---
title: "CL-4 and FB-4 Oil: What API PC-12 Means for Fleets"
description: API finalized PC-12 as CL-4 and FB-4. Learn which oil your trucks need, key 2026 to 2027 dates, and how fleets should prepare for the switch to new oils.
image: https://info.kellerheartt.com/hubfs/trucking-highway-drive.jpg
---

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# CL-4 and FB-4 Are Official: What API's Finalized PC-12 Category Means for Your Fleet

[Brian McGrath](https://info.kellerheartt.com/blogs/author/brian-mcgrath)

 Nov 13, 2026

---

PC-12 is official. In March 2026, API approved the new heavy-duty diesel oil standard and split it into two categories:

- **API CL-4** replaces CK-4. It works in the engines you run today.
- **API FB-4** replaces FA-4. It's for newer engines built for thinner oil.

Licensed oils arrive January 1, 2027. That gives fleets about a year to get ready.

Below, we cover what changed, which oil your trucks will need, and what to do now.

New to PC-12? Start with our[PC-12 engine oil explainer](https://info.kellerheartt.com/blogs/what-is-pc-12-engine-oil).

## Key Takeaways:

- PC-12 is now two categories: CL-4 and FB-4.
- CL-4 replaces CK-4 and works in older engines.
- FB-4 replaces FA-4 and is only for approved engines.
- Licensing starts January 1, 2027.
- The biggest risk is putting the wrong oil in the wrong truck.

## What Changed When API Finalized PC-12?

[PC-12](https://rotella.shell.com/en_us/info-hub/diesel-oil-specs-tech-standards/pc-12.html) is no longer a proposal. It now has official names, official labels, and a start date.

- **New names**: The draft names PC-12a and PC-12b are now CL-4 and FB-4.
- **New labels**: API released the CL-4 and FB-4 "donut" symbols.
- **A start date**: Licensing begins January 1, 2027.

| What's the API donut? It's the round symbol on an oil container. It shows which API category the oil is licensed for. Only licensed oils can carry it. |
| --- |

Why the change? Engines built for 2027 emissions rules need more from their oil. CK-4 and FA-4 date back to 2016. The new oils hold up better under heat, reduce wear, and do a better job protecting aftertreatment systems like DPFs and SCR catalysts.

In short: API's PC-12 standard is final, and it replaces CK-4 and FA-4 with two new categories, CL-4 and FB-4. Licensed products can carry the new donut starting January 1, 2027.

For the full backstory, see our[original PC-12 explainer](https://info.kellerheartt.com/blogs/what-is-pc-12-engine-oil).

## What's the Difference Between CL-4 and FB-4 Oil?

CL-4 is the everyday oil. FB-4 is the specialist.

CL-4 works in current and older diesel engines, just like CK-4 does today. FB-4 allows thinner grades for better fuel economy, but only in engines the manufacturer approves.

| CL-4 vs. FB-4 |  |  |
| --- | --- | --- |
| Feature | API CL-4 | API FB-4 |
| Replaces | CK-4 | FA-4 |
| Works in older engines? | Yes | No, not universally |
| Viscosity | Standard grades (like 15W-40) | Thinner, down to xW-20 |
| Best for | Most trucks in a mixed fleet | Newer engines approved for it |

 

| "CL-4 will become the default successor for broad compatibility…. FB-4 will primarily affect engines designed for it." - Bill O'Ryan, API, [Fleet Equipment Q&A](https://www.fleetequipmentmag.com/api-pc-12-engine-oil-2027/) |
| --- |

Both new oils improve on the old ones in four areas:

- Better heat resistance
- Better wear protection
- Better compatibility with modern seals
- Better protection for aftertreatment systems

| Our Take: Most mixed fleets will run CL-4 in nearly every truck. FB-4 makes sense where the OEM approves it, and the fuel savings add up. Just don't put it in a shared bulk tank. |
| --- |

## When Will CL-4 and FB-4 Engine Oils Be Available?

Licensed CL-4 and FB-4 oils start shipping on or after January 1, 2027. According to[Fleet Maintenance](https://www.fleetmaintenance.com/equipment/emissions-and-efficiency/article/55370048/api-announces-availability-of-cl-4-and-fb-4), API opened its licensee portal on June 1, 2026, so oil brands could get products approved early.

 

| API PC-12 Rollout Timeline |  |  |
| --- | --- | --- |
| Date | Milestone | What Fleets Should Do |
| March 2026 | API approves PC-12 | Learn the CL-4 vs. FB-4 split |
| June 1, 2026 | Licensee portal opens | Ask your supplier about product plans |
| Late 2026 | OEMs share recommendations | Check manuals and dealer bulletins |
| January 1, 2027 | First licenses | Look for the new donut |
| Through 2027 | CK-4 and FA-4 sell through | Plan to stock both for a while |

Will CK-4 disappear overnight? No. It'll stay on shelves until existing stock runs out.

## How Should Fleets Prepare for API PC-12?

Plan now. Switch later. The biggest risks are on the shop floor, like the wrong oil in the wrong truck or a mislabeled bulk tank.

Here's a five-step plan for the next 6 to 12 months.

### 1. Sort Your Trucks

List every unit by engine and model year. Most will land in the CL-4 column. Any truck running FA-4 today is an FB-4 candidate. Buying 2027 trucks? Ask the dealer which oil the engine is approved for.

### 2. Look for the Donut

"PC-12 ready" on a label isn't the same as a license. Look for the CL-4 or FB-4 donut, and check it against your OEM's approved list.

### 3. Prevent Mix-Ups

This is where fleets lose money. Before the first CL-4 drum arrives:

- Label bulk tanks and hose reels by oil type
- Set a top-off rule for every truck
- Walk your techs through the CL-4 vs. FB-4 difference
- Keep FB-4 out of shared tanks

### 4. Reset Oil Analysis

New oil means new baseline numbers. Sample before you switch, then again after the first new-oil interval.

### 5. Plan Inventory Early

Don't overbuy CK-4 heading into 2027. Buy what you'll use near term, then phase in CL-4 as it ships. If you buy in bulk, talk to your supplier now.

 

| Our Take: We've seen category changes before, including the CK-4 rollout in 2016. Fleets rarely struggle because they ordered the wrong oil. They struggle because the shop floor didn't know what changed. A short training session goes a long way. |
| --- |

Not sure which trucks need CL-4 and which need FB-4?[Talk with our team](https://www.kellerheartt.com/pages/contact-us), and we'll help you build a plan.

## How Is Keller-Heartt Getting Ready?

We plan to stock licensed CL-4 and FB-4 oils as they hit the market. That way you won't have to hunt for product.

As a [Shell Prestige Licensed Distributor](https://info.kellerheartt.com/shell-tellus-hydraulic-oils-comparison-chart), we'll carry Shell Rotella CL-4 and FB-4 products. We'll also add TRUEGARD heavy-duty diesel oils as cost-effective options become available.

Here's how we help fleets:

- **Stock on hand** in our Chicago and Wisconsin warehouses
- **Bulk pricing** when you call in larger orders
- **Emergency bulk delivery** through KHEDS
- **Straight answers** on which oil fits which engine

Until then, browse our[commercial truck supplies](https://www.kellerheartt.com/collections/commercial-truck-supplies) for the oils and DEF your fleet runs on today.

## Plan Now for CL-4 and FB-4

PC-12 is final. CL-4 replaces CK-4 for most trucks. FB-4 replaces FA-4 in approved engines. Licensed oils arrive January 1, 2027.

Sort your trucks, look for the donut, label your tanks, and plan inventory early. Need help?[Reach out to our team](https://www.kellerheartt.com/pages/contact-us).

## Frequently Asked Questions About CL-4, FB-4, and API PC-12

### Is CL-4 oil backward compatible with CK-4 engines?

Yes. CL-4 is built to replace CK-4 and works in current and older diesel engines. It's expected to become the default oil for most mixed fleets. Always double-check your OEM's maintenance manual before switching.

### Can I use FB-4 oil in older trucks?

Usually not. Like FA-4, FB-4 isn't universally backward compatible. It allows thinner grades that only certain newer engines are designed for. Use it only when your engine maker approves it.

### When can I buy CL-4 engine oil?

Licensed CL-4 and FB-4 oils can carry the API donut starting January 1, 2027. Expect products to roll out in early 2027, with wider availability as CK-4 stock sells through.

### Does PC-12 replace CK-4 and FA-4?

Yes. PC-12 was the development name for the new standard. CL-4 replaces CK-4, and FB-4 replaces FA-4. The older oils will phase out gradually after licensing begins.

### Can I mix CK-4 and CL-4 oil?

CL-4 is designed to be backward compatible with CK-4, so topping off should be fine. Check your OEM's guidance first. Avoid mixing either one with FB-4 or FA-4, and log any top-offs for oil analysis.

### What is the API donut on engine oil?

The API donut is the round symbol on licensed engine oil containers. It shows the oil's API category, like CL-4 or FB-4, and its viscosity grade. It's the quickest way to confirm an oil meets the spec.

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