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What's the difference between 5w40 and 15w40?

52K views 46 replies 17 participants last post by  TDavis1992 
#1 ·
Hey guys and girls, just wondering what the difference is between 5w40 and 15w40? I have a 2002 chevy with 170000km on it and about to put amsoil in just not sure what to get cause I don't know the difference. Can anyone please help out.

Thanks all

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#2 ·
15w40


2004 Silverado LT LB7

Moded air box with custom 5 inch Steel tubing, Full EGR delete with fed up pipes, IAH Delete, fed y bridge, PPE Turbo Horn, shortened drive belt, LBZ CP3 running LB7 FPR, port/polish on IHI with rebuild, Batmo Wheel, PPE boost valve, 3.5 inch down pipe, Full turbo back 5 inch exhaust, Airdog 2 165, red head power steering gearbox, Tie Rod Sleeves, Cognito control Arms, Cognito pitman and idler arms, EFI Cory Willis Tunes, all aluminum transfer case, 33x12.5 nitro a/t on 20 inch Rhino lined American Racing Rims, 4 pair high discharge LED lights behind grill and under trailer Hitch, Rhino Lined bull bar, Bushwacker pocket style riveted fender flares painted to match, Triple Glowshift Gauge A-pillar with Boost/EGR/Low side fuel pressure @ lifter pump, LG Tablet by Verizon on flex pedestal running Torque Pro for real time logging/detailed measurement in realtime/gps speed logging, low and hi beam 4300k HID, pump rub kit, aluminum transfer case, @ 325k miles
 
#3 ·
5w40 is to get thin, it will expose all your leaks and pour out everywhere


2004 Silverado LT LB7

Moded air box with custom 5 inch Steel tubing, Full EGR delete with fed up pipes, IAH Delete, fed y bridge, PPE Turbo Horn, shortened drive belt, LBZ CP3 running LB7 FPR, port/polish on IHI with rebuild, Batmo Wheel, PPE boost valve, 3.5 inch down pipe, Full turbo back 5 inch exhaust, Airdog 2 165, red head power steering gearbox, Tie Rod Sleeves, Cognito control Arms, Cognito pitman and idler arms, EFI Cory Willis Tunes, all aluminum transfer case, 33x12.5 nitro a/t on 20 inch Rhino lined American Racing Rims, 4 pair high discharge LED lights behind grill and under trailer Hitch, Rhino Lined bull bar, Bushwacker pocket style riveted fender flares painted to match, Triple Glowshift Gauge A-pillar with Boost/EGR/Low side fuel pressure @ lifter pump, LG Tablet by Verizon on flex pedestal running Torque Pro for real time logging/detailed measurement in realtime/gps speed logging, low and hi beam 4300k HID, pump rub kit, aluminum transfer case, @ 325k miles
 
#15 · (Edited)
5w40 is to get thin, it will expose all your leaks and pour out everywhere
That is not a true statement. There is a whole back story to exposing leaks with synthetics and ob_1jr touched on it.

The 5W or 15W numbers are what the oil is cold on start-up. They are both a 40 weight oil at operating temperatures. If you live in a very cold area where overnight and or daily temps don't get above -17c or 0f, ie: Alaska, Northern Territories, Yukon Territory, Nunavut in Canada then you may want to look at using a 5W-40 or even a 10W-30 or 5W-30. If you live in an area that the coldest temp on a regular basis is -6c or 21f and above the 15W-40 would be fine. here is a little tidbit of info for you, the 5W-40 cold pour point (where it turns to a consistency of honey) is -46c or -51f, the 15W-40 is -40c and -40f, the 5W-30 is -50c or -58f.

I am an Amsoil Dist and know the product line very well. If you would like anymore info or like to buy at wholesale pricing I would be happy to help shoot me a pm or call and we will give you all the time you need to ask questions.
 
#6 ·
Because tolerances in our lb7 motors are not as sever as that of the lly, lbz, and lml. That number referee to how thin the oil is cold


2004 Silverado LT LB7

Moded air box with custom 5 inch Steel tubing, Full EGR delete with fed up pipes, IAH Delete, fed y bridge, PPE Turbo Horn, shortened drive belt, LBZ CP3 running LB7 FPR, port/polish on IHI with rebuild, Batmo Wheel, PPE boost valve, 3.5 inch down pipe, Full turbo back 5 inch exhaust, Airdog 2 165, red head power steering gearbox, Tie Rod Sleeves, Cognito control Arms, Cognito pitman and idler arms, EFI Cory Willis Tunes, all aluminum transfer case, 33x12.5 nitro a/t on 20 inch Rhino lined American Racing Rims, 4 pair high discharge LED lights behind grill and under trailer Hitch, Rhino Lined bull bar, Bushwacker pocket style riveted fender flares painted to match, Triple Glowshift Gauge A-pillar with Boost/EGR/Low side fuel pressure @ lifter pump, LG Tablet by Verizon on flex pedestal running Torque Pro for real time logging/detailed measurement in realtime/gps speed logging, low and hi beam 4300k HID, pump rub kit, aluminum transfer case, @ 325k miles
 
#8 ·
Most use the 5W40 in colder climates, there are some threads about it on here.
 
#9 ·
Because there's certainly no information regarding oil viscosity and brand choice on the world wide web.

Ready for my opinion?
In the manual that comes with the truck, there is one difference between 15w and 5w when it comes to recommendations. 15w 40 isn't the best when temperatures dive below 20 degrees Fahrenheit, yet 5w 40 is recommended for ALL climate types within reason... So tbh I think is idiotic to use something obviously less capable since at operating temps they are turned into basically the same oil.

What that guy is talking about oil leaks is ridiculous, a properly maintained motor shouldn't even leak water if you were so inclined to pour that in.
 
#20 ·
Because there's certainly no information regarding oil viscosity and brand choice on the world wide web.



What that guy is talking about oil leaks is ridiculous, a properly maintained motor shouldn't even leak water if you were so inclined to pour that in.
Glad someone stepped to the plate and stated this. I almost spewed coffee on the screen when I read that. Best to simply not reply if you don't know what the viscosity ratings are with oil.

I live in Florida, so I use 15W-30 year round. When cool (or cold for those in northern winter climates), the oil viscosity is 15W. When warmed up, it becomes 40W.

It's just that simple. And if 5W oil was leaking from your engine, you'd have some serious issues with seals and gaskets!
 
#10 ·
Based on the mileage of his motor that guy is accounting for the wear and tear on the motor. You are correct with the climate and such so if you are in Canada or northern us, I would go with lesser viscous oil. But how about you send him to any oil change place or dealer and get their opinion. Dollars to dimes I bet they tell you what I said.

Also, if it was an lb7 with 70k on the clock I would use 5w in it but since it has 170k I am going to play it safe and say 15w.

Oil weight refers to two connotations when viewing the rating. Just run over to Mobile or pens oil web site and look at how to read an oil rating. Because that's what it is, a rating to determine the appropriate time to use it.


2004 Silverado LT LB7

Moded air box with custom 5 inch Steel tubing, Full EGR delete with fed up pipes, IAH Delete, fed y bridge, PPE Turbo Horn, shortened drive belt, LBZ CP3 running LB7 FPR, port/polish on IHI with rebuild, Batmo Wheel, PPE boost valve, 3.5 inch down pipe, Full turbo back 5 inch exhaust, Airdog 2 165, red head power steering gearbox, Tie Rod Sleeves, Cognito control Arms, Cognito pitman and idler arms, EFI Cory Willis Tunes, all aluminum transfer case, 33x12.5 nitro a/t on 20 inch Rhino lined American Racing Rims, 4 pair high discharge LED lights behind grill and under trailer Hitch, Rhino Lined bull bar, Bushwacker pocket style riveted fender flares painted to match, Triple Glowshift Gauge A-pillar with Boost/EGR/Low side fuel pressure @ lifter pump, LG Tablet by Verizon on flex pedestal running Torque Pro for real time logging/detailed measurement in realtime/gps speed logging, low and hi beam 4300k HID, pump rub kit, aluminum transfer case, @ 325k miles
 
#12 ·
5w40 will flow better at colder weather. although, with that many miles, I would go a different route as far as oil. the amsoil will clean out all the deposits and expose your leaks. it will do the same with 15w40. My LB7 didn't like the amsoil very much (not sure if it was just because one winter my truck sat outside in alaska or not) I had a small amount of oil coming out the blow-by tube on the front passenger's side of the engine. I started using rotella-T and I didn't see as much coming out, but still had some.

If you routinely see below 0 and can't plug in your truck (providing you have an oil pan heater), go with the 5w40. It doesn't really matter the brand. Each and everyone had different experiences. For every person that has a negative experience, you will find 10 that have positive. You only really hear about the negative anyway. For me I couldn't tell you if it was the amsoil or not for sure since I still had some oil coming out the blow-by tube no matter what oil I used. Funny thing was I rarely had to add oil...maybe 1 qt in 5K miles no matter which oil I used, which isn't bad.
 
#14 ·
I worked in an oil analysis lab and never saw any engine damage related to running a lower cold viscosity. What those numbers mean is that the oil acts like a 5 weight oil (or 15) when it's cold and 40 weight at engine temperature. I'd be interested in knowing whether anyone else has. The only thing we noticed is that the wider the range of the viscosity improver the quicker the improver broke down. When I was looking at putting synthetics in my truck (which I did) I did some digging and one engineer told us that the main reason a 15W40 was recommended vs. 5W40 was to meet the extended oil change intervals called for by the EPA. Knowing what I knew from the oil lab that made sense. I use the Rotella full synthetic available at Walmart and it comes in 5W40 and have my oil analyzed and there's never a wear issue.

If your oil has been changed regularly you shouldn't need to worry about changing over but if you just bought a truck and think it has buildup, a lot of people swear by the old school method of draining off a quart of oil and dumping a quart of ATF in the crankcase. It will keep the crud in the engine in suspension in the oil so that it drains out with the oil but won't break loose chunks and plug stuff up like some engine flushes do. You leave it in for a couple hundred miles of regular driving (not towing or anything) and then do your oil change.
 
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#16 ·
Then I stand corrected, I was told by my dealer that would expose leaks. Such is the principle reason I have kept 15w40 tradition and never switch to synthetic or used lighter oils. But to be fair I live in Texas, an area of higher temperatures


2004 Silverado LT LB7

Moded air box with custom 5 inch Steel tubing, Full EGR delete with fed up pipes, IAH Delete, fed y bridge, PPE Turbo Horn, shortened drive belt, LBZ CP3 running LB7 FPR, port/polish on IHI with rebuild, Batmo Wheel, PPE boost valve, 3.5 inch down pipe, Full turbo back 5 inch exhaust, Airdog 2 165, red head power steering gearbox, Tie Rod Sleeves, Cognito control Arms, Cognito pitman and idler arms, EFI Cory Willis Tunes, all aluminum transfer case, 33x12.5 nitro a/t on 20 inch Rhino lined American Racing Rims, 4 pair high discharge LED lights behind grill and under trailer Hitch, Rhino Lined bull bar, Bushwacker pocket style riveted fender flares painted to match, Triple Glowshift Gauge A-pillar with Boost/EGR/Low side fuel pressure @ lifter pump, LG Tablet by Verizon on flex pedestal running Torque Pro for real time logging/detailed measurement in realtime/gps speed logging, low and hi beam 4300k HID, pump rub kit, aluminum transfer case, @ 325k miles
 
#17 ·
Then I stand corrected, I was told by my dealer that would expose leaks. Such is the principle reason I have kept 15w40 tradition and never switch to synthetic or used lighter oils. But to be fair I live in Texas, an area of higher temperatures
The only reason you would have a leak is if you had a bad seal. That is not very common these days because the seal material has come along way and been improved over the old days back in the 70' 80' and up to mid 90's. Changing from one oil to another or from conventional to Synthetic will not cause a leak by itself. It will, as ob_1jr explained, expose a bad seal if you have one. Why? Because synthetics have a higher detergent content which means they clean your engine better as you drive. This is why there are stories of motors with hundreds of thousands of miles on them and when pulled apart they look new. If you have a seal being prevented from leaking by what is termed "sludge" in the industry (which is really vaporized oil from heat) the synthetic could clean that sludge therefore causing or exposing that leak. If you dont have any bad seals then you won't have a leak by going to a 5W-40 or switching to synthetic from mineral oil.
 
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#18 ·
to ad to this:
The letter following the first number "w" has come to be called "weight" but it is not actually, it stands for "winter". This is the lowest temp that it will flow at. 5w40 Is at 5 degrees it will flow and anything colder will make it flow less. Likewise 15w40 is at 15 degrees is the lowest it will flow at.

The "weight" of the oil is found on the label and is usually listed in Once, Quarts, or Gallons (liters outside the USA).

The second number is the Viscosity this is what you consider for your driving engine temp. This will vary depending on your engine, unless you have a built LB7 with tight tolerances the 40 is all you will need.

Just wanted to point this out as it helps to understand your oil and running the right oil for your region.

For most trucks a 5w40 is a safe oil

I run a 0w40 for where I live due to temps hitting -20 and lower in January. It only matters really if the truck sits somewhere to cool off enough to get to ambient temp. If you have a block heater or park in a heated garage not that big of a deal.
 
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#19 · (Edited)
to ad to this:
The letter following the first number "w" has come to be called "weight" but it is not actually, it stands for "winter". This is the lowest temp that it will flow at. 5w40 Is at 5 degrees it will flow and anything colder will make it flow less. Likewise 15w40 is at 15 degrees is the lowest it will flow at.

The "weight" of the oil is found on the label and is usually listed in Once, Quarts, or Gallons (liters outside the USA).

The second number is the Viscosity this is what you consider for your driving engine temp. This will vary depending on your engine, unless you have a built LB7 with tight tolerances the 40 is all you will need.

Just wanted to point this out as it helps to understand your oil and running the right oil for your region.

For most trucks a 5w40 is a safe oil

I run a 0w40 for where I live due to temps hitting -20 and lower in January. It only matters really if the truck sits somewhere to cool off enough to get to ambient temp. If you have a block heater or park in a heated garage not that big of a deal.
Deathpiggy I am not trying to start a fight or attack you by any means. I am merely trying to disseminate correct info for those that are new to this and are trying to learn and do research on this subject.
The part I have highlighted is incorrect. If anybody wants to know the lowest point it will flow or pour you want to look into the specs/data sheet and see the cold pour point. For instance if you look at this data bulletin for the 5W-40 Amsoil, scroll down and look at the cold pour point its -51f. Anything above that the oil is flowing, at that pour point temp or lower the oil turns to a honey like consistency. Compare that to Delo 400 conventional oil at -31f Delo 400 SD product data sheet which would you rather have when the weather is colder than a well diggers a$$.
 
#21 ·
And to state that the "W" has to do with winter, that's bending a bit. A lower viscosity or "weight" is used in colder climates sot the oil can flow, as stated by dirtbikindad, and as the engine warms, it gets thicker, and in this case, becomes 40 weight.

The numbers have nothing to do with outside temps, meaning 5 weight flows at 5 degrees. If that were the case, I'd have to run 90W gear oil in my engine during the Florida summers when its 98+ degrees outside.
 
#23 ·
If that were the case, I'd have to run 90W gear oil in my engine during the Florida summers when its 98+ degrees outside.
You'd probably have no issue running a 40 straight weight tbh.

There's just so much wrong in this thread.
5w-40 has a broader operating range than 15w-40. Unless you're penny pinching or you're misinformed about synthetic oils, it's stupid to pick the 15w-40 option.

There is a single benefit to 15w-40 oils though, they will maintain their 40 weight operating viscosity longer than an oil that starts at 5w. This is not rocket science, it takes less friction modifiers to get from 15 to 40 than it does from 5. This ONLY comes into effect when oil is used past the 10k mile point or is being used in severe duty.

You guys are over thinking this WAY too much.
 
#22 · (Edited)
#26 · (Edited)
Ams offers Syn in both 5w and 15w, IIRC.
 
#30 ·
Yes I underatand that. But having a 5w in the summer will only be that must easier on it to start, and not change start up? I'm not trying to be rude or anything. When I first got the truck I got fucked around on injectors for $10k I want to be 100% on everything from here on in. I appreciate everyone's input and explaining everything about oil.

Sent from my SM-G900W8 using Tapatalk
 
#31 ·
I run Schaeffer's 9000 full syn 5w40....in Texas triple digit heat.
You'll be a'right. :farmer
 
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#33 · (Edited)
wow there are some interesting opinions in this thread.



5-40 does not make your truck leak, if your truck leaks after you put 5-40 in then your engine was already worn out.

5-40 is thinner in the cold. there is no need to run 5-40, however those who live in cold climates that frequently get below 0 may experience easier starting, less wear and tear on the engine, and quicker warm up times with 5-40.
 
#34 ·
Oil threads such as this always lead to misinformation, hence the reason for all the posts.

When ever in doubt, follow the advice of your owners manual. It will state the recommended viscosity range to use based on your climate area.
 
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