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Which is the best oil? 10w30 or 10w40?

d9103365

d9103365

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Looking at the owners manuals for our cars, it seems that they were meant to run on just about anything, because specific oil weights are almost never specified.

I have a 1975 fury 318 with 90k original miles, all factory. I live in the south, a warm climate. My car has an old sticker indicating that it had 10w40 at one time, but im not sure what it has now. For my 318s i always used 10w30 because i felt 40 weight was too heavy. I felt that it caused lifter noises and took too long to get flowing on startup. Even now my car lets out a little puff when its first cranked as if the oil takes time to circulate.

Anyway, whats best for these old 318s? 10w30 or 10w40?
 
I don't use any 10W oil. Either 5w or 15w. Ran 5w-30 in my 79 318 van for over 300,000 miles and my 97 Dakota has 260,000 miles on 5W-30. My 92 CTD has 280,000 on 15w-40.
 
Puff at first start can be valve guide seals letting some oil by. Little harm but for fouled plugs.
As for oil, I choose Valvoline 10W40 for flat tappet engines (after break-in) because it's cheap and has sufficient ZDDP. For hydraulic lifters, I tend to use a 15-W oil. I live in hot, hot Texas.
 
Oil will flow at the lowest number when cold. The upper number should have no affect on a cold start would stick with the factory's recommended 10/40 for your climate. Older engines just were not built to the tolerances for 5 weight oil in a warm climate.
 
I would use the 10W-30. I have always been told the 10W-40 has more chemicals in it to make it heavier then the 30 in warm temps and that the 30 is really the better oil. To be honest you could run either and I really dont think you would ever no the difference but for peace of mind I would run the 10W-30 if I were you. Ron
 
Amsoil signature 10-40. High zinc for the 440. 10 weight flow at start up. 0-30 for the modern Hemi's.
 
Using or not using a 10W type of oil really depends on how cold it gets when you drive your vehicle........in the cold weather states it does make a difference. In the warm weather states I would guess it does not matter as much.
I live in Michigan and I have been using 10W-40 in all my classics for years and have never had a oil related problem. In my newer or daily drivers I use what the manufacture requires...usually a 5w-20 or 30.
 
I live in central North Carolina and use straight SAE 30 weight oil. Never had a problem with it. Did they have 10W... or 5W.. oil back in 1970?
 
I use 20-50 valvoline racing oil with 1300+ ppm of zinc for my 440...

is that too heavy?? could it make it easier for the motor to leak oil??
 
I use Brad Penn 10w-40 in both my cars and never had a problem.
 
If you are driving your car in the heat of the summer in Atlanta, I would use the 10W-40 or maybe even 20W-50. In the winter 10W-30 might be better. I've been using Valvoline VR-1 20W-50 Racing oil for years in my 440, but then I'm not driving the car in the dead of winter.
 
It's all pick your own poison stuff.

For a 318, I'd look at straight 30 weight Valvoline VR-1, but that's just me.

Don't know for facts, but looked over the VR-1 info for these days, since I've used Valvoline racing oil in all Mopars I've had. What they say is...the straight weight racing oils are not under the zddp rules, like the multi-weight oils. But I'll add that the racing oils are said to not have high mileage life. Don't matter to me, since I change oil every 3 thousand miles anyway.

The 'recommended' oil weights these days...long story short.
Five years ago, new Chevy Suburban, 5w-30 oil 'recommended'. Of course, the 5w-30 was already in the motor. Went on a trip in the new truck. Halfway through got a low oil light! Had lost 3 out of 5 quarts of oil. Had all checked out after getting back home, including a consumption test, and was told all was good???
Shoved 10w-40 into it after that, and never used another drop of oil. They can 'recommend' anything they want.
 
The multi-grades are thinner when it's cold allowing better flow and the engine to turn over faster upon start-up. Ask anybody who's started an engine that was left outside without a block heater (their not just for diesels!) when it was below freezing. There is a huge difference between 10W/30 and plain 30W!...in the cold. Warmer temps, not so much.

As for a decision between 30 & 40 weight, do you want the oil to be a bit thicker or thinner? Is the engine used hard or commercially?...maybe the 40W. Otherwise it's not much more than a personal preference.
 
I have a 318 in my Dodge Polara and i use 10w-30 and i have never encountered a problem.
 
just did a whole bunch of classes on oils.the multi weight oils are tested for flow at freezing temps,that is how they get the lower ratting.it is the weight of the flow rate at freezing.single grade,30 or 40,have no low temp measurement.so they could be a solid brick at freezing and still be called a 30 wt oil.
newer vehicles have much tighter tolerences to allow the use of the thinner oils.the 10/whatever oils are good for our older design iron block motors,or even the 15/40 diesel oil for us flat tappet guys.you can run the 5/whatever weight oils in our rides,but it is made for the newer motors.now the 0/whatever is only for the newest motor designs,they are built for it.japan is currently testing motors running 0/16 oil on the street,with future testing all the way down to 0/4 in the near future.wrap your head around that one.
 
67 coronet said:
japan is currently testing motors running 0/16 oil on the street,with future testing all the way down to 0/4 in the near future.wrap your head around that one.
Click to expand...

Sure would speed up an oil change. Gets pretty boring waiting for all that 10w oil to drain out.
 
I run 30 W Valvoline VR1 in my 383 RR. It's a pretty hot street motor and flat tappet engines need some zinc. No problems so far.
 
I was a teenager in the 60's and it seemed 10 W 40 was the most commonly used oil. Everyone thought Quaker State was awful and then argued the virtues of other brands, i.e. Valvoline. I had a machinist uncle who thought Wolf's Head Motor Oil was the Cat's ***. I don't even think that's around any more. 5 W oils have become the recommendation of most new car manufacturers these days which I think is due to the better lubricating qualities they have. They're also supposed to help increase fuel mileage. Frankly, I don't think it makes that much difference as long as it is changed along with the filter at recommended intervals. I use 5,000 miles because it's easy to remember when dealing with 5 vehicles when to do it.
 
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