Dorman Products FAQ: LS Oil Cooler Block Off Plate, 3 Inch Intercooler, Semi Truck Exhaust Pipe, and Oxygen Sensors

The questions that come up when a truck is on the lift

I work at an automotive parts distributor, and a large part of my job is triaging rush orders. A shop calls in, they've got a truck on the lift, the customer is standing there, and the part that was supposed to show up this morning didn't. In my role, I'm the one who figures out what to do in the next hour, not the next week.

After about 12 years and more than 300 rush orders, I've noticed the product questions are always pretty consistent. My focus is always the same: how much time do we have, can we get the right part in that window, and what's the worst case if we're wrong. Here are the six questions I get most often, answered the way I would if you'd called in right now.

What is Dorman Products, and does the Dorman Products logo tell you anything?

Dorman has been around since 1918, but honestly, most people still don't fully understand what they do. They're not a traditional aftermarket brand that just copies an OEM part and sells it cheaper. Dorman looks for problem parts — components that fail regularly on factory vehicles — and then engineers a corrected version. That's why their catalog is so broad: door handles, power steering lines, and yes, engine components like the LS oil cooler block off plate we'll get to next.

The logo itself is simple: red background with "DORMAN" in white. Newer packaging also includes a stylized brand mark. The more practical thing to know is how to spot a counterfeit. Genuine Dorman boxes have crisp, clean print and a part number that matches their online catalog. The part will usually have "DORMAN" molded into the plastic or stamped into the metal. If you're looking at a product with a blurry label or no branding at all, that's a red flag — knockoffs exist, especially on marketplace sites.

That said, the logo isn't what makes the part work. It matters less than verifying that the part number is correct for your application. We've had customers show up with a "Dorman" part that wasn't actually Dorman at all — just a repackaged no-name component. It failed fast, and gave the real brand a bad name.

Is the Dorman LS oil cooler block off plate the right choice?

This comes up constantly with LS swaps and engine bay cleanups. The factory oil cooler sits under the oil filter adapter, and when you delete it — for clearance or to simplify the system — you need a block off plate to seal those oil passages. If it leaks, you lose oil pressure, and you can lose the engine.

"Any block off plate works; it's just a flat piece of metal with a gasket." That's what the forums say. In practice, it's not that simple.

We've seen cheap plates warp during torque-up, and we've seen gaskets cut wrong. The Dorman version is machined flat, and it's designed to maintain proper oil flow to the filter and the engine. We stock it for a reason.

I only fully believed the difference after I skipped the brand-name option once to save a few dollars. That was a mistake. The cheap plate didn't seal properly, and the truck was back in the shop within a week. Saved $8, spent $150 in labor to make it right. I don't make that call anymore.

Practical tip: don't assume the plate comes with bolts. The Dorman kit does, but some listings don't. And check whether your specific LS block uses the older or newer oil filter adapter — the sealing surfaces aren't always the same.

What does a 3 inch intercooler actually do for a diesel truck?

Let's start with what "3-inch" means, because it varies between kits. On most diesel trucks, it refers to the diameter of the piping, but in some cases it's the thickness of the core. Either way, the goal is the same: more airflow and lower intake temperatures. A larger core gives the air more time to shed heat, and larger piping reduces restriction.

The theory is sound. Cooler air is denser, so you get more oxygen in each cylinder, which means you can burn more fuel and make more power. In practice — and I've seen a fair number of these installed — the gains on a basically stock truck are modest. If you haven't tuned the truck or increased boost, the stock intercooler is usually not the bottleneck. A 3 inch intercooler makes the most sense when it's part of a bigger system: tune, intake, and exhaust together.

Here's where my uncertainty kicks in: I genuinely don't know why some kits fit cleanly and others turn into a weekend project. My best guess is it comes down to the core dimensions and end tank design — two specs that aren't always clearly listed in the product description. I've been burned by assuming. I ordered a "3-inch kit" once, confident the piping would match the existing charge pipes. It didn't. The outlet was 2.5 inches and the charge pipe was 3 inches. That was a 4:30 PM Friday discovery, which is the worst time to find out you're missing an adapter.

So before you order: measure your existing setup, confirm the inlet and outlet sizes, and buy a kit that includes the right clamps and couplers. If the listing doesn't show dimensions, ask.

How do you choose a semi truck exhaust pipe that won't annoy you later?

Exhaust pipe for heavier trucks is a different world than light-duty. The temperatures are higher, the vibration is constant, and in many areas, inspections are more serious. The two big decisions are material and diameter.

Aluminized steel is the budget option. It handles heat fine and looks decent for a while, but in a salt-belt state, it will eventually rust. Stainless steel costs more upfront, but it's basically a no-brainer if you're keeping the truck — the price difference is a lot smaller than the cost of replacing a corroded system later.

As for diameter, this is where people get carried away. A 5-inch or 6-inch exhaust on a mostly stock engine won't add power; it's more about sound and appearance. At best, a big pipe helps if you've upgraded the turbo or injectors. At worst, it can hurt low-end response because you're dropping exhaust velocity. The factory diameter is more or less the right baseline for a stock truck.

I'd be careful here, though — my direct experience is mostly light and medium duty. I can't speak as confidently to long-haul Class 8 setups. But across everything I've seen, the most common point of failure is the mounting, not the pipe itself. A system that doesn't hang correctly will develop rattles, stress the turbo connection, and eventually crack at the joints. Buy a kit with proper hangers and clamps, or budget for a fabricator's time.

And check your local regulations before you modify a commercial vehicle. The EPA enforces noise and emissions standards on heavy trucks, and some states will fail a truck for something as simple as an exhaust tip that exits in the wrong direction.

How does an oxygen sensor work, and why does brand matter?

An oxygen sensor — usually called an O2 sensor — measures the oxygen concentration in the exhaust stream compared to the outside air. The classic design uses a zirconia element that acts like a tiny battery. When oxygen levels on the two sides of the element differ, it generates a voltage. Rich mixture means less oxygen in the exhaust, which produces a higher voltage, generally around 0.8 to 0.9 volts. Lean mixture means more oxygen, which drops the voltage to around 0.1 to 0.2 volts.

The engine computer reads that signal and adjusts fuel delivery in real time. It's a closed loop: the sensor tells the ECM how the last combustion event went, and the ECM adjusts the next one. If the sensor drifts, gets slow, or fails outright, the computer starts guessing — and that's when you see poor fuel economy, a check engine light, or a failed emissions test.

One of the most common mistakes I see is replacing the wrong sensor. Upstream sensors (before the catalytic converter) handle fuel trim. Downstream sensors (after the cat) are there to monitor converter efficiency. They perform different jobs and aren't interchangeable, even when they look similar.

In March 2024, a shop called at 2 PM needing an upstream O2 sensor for a truck that was due for an emissions test the next morning. We had one in a warehouse across town, and a courier delivered it by 5:30. The technician got it installed that evening, and the truck passed inspection. If we hadn't had the right sensor, the shop would've had to reschedule the test and eat a day of downtime. That experience reinforced something for me: with sensors, having the right part matters more than almost anything else.

It's also why I'm wary of the ultra-cheap no-name sensors. I'll be honest — I tried one once. It failed within a year, and the diagnosis cost more than a quality sensor would've been in the first place. These days, I don't play that game. Brand-name OE-style sensors, whether genuine or from a reputable aftermarket brand like Dorman, are worth the difference.

There's a part of O2 sensor operation I still don't fully understand, and I'll admit it: how wideband sensors on newer trucks keep their accuracy across such a wide range of exhaust flow. The sensor uses a pumping current to hold a constant reference voltage, but the way that translates to an air/fuel ratio reading on a scan tool... I'd love someone to explain that at a level a parts guy can follow. In the meantime, I just need to know what vehicle it goes on and which plug it has.

The bottom line

The parts industry has changed a lot in the last decade. It's no longer a simple "OEM or cheap" choice. Brands like Dorman invest in engineering and solve real problems — that's a genuinely different landscape than it was even five years ago. But the fundamentals haven't changed: verify your application, check the fitment, and don't cut corners on parts where a failure means a truck sitting dead on a lift.

If you've got a question about a specific setup, ask when you call. Chances are good we've already seen the failure you're trying to avoid.