Customer Ratings & Reviews

I was recommended this product from a good friend who said it made his truck run smoother and more responsive. I began adding the additive to my gas at every fill-up and definitely noticed within one tank that the product does exactly what I expected. I highly recommend this product for anyone with a diesel engine and will continue to buy this product from now on. I will be referring my friends as well.

I run this in my second gen Cummins year round. It smokes less and runs smoother than others I've used. I recommend this to anyone driving a diesel. I would be led to believe less smoke is easier on emissions systems but I l

Stuff works really good little bit pricey though

Works as intended

Improved acceleration. Increased mpg. Easy starting.

As far as I can tell, 4-1 Diesel Treatment seems to work well as my engine runs smother after treatment. I have a 55 gal tank and use one 16 oz bottle with every other fill up. The reason for the 3 Star rating is due to the fact that none of the Amsoil retailers carry this product, and I have to pay EXTREMELY high shipping costs when ordering direct. I sent an email to Amsoil Customer service and all they do is refer me the "Find Amsoil Near You" on the website

Keeps fuel system lubricated

I bought this diesel truck in 2017 new off the lot in Houston, Texas. Ran 500 miles break in with the factory oil then changed to Amsoil. First tank of diesel had this additive and I've used this additive with every tank of diesel. Just went over 211,001 miles and have never had any issues with fuel, that crazy CP4 fuel pump or any injector issues. Truck runs like a new one even with the miles on it today. My mechanic tells me that the only reason I've not had a pump failure is because I've been using the additive.

Perfect for my F-250 7.3!

210,545 miles NO CP4 failure because of this product! Diesel mechanic tried to sell me on a "disaster prevention kit" until he heard I've been using the product from the first tank of diesel.

I use this all year round in my truck, tractors and mowers. I have never had a single problem. Don't use #1 in the winter I just use 4-in-1.

Just starting using Amsoil 4-1 Diesel fuel treatment based on social media recommendations. Have gone through 3 tanks, every other fill up, and seems my Cummings 6.7 gen-4 with 120k is running a little smoother. However no news is good news in this case.

Product works as should

Great product! Noticed better cold starts, fuel economy, and power.

This is a great all in one product. One bottle works for all my needs including the annual trip to Wyoming in freezing climate.

My truck got some bad fuel (water) and my injectors suffered, I kept using this 4in1 to help lubricate the pump and injectors in hopes of extending their life, was constant injector performance faults. Took about 1 month of continuous use but the faults are gone. I also started to use this product on all my construction machines, especially like that it has the anti gel additive, it’s helped me a few times.

I have only used a single bottle so far. However, having said that it works. I live in a very cold climate and it is doing its job.

Great product I fill like my truck runs better on this and I don’t have to worry about the fuel gelling on me.

Never have had any problems with injectors clogging up. Can rely on consistent power.

Four stars only because I wasn't able to rate it any lower than -20 degrees Fahrenheit. Diesel was unblended #2 with a sudden cold snap arriving and used the additive without starting or running issues on a ungaraged diesel over a three day period.