Product Reviewed: 10W-40 Synthetic Formula 4-Stroke Marine Oil (WCF)
Current Rating: 4.88 out of 5 stars
Votes & Reviews: 45 vote(s) and 49 user reviews.
Reviewed by James: 
I use this great lube oil for my 1990 Cruisers Esprit with twin Crusader 350's. I am never disappointed with this synthetic, even though they were designed for straight SAE 40. They run smooth and oil pressures are spot on.
Reviewed by Robert:
Fantastic no issues with this product will buy again and recommend it
Thanks
Reviewed by Andres:
Perfect oil
Reviewed by Bryan:
Great value
Reviewed by Triston:
Great product, love it
Reviewed by Russell:
Use Amzoil in all my cars and motorcycles, jetski's etc.
Never had an oil related failure.
Will continue to trust Amzoil.
Reviewed by Robert:
Great stuff. Boat runs way better.
Reviewed by Brian:
Great product when two outboards cost 50k you use the best product possible. Please make filters for yamaha outboards
Reviewed by Vic:
I recently started using Amsoil Marine in our Yamaha Jet Boat. With the boat being 6 years old, I immediately notice a quieter ride and was most impressed by the 5-7% thrust improvement (3-5mph). We will be using it in our jet skis next
Reviewed by RMC:
Excellent outboard motor oil, engine runs smoother and quit with this oil. I would recommend this product for all outboard motor owners. Best product out there! I live in Hawaii and I never got any free shipping or any free products. Thanks!
Reviewed by Bobby:
I have been using this in my Yamaha 150 4 stroke for over 10 years. I recently replaced the balancer and had the opportunity to inspect the engine internally from the bottom end. I observed absolutely zero wear on visible internal engine parts and the engine was so clean inside it looked brand new!
Reviewed by West Coast Boater:
Use it on both my Yamaha 2016 115 hp and 2017 9.9 high thrust motors.
Reviewed by Tomace:
Keep the motor cool and quiet
Reviewed by Chris:
Just recently bought a chaparral SSI sport bowrider boat took it out twice and got 47 miles per hour. change the oil to amsoil 10w 30 for boats take it back to the lake and ran it hard and got a solid 50 miles per hour.
Reviewed by Reeling:
I use Amsoil in my boat for the last three years. The engine seems more quiet and the oil level stays at the same level throughout the boating season.
Reviewed by Chris:
I bought a Seadoo GTR 215 supercharged unit and was looking for oil to complete an oil change. I've had great success with Amsoil in the past in sleds and atvs so I wanted to use in my Seadoo. I had read mixed reviews about using the Amsoil Synthetic marine oil in the supercharged skis due to supercharger clutch slip. But so far I've had no issues after approx 12 hours of riding.
Reviewed by Bob:
We use this product for a 60HP Mercury 4-stroke outboard motor. Love the product, and it is a great value also!
Reviewed by Millerlite66:
I run this oil in a 1988 Glastron. I'm the second owner. I have used the 10w40 Marine oil for the 18 years I have owned this boat. It has a 7.4 liter GM big block in it . I have never had an engine problem that had to do with lubrication. Just sayin.
Reviewed by Mitchell:
Can't tell the difference.
Reviewed by Louie:
Oil I could trust running offshore
Reviewed by Mismo Titan:
We run our sea doos hard and this oil has never let us down. For supercharged skis there are no friction modifiers and it's JASO MA2 which is safe for our superchargers. I've been running amsoil in all my products for a while now and won't run anything else.
Reviewed by Jeff:
Good product, quick delivery, nice website, I'm a fan of Amsoil.
Reviewed by Reggie:
Developed for Outboards; oil is cleaner after use than regular oil
Reviewed by Bobo0415:
Better than Mobile 1. Increased top end, engine runs more smooth at idle. Don't waste your time buying oil from the outboard manufactures, over priced and over rated. Amsoil exceeds Suzuki requirements and will not void warranty. Bought a case, saved on the shipping.
Reviewed by DonV:
This was my first oil change on my new outboard. I really never considered any other oil. I also used this same oil on the last 4-stroke outboard I had and it performed perfectly.
Reviewed by Showman:
I started using amsoil in my Yamaha because I did not have hour meter to keep track of hours thinking amsoils superior oil would give me some forgiveness if I went a little over recommend hours. I added hour meter, will still use amsoil under preferred customer plan.
Reviewed by Trotline:
I use this in my 50hp 4- stroke and you could immediately tell a difference. It ran much smoother and quieter.
Reviewed by Mike:
Great marine oil. Use it in the boat and jetskis.
Reviewed by mdd:
I've added this to my marine inboard motor and seems to be running very well
Reviewed by John:
Outstanding product...
Reviewed by John R.:
I have used the 10w40 Marine oil in my Yamaha Waverunner for awhile and to date just great results.
Reviewed by John R.:
I have used the 10w40 Marine oil in my Yamaha Waverunner for awhile and to date just great results.
Reviewed by Paul - boater:
Installed in both of my 8.1L Mercruuser engines on my 40' Boat. Also going in my generator. Hope to get the advertized results.
Reviewed by Reg:
I have ued this in my 115 mercury efi fourstroke and also my 150 efi fourstroke. Now I use it in my Mercury 225 Verado. Best oil to use here in Canada . No more hard starting when the température gets down close to freezing and a great remplacement for Mercury 25-40 semi synthétique oil.
Reviewed by R:
I like the product, oil seems to be better then YamaLube, Stays clear longer, while YamaLube becomes non transparent and dark grey almost black within 10 hrs. Have AmsOil in high RPM SVHO engine for 35 hrs now and its
still clear and light yellow color.
However overall purchasing experience was less the pleasant.
First, even though the address was correct, they did not ship on time because they could not read the address properly, then the courier didn't know what to do with the package.
So because of that it unnecessary took long time to receive the product.
Reviewed by Dennis:
Works great in my supercharged Sea-Doo. No issues with supercharger slipping, motor runs very smoothly. Will continue to use this.
Reviewed by Crusiers inc:
I use this oil in my 7.4 liter mercrusier motor. Now Amsoil and Mercrusier recommended that I use the 20w 40 synthetic blend. But I wanted full synthetic. This oil is AWESOME!
Reviewed by Lou:
Have always used the 10w-40 and 10w-30 marine 4 stroke in my outboard and wave runner engines. Very confident that it holds up well to the high revs.
Reviewed by MrEd:
I use Amsoil in my:
2008 M-Benz V-6 diesel (meets the 229.51 spec.);
2017 Subaru 2.5 normally aspirated 4 cylinder boxer (0W-20 Signature Series);
2013 Yamaha 90 hp outboard;
1999 Honda V-2 10kw generator;
pressure washer, and lawn mower.
I change oil in all these motors once a year, along with an Amsoil filter for the Forester.
I switched from M____ products to Amsoil after I personally compared the specs for 5 quality motor oils, including the "Subaru" oil (actually Idemitsu Oil) and found that Amsoil matched or was better in most of the parameters on all the oils, particularly the NOACK value (for volatility or "boiling off".) I was
especially interested in the 0W-20 values, since I had a chance to choose a specific oil to use in the new Forester for its life. I found that there was a huge NOACK difference between Amsoil and the Subaru/Idemitsu oil. No doubt that is why Subaru recommends a 6,000 oil change interval, and Amsoil Signature Series is at 25,000 miles. None of the other oils matched Amsoil's NOACK value. That comparison convinced me. At 500 miles I drained the Subaru/Idemitsu oil and switched to Amsoil Signature Series, and changed it again at 6,000 miles and am now on a yearly change cycle, since I average between 10,000 and 13,000 miles a year. Cheaper and better - a no brainer.
Reviewed by Don the Biker:
AMSOIL is the only engine oil I will use in my vehicles, motorcycle, and outboard motor. It improves the gas mileage on my Victory motorcycle by over 10% compared to OEM synthetic oil. That convinces me that there synthetic oil reduces engine friction and should help the engine last longer.
Reviewed by Daniel:
Best four the marine motor, always I used to my cruiser and bow rider, awesome performance
Reviewed by DANIEL:
Only oil my Outboards will ever see. One great oil
Reviewed by James:
I use this product in a 2013 mercury 150hp 4 stroke outboard. It runs great with no issues. Living in the northeast our season is short so I can only get about 75 hrs of use. My only issue is that you do not make an oil filter for this engine.
Reviewed by Brbstafford:
Have this in my new Waverunners after break in for winter storage.
Reviewed by Brian:
Have this in my new Waverunners after break in for winter storage.
Reviewed by Brad:
Outboard
Reviewed by Flattop:
I thought I'd try Amsoil Marine 10W-40 in my 23ft I/O that has a GM 350 CID engine. After changing the oil it felt like the engine had gained 30-40 HP. It gets on plane easier, revs faster, and runs as cool or cooler that the 15W-40 diesel oil That was recommended by the marina mechanic. Additionally the oil seems to stay cleaner longer. I just can't see a down side to this oil. It's all good. Pulls my grandchildren on their tubes and skis easier and gets up to speed faster even with a load. Great product.
Reviewed by Jeff:
I ran this in my mercury optimax 125. It ran cleaner and smoother than when running on the mercury oil!
Canada
United States
My first boat. Amsoil is my only choice.
This is my first boat. It has a Yamaha 175hp SHO 4-Stroke. I have Amsoil in everything I own. After the breakin hours passed. I replaced everything with Amsoil. Motor,lower unit and bearing grease. It's the only oil for me. Always a Great choice.