Product Reviewed: Signature Series Max-Duty Synthetic CK-4 Diesel Oil 15W-40 (DME)
Current Rating: 4.92 out of 5 stars
Votes & Reviews: 284 vote(s) and 373 user reviews.
Reviewed by BRIANS cummins: 
I use the 5w40 and 15w40 in my 2003 Dodge Ram 2500 5.9 cummins ... when I got the truck it had 378,000 also had little blow-by.. it ran mobile 1 most of its life .. switched to AMSOIL signature series (max-duty) and the blow-by was gone and it also slowed down completely with drinking some oil .. 7-10,000 and I might need to add 1/2 qt this stuff is AWESOME .. now I have 429,000 and this cummins runs like its NEW with 10,000 miles on it .. everyone that I know with a cummins , I get them hocked on it also .. everything I own has AMSOIL
Reviewed by Mark:
I've used Amsoil in my last 5 class 8 trucks. Absolutely no problems. Why on Earth change. Use Sig. 5w-30 in my Ecoboost too
Reviewed by Reg Moody:
Used in all my vehicles for years
Reviewed by Mike:
Maintenance
Reviewed by Dogman:
I use this oil in my '02 2500 Ram Diesel to protect that engine for the long haul. The 5.9L Cummins is the last of the "loud ones" for Dodge. I want to try for 750,000 to 1 million miles before it needs any real work put into it. That sound is one of the reasons that I bought it in the first placeI love how it runs and I get great longevity out of the oil. If you run a diesel you would be crazy to not try some in yours. Worth every penny!
Reviewed by rdj519:
I installed the bypass oil filter system when I bought it new. Oil sample every 7000 miles. This oil and system is the best thing I have ever done for my big truck. Only the best for my baby
Reviewed by Jack:
I have always run synthetic oil in everything, but since I bought my Duramax, I thought I'd try you product and filter. So far so good, I'll let you know in about 150000 miles.
Reviewed by obg:
Great stuff wouldn't use anything else.
Reviewed by REJ:
This is the only product that I can find that is recommended for my Eco Diesel and it performs as advertised.
Reviewed by Mike, 2017 Dodge Ecodiesel:
First time have used Amsoil diesel oil. So far so good. However I didn't notice much change in fuel economy after using Amsoil 5W40 SS diesel oil for my first oil change in this truck, in town driving. High way driving did show some improvement, all the way up to 30.2 mpg, previously had gotten 29 mpg. I think part of this is my motor is still breaking in as diesels take awhile to do so. Overall I am pleased & have used Amsoil in both of our vehicles going on 18 years.
Reviewed by Pinkpeaches10:
Perfect oil.
Reviewed by Doc Pat:
I use this on my 3 diesel trucks. 1985, 1994 and 2001 F 350.
Reviewed by JGD:
I am using this in my new F250 Diesel, as always Amsoil has created a superior product you can depend on. I can physically tell a difference just by using this oil. The truck runs so much better.
Reviewed by Jonathan:
I am rough on my trucks farm use hauling ext... Has 300k+ doesn't lose it burn a drop still run 25k between oil changes love my amsoil
Reviewed by Russell:
I was told it was it would help eliminate dust particles from the DEF system that build-up in an engine. It has helped with eliminate dust buildup in the engine significantly. Immediately after using the first time, many miles ago, I felt more power being produced from my engine. I'm a very satisfied customer.
Reviewed by Butch:
I have used Amsoil for 20 years. I like the extended oil change intervals, it saves me money and doesn't damage my equipment. I took oil samples and had them tested after 18,000 miles. They came back no wear and more mileage before changing. This was on a 1978 Dodge van with 180,000 miles. I currently use Amsoil in my 2006 Ford F350 6.0 diesel FX4 in all gear boxes, and 2012 Ford fusion. I am very satisfied with Amsoil performance.
Reviewed by Joe:
I use Amsoil in every combustion engine that I own. Vehicle, farm equipment, lawn mowers welding machine and generator. Never had a lubrication issue with any of them.
Best oil
on the market hands down!
Reviewed by Scott:
I believe in synthetics and Amsoil.
Reviewed by Doug:
love this product, but have nothing to compare it to because the last two new trucks I've purchased i change the motor oil and transmission fluid as soon as i get home. sold my 2007 GMC Classic Duramax 4X4 with 180,000 miles for over book price. To a mechanic. i could go farther but always change oil at 5,000
Reviewed by Jason:
I use this product in a 3/4 ton work truck.
Very high quality product.
Reviewed by Grandpy:
No worries
Reviewed by Super04FX4:
After trying several different synthetic diesel oils over the years...I have settle on AMSOIL as the best. I see consistently better cold starts and the extended change interval is a huge plus!
Reviewed by Ray:
I have used Amsoil 5w- 40 since I purchased my truck 8 years and 210,000 miles ago. The truck runs as good today as it did then.
Reviewed by GregM784:
Runs great, runs cooler, a product you can trust.
Reviewed by Tom:
I'm sold! I've used Amsoil products in all my vehicles for over 25 years. Engines run more quiet/smooth, better fuel mileage, and longer engine life. I recently convinced a friend to try Amsoil, they had an immediate 4-5 mph increase! What more can i say?!!
Reviewed by Duramax:
I have used amsoil in my 2008 and now my 2017 duramax. Love the reliability and superior quality of the oil.
Reviewed by Copper:
Been using this product for about a year I had noisy lifters on my truck using amsiol has Quiet them where I can hear them anymore Great product
Reviewed by REC:
I have found that using Aimsoil products I have added longevity and life to my vehicle. I drive around 1500-2000 miles per week.
Products service my vehicles mechanical parts awesome.
Reviewed by Zlob66:
Used in a 2005 GMC Sierra 2500 HD, have used Amsoil products exclusively since I purchasing the truck, will definitely continue using.
Reviewed by Tazman:
I use AMSOIL in my 2007 Dodge RAM 3500, my wife's 2013 Ford Edge, 3 Waverunners, and all of my power equipment. I have not experienced any issues with any of these applications. Warranties are not voided, and fuel mileage in both vehicles is improved compared to conventional oils.
My Dodge Ram has the Cummins 6.7 liter diesel with 268k miles. The truck is still purring like a kitten, and doesn't burn a lick of oil. I am still on the original transmission without any re-builds as of yet. (very uncommon for the Mopar trannies). I extend the oil change intervals to every 9k miles, even though the manual states not to extend. I have not witnessed much , if any fuel dilution in the
oil.
My Wife's Ford Edge has a mere 78k miles on it. I change the AMSOIL Premium oil in her car every 15k miles, even though the AMSOIL reference sheets state she could go 25k. I just like being careful.
I run the marine 10W30 in the Yamaha Waverunners and have smooth acceleration, without any vibration or oil burn.
Overall, I love the AMSOIL products and would recommend to anyone looking for a top end, fully synthetic, highly protective oil.
Reviewed by Kodiak:
My Diesel runs smoother and quieter
Reviewed by McKittrick:
I never knew you could see the difference in oil. I switched to amsoil a few months ago. I noticed easier starting in sub zero weather, and a slight increase in fuel mileage. I was running a synthetic before. Amazing.
Reviewed by celtic:
I became aware of And oil in 1985. I knew how good synthetic oil was as my older brother was a petroleum engineer and he declared that synthetic oil would soon be the dominant motor oil. I had my brother run some tests on a quart of And oil and he reported that the stuff was off the charts. He and I became long time customers. I have never had any type of engine failure due to poor oil performance.
Reviewed by Rosie:
Installed AMSOIL in my old Chev Diesel. Changed the filter every 5000 miles . Checked quality of oil each time. At 20000 miles the oil was still good. Amen. This was at 100000 miles and used a quart every 3000 miles .mwhrn traded atb441000 miles it used only 1/2 guard in 10000 miles . Had an old 99 suburban diesel bought used. Was up to 1 quart every 4500 miles when traded at 352000 miles.
Reviewed by Russ:
Great oil for my 2500 Jd
Reviewed by Bryce:
I've used this product as well as many other amsoil products in many trucks and pieces of equipment and they are superior to any other on the market. Much smoother running with lower temps and increased mileage.
Reviewed by Jay:
I use this oil in my dodge 2500 cummins and it works great. Lasts long.
Reviewed by DR:
Better fuel mileage
Reviewed by Nordy:
Love the protection and convenience of oil changes once a year. Saves money and time.
Reviewed by Cujo:
Duramax seams to like it, oil samples great @ 10000km, filter change and re sample @ 20000km!
Reviewed by sawdust:
I have used AMSOIL for over 30 years great stuff!
Reviewed by Charlie:
Only use the truck to tow keeps oil temp down
Reviewed by Bill:
The oil in my 199 F-250 SD with 7.3 diesel, bought new, use to get its oil changed every 3-5K miles for the first 6 oil changes. Then the switch was made to Amsoil Synthetic, with Amsoil oil filter. The oil still looks new after the first 3-4K miles and is changed every 10K miles. Although I have had no problem with this vehicle related to lubrication, the vehicle may be considered low mileage with 262,000 miles and o8il consumption has been greatly decreased. Love this oil.
Reviewed by Greg:
I have had Silverados with Duramax for daily use and towing a travel trailer. I change the oil at extended intervals using the Amsoil and have used this oil with confidence in all seasons and conditions around the country. Signature Series is the best!
Reviewed by Brennon:
Before using this product in a 2015 Silverado 2500 I had consumption of standard oil. Truck was using 1 quart of oil per 5000 miles. After switching to this product I have not experienced any consumption.
Reviewed by Smitty:
I have used this since the truck was new. 110,000 miles and it is running like new.
During the recent cold weather, it started right away and oil pressure was At recommended level. Great protection!
Reviewed by Mike:
2000 F250 7.3L TURBO!
Reviewed by Sixpack:
Engine oil, Quality
Reviewed by Chief:
I bought a 2001 F250 with 70,000 miles on it. After a couple of trips to a local quick oil change every 5000 miles at a cost of 150.00 I decided to try Amsoil diesel oil and am very glad I did .I use Amsoil diesel oil and filter I have extended the oil changes to yearly this by itself is a substantial cost savings the truck runs great and averages 16 mpg. It now has almost 250,000 miles on it and counting
Reviewed by Clark:
This oil is all that it says it is.
Reviewed by Andy Frame:
The only oil I trust for my twin turbo Duramax
Reviewed by Bob:
I've been using Amsoil motor oil in my 2007 Ford F350 diesel now for past 9 years. Each time I change the oil, which is every 5000 to 6000 miles, I also take an oil sample for lab analysis. The lab reports have always good. No appreciable wear, and it's viscosity after 6000 miles is well within acceptable ranges. Internal parts of the engine remain extremely clean, no deposits or sludge buildup.
I also use Amsoil XL motor oil in my 2016 Subaru Outback, and before that, a 2010 Forester and never had any engine problems.
I am extremely sattisfied with all their products, from engine oils to gear lubes, which I have been using in my F350 for 9 years.
Reviewed by Armory racing products:
This oil quietnes down all Diesel engines and last long with no signs of thermal breakdwn
Reviewed by Rosco:
I use this oil in my 7.3 and never have a problem with cold starts even with the truck having 200K. Truck runs great with this oil and I have lower oil temps and smoother idle.
Reviewed by Gee:
I use AMSOIL in everything I own.
Reviewed by Teddy:
Amsoil is the best oil products out there. I run heavy loads with my truck and travel a lot. I get great mileage out this oil and it holds up to the extreme temperatures here.
Reviewed by noname:
I use this in a 2000 7.3 Ford Diesel. Motor has over 200,000 miles and still runs like a top. I will continue using Amsoil products; my engines run great and stand up very well with their products.
Reviewed by Wumba:
Been using this in my diesel truck for years with never a problem. Online ordering was quick and easy!
Reviewed by Randy:
This is my second Duramax and AMSOIL is all I use in all my vehicles.
Reviewed by Scott:
used in a 6.0 Powerstroke. Probably the most demanding motor of oil because of the design of the 6.0 Powerstroke and the use of the oil to hydraulicly power the injectors.
Reviewed by MtnDsrtMn:
My truck just keeps running smoothly. I TRUST Amsoil.
Reviewed by Ryan:
I had this oil in my L5P Diuramax for 5,000 miles. I have never heard such a loud clicking noise come from this motors till I put this oil in. Will never use again. Oil consumption went from zero to adding a half quart every 1500 miles with this oil. Could not wait to get it out of my engine.
Reviewed by Cptn_Jon:
I bought a new GMC 3500 Duramax in 2005. The first OIL change was AMSOIL Max Duty Diesel pool 15W-40. With this OIL I only need to change OIL once a year (AMSOIL recommends once every 20000 miles) and I only have 10k per year. The OIL is costly but with the perfered fostered card ($20.00 per year) you save in the long run.
Reviewed by Lance:
Very affordable and an excellent product!
Reviewed by 1:
Great
Reviewed by Jr:
Use Amsoil in all my vehicles and toys.
Reviewed by WIll the pill:
I will continue to use this product.
Reviewed by DarwinG:
Always been a fan.
Reviewed by The Butcher:
Love amsoil! Ships right to my door and is always quick to arrive. It's all that's been run in my Cummins since it had 60,000. I am at 280,000 and counting. Amsoil speaks for itself!
Reviewed by Mr. Stevens:
I've been using this oil for 25years . Would never stop.
Reviewed by Agent:
Engine
Reviewed by Spike:
Since using Signature Series Amsoil in my F350 7.3 my truck is quieter and my mileage has increased. This oil is a miracle, I've been working on vehicles for over 40 years and this product has given me the best results of any lubricant ever.
Reviewed by Bill:
In addition to long interval oil changes my oil has to get me through all four seasons especially the cold North Eastern winters. I've tried many brands of oil and Amsoil Signature Series has proven to be the best. Cold starts no longer an issue if I forget to plug in my truck overnight or just leave it off for a shift at work. I really like this oil and trust Amsoil products.
Reviewed by Bob the Old Engineer:
Used the diesel oil in my bosses 2004 Chevy 3/4 ton 2500 PU,After this demo,will use in all equipment
Reviewed by Dieseldad:
Diesel motorhome and 2004 Ford PSD.
1998 Jeep Wrangler and 2015 Jeep Cherokee.
All lubes in all my cars are Amsoil.
I will use nothing else.
Reviewed by
Terry:
Great product, will use each time I change oil
Reviewed by Duramax:
This is the best oil I have ever used this oil makes every other oil look like valve grinding compound
Reviewed by Tattooedguy:
Amsoil is a great product, great service, I use there products in my 2016 dodge diesel
Reviewed by Dusty:
Best diesel oil on the market. Wouldn't be caught using anything else. Read the specs.
Reviewed by Willie:
I've used this oil for a while now and all I can say is I love it. My truck runs smoother and doesn't burn oil when I'm pulling.
Reviewed by Blake:
I purchase this oil for the soot contamination, fuel economy gains and the wear additive package. I can tell my Duramax doesn't "tick" anymore and the fuel economy is much better. I can also go longer between changes. All in all a great product.
Reviewed by Ski:
At first the motor was running smooth. I was excited and thought I had the best oil on the market. A couple if months later I can see the final results. Amsoil is good as like the rest of syn. Oil is. For deisels they need to make a thicker oil for Arizona then they will profected it. Im asking them to provide the research because I believe they could be the best.
Reviewed by Denali 16:
Can't be more happy with the oil I've been running it for almost 10 years your missing out on the quality of this oil if your not using it
Reviewed by Nate:
Engine runs quiter and seem to get better fuel mileage. Very happy with the oil product.
Reviewed by Chris:
I like this oil in my 99 ford power stroke. Holds up well.
Reviewed by Mr.AH:
Use this oil in a tow vehicle never loses a drop of oil in 5000 miles
Reviewed by Adam:
I run this stuff in my Duramax and have since I bought it in 12'. It holds up to whatever I put the truck through. Best bang for the buck on the market.
Reviewed by Gerald Barber:
Although I've never use this oil before I'm confident I'll love it as I've been useing it in my M/c for years ! You just can't go wrong with amsoil!
Reviewed by Rosco:
Being a new customer to Amsoil, I've read lots of reviews and spoke with Amsoil Tech several times, and lots of satisfied customers before making the switch. I'm still a few thousand miles away before the first oil change. This is with Amsoil oil filter. With all the above sad, I'm very satisfied with the product and the technicians.
Reviewed by Loren from pa:
Have a 1996 3500 5 speed and have used amsoil in everything since it has had 15,000 and it now has 358,000 with no major breakdown
Reviewed by No:
It kept the engine cool. It doesn't break down.
Reviewed by Greentown Joe:
My mileage increased a bit. The engine runs a lot smother. I plan on keeping my truck for many years and this oil is go to oil.
Reviewed by Highheat71:
Best lube oil for my one ton Ram 3500. But not without the Amsoil EA filter.
Reviewed by Cliff:
I use 15 40 in any vehicle I have which includes my tractors, lawn mowers.
Reviewed by Dolly:
I drive a lot of miles in a short period of time and I don't have time to change oil every 5 to 6ooo miles
Reviewed by Hotshot John:
I completely switched my Dodge Ramsey 3500 to Amsoil at 140000 miles. Started out doing complete oil changes every 20k with just filter at 10k mark. Decided to have an oil analysis done. By time I have next sample tested it will be at 30k miles on this oil change. Saves money and downtime.
Reviewed by Tk:
Perfect product
Reviewed by Studentofbudo:
This is an exceptional oil. Definitely made my ol' 6.5 detroit run smoother and helped with mileage!
Reviewed by Yelly:
For my Duramax diesel
Canada
United States
Max Duty 15w-40 Diesel Oil = Good Stuff
I am relatively new to Amsoil but have and have both Duramax and Cummins - currently have a L5P Duramax with an Amsoil Duel Bypass oil filter set up which I did not have on my previous Duramax. Thus, apples to apples may not be in the following:
1. Blackstone reports come back much better than with the Rotella T-6 I was using in the prior '15 Duramax actually with about 7500 vs 5000 miles.
I got some usage w/Rotella T6.
2. A bit of oil usage with the Rotella t-6 but absolutely none with the Amsoil.
Repeat not apples to apples exactly as different engines and the L%P has a duel bypass set up on it.