new upon tear down. They still rebuild after 2 races because they don't know how far they can really go.

08-21-2001, 11:18 PM
All air cooled engines will run better, last longer and produce more power with synthetic oil. B&S (and ALL others) highly recommend the use of either 5W-30 or 10W-30 synthetic oil for all temperature ranges. NO OTHER OIL IS AS GOOD! Also, don't worry about "break-in" with dino oil. You can put synthetic in on the first start of the engine. The engine parts will mate just as well with synthetic as dino (probably better). There is only one thing about dino oil that is better...it's cheaper!

08-21-2001, 11:39 PM
Originally posted by Vibe Ray
Does any brand make a fully synthetic SAE 30? I see 10w- 30, but not SAE 30 in synthetic.

Yes, Amsoil makes a SAE 30. I ran it in my gas Kubota for over 2000 hours. I switched to 10w-30 Mobil 1 because I could only get deals buying 4 gallons at a time. At that point we weren't using it that much.


08-22-2001, 05:46 PM
Hey fish, what compound are you speaking of in 10w40 oil?

Remember the car manufacturers used 10w40 for about 20 years in cars without any problems, then shifting to 10w30, and now 5w30. The manufacturers engineers we should all agree would know the best oil for our engines.

For example: The new Honda tractors actually recommend 10w30 or 10w40 depending on the temperature. Whereas Tecumpseh states specifically DO NOT USE 10w40 oil. So which is it?

The best recommendation anyone can give is to read the manual that comes with your equipment and to follow it explicitly. Do not follow myths, wifestales, or statesments that start, "someone told me once". Otherwise YOU could be responsible for voiding someone warranty.

08-22-2001, 06:51 PM
I know oil is a hot topic among people. I typed in motor oil in
msn search engine and came up with this wives tale right off.
I can find other articles referring to multi-viscosity breakdown
if you wish, but I have seen many engines destroyed by it.
Look at paragraph 7 for the first reference.

Vibe Ray
08-23-2001, 02:53 AM
Hey fish, that site looks very informative! I don't have time to read it tonight, but I will later. As far as finding other articles, I insist that you do, cuz I love to learn new stuff!!! BTW, do you have any other informative articles about ANYTHING else? Thanx!

08-23-2001, 03:45 AM
has lots of articles. I haven't read that many yet, maybe this winter, but it is an interesting site.