ATS 505CRO Oil Treatment: What It Does and Who Actually Needs It

ATS 505CRO is a pour-in engine oil treatment made by ATS Chemical, a company based in Albuquerque, New Mexico. The company was founded by Bernie Thompson, who has a background in aerospace engineering. 

The product works by chemically breaking down carbon deposits and sludge that build up on internal engine parts over time. It targets specific problem areas like piston rings, lifters, camshaft phasers, oil control valves, and timing chain tensioners. 

When those parts get coated in carbon or sludge, they can stick or stop working properly. The idea is that cleaning them out restores normal function, reduces oil consumption, and improves overall engine performance.

The product works in gasoline and diesel engines. Although ATS Chemical markets it to both everyday drivers and professional shops, the packaging labels it “FOR PROFESSIONAL USE ONLY.”  It’s fair to assume that this is not a general-purpose additive you throw in at every oil change.

Who Should Actually Use It

505CRO is built for engines that are already having problems, specifically older or high-mileage engines with significant carbon buildup. It is not a preventative product. 

Using it on a newer, well-maintained engine is not the best use of your money. You might not need it if your vehicle gets regular oil changes every 5,000 miles and has no current symptoms like ticking, rough idle, oil burning, or poor compression. 

Experts generally suggest that if you are not experiencing problems, do not add anything extra. At most, some recommend it as a deep-cleaning cycle every 50,000 to 100,000 miles, not at every service interval.

The vehicles that can genuinely benefit are those with a neglected maintenance history, engines that have sat unused for long periods, or high-mileage engines where deposits have started affecting moving parts. 

Here’s one example we could online: a Toyota Tundra with over 270,000 miles on the clock. After a single 505CRO treatment, the oil went from honey-colored to black in about 20 minutes. That color change shows how much old deposit the product pulled off internal surfaces. Users in similar situations reported quieter engines, smoother idle, and in some cases, restored cylinder compression from previously stuck piston rings.

Many DIYers start by comparing engine additives to see if a simple solution will suffice, but for vehicles with severe carbon buildup, a professional-grade treatment like 505CRO could help.

Does 505CRO Actually Work?

The honest answer is: it depends, and opinions are split three ways.

Many users report clear improvements. Their engines ran quieter, idled better, and oil consumption dropped after the treatment. Some saw compression return in cylinders that had been low. These are mostly older, neglected engines where the product had real problems to solve.

Others saw no change at all. No improvement in performance, fuel economy, or noise. Some dismissed it as snake oil, arguing that consistent oil changes do more good than any additive.

The third group experienced problems after using it. A potent cleaner can dislodge large chunks of built-up sludge all at once. If that sludge travels to the oil pickup screen and clogs it, the engine can lose oil pressure. 

Some users also reported check engine lights, misfires, and fouled spark plugs or injectors shortly after treatment.

ATS Chemical recommends using 505CRO every other oil change to stay ahead of carbon accumulation. The broader mechanic and enthusiast community disagrees. Most experts say to use it only when you have a real problem to solve, not as a routine maintenance step. 

How to Use ATS 505CRO

Before you start, make sure you have everything you need: one 12oz bottle of 505CRO, a new oil filter, and enough fresh oil to refill your engine to the correct capacity. 

One bottle covers any engine size, whether it takes five quarts of oil or ten. Do not use more than one bottle per service. Adding more chemical does not improve results. Also make sure you are not mixing 505CRO with any other oil additives or treatments from other brands.

Step 1: Add the Treatment

With the engine off, remove the oil fill cap and pour the entire bottle into the crankcase. Replace the cap.

Step 2: Run the Cleaning Cycle

Start the engine and bring it to a high idle between 1,500 and 2,500 RPM. Do not drive the vehicle during this process. The treatment is designed to work at a steady idle only. Changing RPM while driving can interfere with the cleaning cycle. If you are at a shop, pour the treatment in the parking lot and move the vehicle only a short distance into the service bay once the cycle is finished.

How long you run the cycle depends on what you are trying to fix. For routine maintenance, idle the engine for 10 to 20 minutes. For more serious issues like stuck piston rings, extend the cycle to 40 to 45 minutes, and occasionally bring the RPM up to 2,500 to 3,000 for short bursts during that time.

Step 3: Drain Immediately

Once the cycle is complete, drain the engine oil and remove the old filter right away. The engine will be hot at this point. Some users recommend letting it cool briefly or using a fan before draining to avoid burns. To make sure all loosened deposits and chemical residue are fully removed, some owners pour two quarts of fresh oil through the crankcase while the drain plug is still out. This flushes out anything left behind.

Step 4: Refill

Install a new oil filter and refill the engine with fresh oil at the manufacturer-recommended weight for your vehicle.

A Word of Caution

If your engine has been neglected for a long time, be aware that 505CRO can dislodge large amounts of sludge at once. That sludge has to go somewhere, and if enough of it reaches the oil pickup screen, it can restrict oil flow to the engine. This is a real risk on heavily neglected engines and worth keeping in mind before you use the product.

505CRO vs. 505CRF: What’s the Difference?

505CRO and 505CRF clean different parts of the engine and go in through different openings.

505CRO goes into the crankcase, the same place you add engine oil. It targets the oil-lubricated side of the engine: piston rings, lifters, camshaft phasers, timing chain tensioners, and oil screens. 

505CRF goes directly into the fuel tank. It travels through the fuel system during normal operation and targets the combustion side of the engine: fuel injectors, induction ports, intake valves, and combustion chambers. Carbon buildup on injectors and valves is a common cause of rough idle, hesitation, and reduced fuel economy.

Alternatives to ATS 505CRO

BG Dynamic Engine Flush is the most commonly cited professional-grade alternative. It is part of a multi-step process that includes BG Dynamic, BG MOA, and a dedicated rinse oil. Shops typically charge around $300 for the full service. It is well-regarded in the professional mechanic community, but the cost is significantly higher than doing it yourself with a pour-in treatment.

Liqui Moly Motorspülung, also sold simply as Liqui Moly Engine Flush, is a more affordable option that comes up frequently in community discussions. Some Liqui Moly oils also contain molybdenum disulfide, which provides added lubrication during the cleaning process.

Motor Medic takes a different approach. Some users run the detergent version through a full oil change interval to gradually clean the engine, then follow up with a Motor Medic flush right before draining. It is a slower method but gentler on the system.

Closing Notes

505CRO is not a maintenance product, and it is not a substitute for proper engine care. It is a chemical cleaning treatment designed for engines that already have a problem. 

Modern engines make carbon buildup a more serious issue than it used to be. Low-tension piston rings and turbocharged systems run at tighter tolerances and higher heat, which means deposits that might have been a minor nuisance in older engines can cause real mechanical problems today. 

When those problems show up and a full engine teardown is not yet warranted, 505CRO offers a middle-ground option.That said, the “Professional Use Only” label on the packaging needs to be taken seriously. 

This is a potent solvent. Used on the wrong engine, or used incorrectly, it can do more harm than good. The risk of dislodging large amounts of sludge and clogging the oil pickup screen is real, and it is not a small problem if it happens.

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