Product Reviewed: Signature Series Max-Duty Synthetic CK-4 Diesel Oil 5W-40 (DEO)
Current Rating: 4.87 out of 5 stars
Votes & Reviews: 204 vote(s) and 332 user reviews.
Reviewed by Ron: 
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.
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 Mud Creek Ranch:
Love this product, use it in both of my diesel vehicles religiously! Use it in my MF 300 Dozer as well, use Amsoil in my gas engines as well on the ranch.
Reviewed by G513:
Really haven't noticed any real benefit over cheaper options. The cost is a major problem.
Reviewed by James:
This amsoil does wonder's with my 2010 6.4 F250
Didn't change my oil tell 14k miles had an oil analyze at black labs came back great they said it looked better them most 6.4 diesel at 5k miles and told me they couldn't wait tell another 14k miles to see what it looks like
Reviewed by Matt Z.:
I have been using Amsoil in this truck since I purchased it, it turned 210,000 miles. I have averaged 17.9 mpg over the life of the truck. It has regularly towed 17k plus. These fluids are spot on!
Reviewed by Gregory:
I switched to this oil from 5w/30 Series 3000
Because of price.
Reviewed by
7Trumpets 42:
I am having regular oil analysis with each 10K mile change. Engine metals are lower than average for the V-M 3. 0. I couldn't be happier with this signature Amsoil product!
Reviewed by Hauss:
I've been using Amsoil lubricants for decades. I'm loyal to the brand. I've been with Amsoil through the good times, and one of their bad times (back in the eighties). I've run Amsoil in motorcycles, cars, trucks, boats, high-performance engines, and factory daily drivers. I have extensive experience in engine machining/building, and I've seen, first hand, how Amsoil provides performance and
durability to engines that push their design limits.
Recently I bought a 2017 F250 with the PowerStroke diesel, and I got to reading about the particulate filters, and how oils not approved by Ford could cause premature clogging of the DPF, and possibly void the manufacturers warranty. Oils manufactured to the CK-4 spec initially resulted in premature wear in 2017 PowerStroke engines, so Ford released their own specification, WSS-M2C171-F1, and instructed owners to run CJ-4 oils until approved CK-4's were available. Since then several products have been approved by Ford for use in PowerStrokes, but concerned about the performance of the available CK-4 oils, and curious about how Amsoil's Signature Series Max-Duty Diesel Engine Oil compared to them, I submitted a couple of samples to the guy who runs the 540 RAT Blog for testing. The Amsoil product tested superior to all others tested to date, beat only by another of Amsoil's own CI-4 spec diesel engine oil. I wasn't surprised by that, based on my
experience, but I was surprised to see a conventional CK-4 oil approved by Ford that also meets WSS-M2C171-F1, performed as well as Amsoil's Sig Series Max-Duty, and costs about half what Amsoil's product does. I would love for Amsoil to explain why their product is still superior to that competing product, even though they performed so similarly in 540 Rat's test. At thirteen quarts, half the price is quite a savings. Is it really worth the price?
Reviewed by Rock:
This product is great. I have ran this product the last 15,000 miles. My trucks starts smooth after sitting for a week in the cold weather of northern NM. Never misses a beat either. Would recommend to any diesel owner out there.
Reviewed by RAV:
Since 2010 I've
been using Amsoil fluids and filters in my Dodge Ram 2500 Cummins Diesel and as a result, have had no engine or transmission failures.
The diesel engine oil & filter are both 25,000 mile change frequency; Amsoil does cost more, but you'll save money in the long run with zero failures and extended periods between scheduled maintenance.
I also ran Amsoil transmission fluid in the same truck for 70,000+ miles with no slippage, and always witness iyuyreliable, positively locked shifts.
Reviewed by Bam Bam:
I drive 114 miles a day for work
Reviewed by Bentley:
Feels like my trtuck runs a lot smoother
Reviewed by Pete:
Love using the best protection available for my Chevy 6.6 that I work hard everyday and with 123,000 not a single hiccup.
Reviewed by Chuck:
I would and do buy it all the time
Reviewed by Chuck:
😉
Reviewed by Dave:
Engine ran cooler in summer by five degrees with Amsoil. -25C starts not an issue, even when I forgot to plug in.
Reviewed by Sky Pilot:
I use the Signature Series Max-Duty Synthetic Diesel Oil 5W-40 in my 2004 Dodge Ram 2500 4x4. I following the recommended drain interval so I end up changing it out yearly before I reach the kilometer limit. I do mostly highway driving. I don't think I've ever had to top it up between changes either. Great cold weather starting properties for winters in Alberta.
Reviewed by Stan H.:
I have used amsoil for years in my 6.7 cummins diesel and it has never failed to deliver . I recently swithed to the new 6x signature 5W-40 and I noticed that my oil pressure went up one pound and my fuel mileage went up one mile per hour also . Now to some this may not be a big deal but it adds up over time and that it is giving me better pressure at the same time only goes toward helping to further protect my engine. with the increased wear protection quality and potential I look forward to many more years of faithful performance from amsoil oil just like this .
Reviewed by Greg:
I have used this oil in my Silverado Duramax in cold weather and it helps with cold starts and driveability during long warm-up time. The engine gets lubrication almost immediately upon startup and sounds like it is running on a summer day. Amsoil is the best!
Reviewed by Josh:
This is a high mileage truck 350,000 km it starts great in cold weather and a faster clean start
Reviewed by Phil:
I have used and only used Amsoil in my 2004 Dodge 2500 with the 5.9 HO Cummins. The wear protection and the oil life is amazing.
Reviewed by Airstreamer Joe:
I have been using
AMSOIL in my GM tow trucks sense 2000. I have out over 300,000 miles on 3 GM pickup trucks, while towing my 34' Airstream in all the lower 48 states, 2 summers in Alaska, and all but one Canadian Provence's.
I put a dual filter kit on my 2000 GMC 2500 gas truck, and switched to AMSOIL when it had 3000 miles on it. I set up an oil diagnosis program at a 3rd party lab. I setup a system of monitoring my oil every 3 months, but only changing it one time per year (usually about 20,000 miles mostly towing the 10,000 pound Airstream). I would change the full flow filter 2 times per year, and the bypass filter one time per year. I bib not get a recommendation to change the oil from the lab in 3 years. I had no problems with the engine in the 125,000 miles I put on it.
I traded the truck for a 2004 GMC 2500 diesel truck, and went through the same setup of the oil change system using AMSOIL Diesel oil. I put 122,000 miles on that truck, with no oil related problems. I sold the truck to a friend and bought a
2015 Chevy 3500 diesel truck, and you guessed it, it has the same oil system setup on it. It now has 30,000 miles with no problems to date. The 2004 truck I sold to my friend is still using AMSOIL, and changing it one time per year. It is still being used to tow a travel trailer, but I do not know how many miles it has on it now.
I would recommend AMSOIL and their Dual Filter System to anyone that puts tough miles on their truck every year.
Reviewed by Mike:
When I start my engine at -35 degres celcius it runs smoothly.
Reviewed by Mike:
When I start my engine at -35 degres celcius it runs smoothly.
Reviewed by Mike:
I switched my 2016 Ford 6.7 diesel oil @ 60K miles...with 126K on it now and driving 100K per year towing heavy loads"half the miles". I trust this engine oil above all others and expect to get at least 500K on the engine before I buy another one!!!!!
Reviewed by Jamie:
This oil flows pretty good when the temperature gets down to zero.
Reviewed by Wild Bill:
Just hit the 40K mark in a 2016 EcoDiesel. Only run the best oil and no worrys. Have used AmsOil in all my vehicles, boats, and ATVs for over 10 tens with NO engine problems.
Reviewed by Doubleplay7:
This product is a good product that is good for a wide range of diesels. I run this in a 02 Ford F-250 and will be running it in a new Ram 2500.
Reviewed by Amsoil Believer:
Simply put, Amsoil is the only product I will use on all my vehicles, if I can help it. Have been using Amsoil since my first FORD SVT LIGHTNING in 1993. I am using the diesel oils for my foreign vehicle, a Ford Everest, that's made in Asia. I have also used the diesel oil in my farm vehicles, a Dodge Ram 3500, and other diesel engines. You can't go wrong with AMSOIL.
Reviewed by Z:
Use in my tuned 2006 2500 Dodge Ram Laramie Mega Cab. Many miles and still runs like champ!
Reviewed by Eric:
I have been using Amsoil for a very long time. I love when they come out with enhancements like this new diesel oil. I will take all the protection I can't get.
Reviewed by Al:
My grandson uses this this in his dodge guide truck, he is a fishing and hunting guide in the Lake of the Woods Nestor Falls, Ontario area. He also use AMSOIL in his guide boat and I use AMSOIL in all of my vehicles including boats. I have been using AMSOIL products since about 1983 and as far as I am concerned there is nothing better. I recently changed my 2012 corvette from Mobil 1 to AMSOIL signature 0W-30.
Reviewed by Slick Nick:
I'm using it for year in my semi and never left me down. Great quality lubricants.
Reviewed by Ode:
I use this in my ram 1500 ecodiesel. It performs well. No usage with 49k miles.
Reviewed by Moparguy:
Awesome product. Long time amsoil user. The products just get better!
Reviewed by Greg:
The ONLY I will put in my '16 Ram 3500 Dorsal!
Reviewed by $ilver6_7_cummins:
I started using Amsoil about a year and a half ago. It is now all I run. Wether it be in my diesel truck, snow mobile or boat, Amsoil has the product for it!
Reviewed by Kissoondath Rovin:
Arms oil products is great, the experience I had with the signature series oil I have used it on 2 of my 2016 &2017 , 6.7 diesel and they both have burnt the oil , I had to add oil A quart after driving 16000 miles , now I do all my oil change at 15000 miles to be on the safe side , the arms oil is a much durable oil compared to other oil it there I will continue using the heavy duty for marine diesel and gasoline oil
Reviewed by Steve:
Excellent at every point.
Reviewed by The real noble:
Use Amsoil synthetics with bypass filtration in my 2012 Ram 3500 Cummims. Oil analysis has got me over 20,000 kms between oil changes. Highly recommended
Reviewed by Ray:
Always change my oil every 6 months. I have only 65K and mainly tow a 30 foot trailer in the summer months. I use Amsoil, engine oil, transmission fluid, differential oil, and filters. Great products.
Reviewed by Ron:
I've been using Amsoil for 15 years now. Diesels, and family's automobiles, utvs, boats, and more. I know i can trust Amsoil, and have extended the life of all my equipment. Great oil, filters, and much more.
Reviewed by Fordfan:
excellent
Reviewed by Cooory Ed:
Great oil
I run amsoil in everything
Reviewed by Muleboy:
Swapped my Duramax diesel over to this oil. I want this vehicle to last for years so I am going to use the best oil I can. I plan on doing oil analysis as well to get the most out of this product.
Reviewed by Kyle:
I have four dodge diesels and a cat powered welding machine and I run this oil year round with zero issues. I do oil changes every 25000kms.
Reviewed by Pat:
I use this oil in my 2014 Dodge Ram EcoDiesel. Amsoil updated the oil from 5W-40 to 10W-40 based on Dodge recommendations. Great oil.
Reviewed by Jon Driver:
Under heavy usage and need peace of mind
Reviewed by Chris:
My engine is still running and since I can't see inside it, it must be working.
Reviewed by SG:
Dumped class 3 synthetic rosella t6 for a true synthetic class 4 PAO Amsoil Sig Series 5w-40. Turbo Diesel is running smoother, quieter, cooler and 2-3 mpg boost! Worth the money!
Reviewed by Rick Wysynski:
I was a Royal Purple junkie since it was the only synthetic available to me where I live and got it free. It worked great in my gas truck and other gas vehicles. I switched to Amsoil since I purchased a diesel truck and became a Preferred Customer. Really like that part !!!
The truck runs much better and accelerates better than the Ford oils that were in it and oil change at 25,000 miles is a nice $$
saving feature. I will switch to the new synthetic 5-40 on the next oil change and then extended changes past 25,000 would be nice. I monitor all things done to my truck and log it.
Put 9,000 mikes on the truck in less than 4 months and excellent results !!!
Reviewed by Phil in Tulsa:
I've been using AMSOIL heavy duty diesel oil for years and it has performed extremely well. This year I decided to try the Signature Series Max-Duty and was I amazed. I didn't believe I could tell the difference but the engine runs even smoother. I tow trailers with my truck and protecting the engine is paramount to reduce wear and lengthen the life and this oil delivers.
Reviewed by Kelley:
I use this oil in my skid loaders as well as heavy duty pickups pulling heavy loads
daily.
I have been sold for many years after I had 6.0 diesel that dumped all the oil and the only thing that saved the motor was this product.
All the shop had to replace was head gaskets
Reviewed by patrick:
In my Excursion Diesel 250,000 miles
Reviewed by F450:
First, I'll say that I love Amsoil. I run Amsoil in every engine/transmission/differential/etc I own. I'm not sure about this new oil. My oil temp in a Ford 6.7 Powerstroke usually runs about 203 degrees (previous version of Amsoil diesel oil). With this new oil (December it might have come out???) I'm running 7-10 degrees hotter on average. I'll probably try one more oil change with it and if it still runs hotter, I'll have to find another brand.
Reviewed by Dave:
I am astonished at the engine oil life provided by this oil, compared to the Mobil synthetic I used previously. I'm at 14000 km, 80% city, and the computer is telling me I still have 20% oil life. Previously I would get to about 10k and be looking to change. Admittedly I changed to Wix filter at the same time from Oem, so not a 100 % true comparison. Winter, with more idling, will be the real test. Engine seems to be running cooler even in 30C weather- that's hot for us!
Reviewed by Nimble:
Use it a 09 Chevy Duramax, starts great even if it hits 0 or below
Reviewed by John R:
I currently use this product on my 2016 Ram EcoDiesel with no issues and have use the previous 5W40 diesel product on previous diesel pick up trucks and heavy-duty equipment with no complaints. Thank you Amsoil.
Reviewed by Matt:
Engine ,primary and transmission fluid for my fxstdi.
Reviewed by jobu:
i have used Amsoil in the past in a 6.0 powerstroke and didn't really see much difference, tried it again in my 6.7 powerstroke and love it. The motor starts and runs smoother and helped with the mpg
Reviewed by Ryan:
My son uses Amsoil in his 2011 Ford F350. He has many mods on his truck. This is the only oil that he trust.
Reviewed by Rob:
I put this in my Kabota BX25
I was hoping it would quiet the motor and make for easy starting on cold inter days.
It did quite the motor a lot.
Started with no issues.
Reviewed by Big Frank:
New 2017 ford diesel. Outstanding oil. Highly recommend it. Would only use this oil in my new Diesel engine It is so high tech
Reviewed by None:
Ran for 8 thousand miles & love it so far
Reviewed by Dimonic:
I like to do my own oil changes, and avoid all the "additional" services the dealer offers.
Reviewed by Cumminswitit:
My truck and I love this stuff. I run it for a year between changes and love it. Best oil out there
Reviewed by elkoholic:
Truck is used for hauling horses.
Reviewed by Petro:
I use Ams oil in every application of my truck and never have I been let down
Reviewed by MURF:
IN A DODGE SPRINTER
Reviewed by 4B RANCH:
I have three diesel trucks and five diesel tractors, and all are serviced with Amsoil products. Besides extended oil changes, my engines stay clean and trouble free. I would never consider using anything else.
Reviewed by Randy:
I have used this oil for over 18 years in a 7.3 diesel ford-350 4x4 and have had great performance in using it .The engine doesn't have to work as hard with Amsoil synthetic oil 5-40w it runs cooler and less RPMs for the same speed as other oils . If you're not using Amsoil synthetic oils in your engine and truck and or other motor vechicle your missing out on the best performance your motor Vechicles can give you ..
Reviewed by engr:
looks good. I will need more time to fully evaluate it.
Reviewed by truckguy12:
Premium oil for a premium price. Works out in the long run for me with extended drain intervals. I use it in all my diesel business trucks.
Reviewed by Trev:
I use amsoil in all my vehicles, even my lawn mower. This stuff is the bomb, less oil pressure due to better flow, and smother running etc...
Canada
United States
All I use
Been using Amsoil diesel oil and Ea08 filters every 15k since the truck turned 30k miles. Have 276k now.
Could do a longer interval with testing