Few parts of a diesel vehicle work harder while getting little attention than the diesel exhaust manifold. Diesel exhaust manifolds do the dirty work of collecting all the fumes issued by the engine before directing them toward the catalytic converter, which filters the exhaust. That’s the simplest definition, but there’s much more to it than that.

An exhaust manifold is an integral part of the exhaust system that sits right on top of the cylinder head. It takes exhaust gases collected from the individual cylinders to the turbocharger or to a collector pipe. These remarkable devices work tirelessly, keeping the exhaust gases moving along without interrupting the performance and flow of the engine. Before all that happens, diesel exhaust manifolds must gather the fumes without interfering with engine pressure. They’re the first step in a vehicle’s exhaust system.

Diesel exhaust manifolds feature tough materials that allow them to work under extreme temperatures and pressures as they transfer the exhaust through the exhaust pipe (or pipes, as the case may be). The diesel exhaust manifold is under more stress than the rest of your car. The forces at work on the manifold are immense, especially given its exposure to extreme heat from the exhaust gases (which can reach more than 1,000°C under heavy use).

All that said, not all diesel exhaust systems are the same. Read on to learn all about the different types of diesel exhaust manifolds.

Log Manifolds

Log manifolds are standard-issue diesel exhaust manifolds. Commonly found in many diesel engines, they’re also the simplest option. The name comes from their appearance, as these manifolds somewhat resemble metallic campfire logs. Built with a single interior chamber, they gather the exhaust gases inside before passing them through the rest of the system. The design is simple, making it less expensive and time-consuming to mass produce, and it allows the turbo to spool quickly. However, a classic log manifold creates back pressure, which can impede engine performance.

Tubular Manifolds

Now, we’re getting a little more complex, design-wise. Tubular manifolds may be better known by another name: headers. These designs improve on the classic log manifold by connecting each cylinder’s exhaust port to a separate tube. This layout allows exhaust gases to flow more freely and easily, abating that pesky back pressure engendered by the log manifold. The engine can “breathe” better, so to speak, which translates into better performance, more horsepower, extra torque, greater efficiency, and better use of fuel all around. Most of the time, you’ll see headers employed in higher performance vehicles or race cars. Tubular manifolds come in different shapes and configurations. You’ll find them in forms such as “shorty” and “long tube” headers.

Cast Iron

Manufacturers create exhaust manifolds using one of two metals: cast iron or stainless steel. But which is better? More precisely, which is better for which functions and jobs performed by diesel vehicles?

We’ll begin with cast iron. A diesel exhaust manifold has to be capable of facing extreme temperatures even under normal use and handle low temperatures as well. Temperature extremes can lead to an engine cracking, warping, or otherwise breaking apart or losing a gasket or other seal. Cast iron is a great candidate for withstanding these extremes.

Additionally, cast iron may make a tremendous clatter when you drop it on the ground, but if it’s part of an exhaust manifold, it keeps things nice and quiet under the hood. Overall, you should choose cast iron for reliability, low maintenance, and affordability.

Stainless Steel

To match its clean-sounding name, stainless steel proves great for manifolds because its non-porousness allows for easy cleaning. Stainless steel fights the corrosion that might afflict cast iron and looks snappier on a diesel engine. Stainless steel also resists moisture, specifically in humid environments. This material thrives in salty air, resisting the corroding effects of salinity in the environment as well. However, added resistance means that stainless steel diesel exhaust manifolds will cost a bit more. So, budget for it if you can.

When To Replace

Unless you’re choosing to replace your diesel exhaust manifold for performance reasons, the model on your vehicle is often the most reliable one. Whether you have a 2006 5.9 Cummins turbo back exhaust system or another kind, there are signs to watch and listen for when it’s time to replace a diesel exhaust.

Cracks and Fissures

When you first buy your truck, look under the hood to familiarize yourself with your vehicle. A brand-new engine should be clean and damage-free. Take time to check in and see if your manifold has cracks, fissures, or other signs of age.

Listen for the Tick

Vehicles should never tick like a clock. When you do hear a ticking sound under the hood, it could stem from a leak in the exhaust manifold. When it gets cold, an exhaust manifold will usually tick more loudly because the gases are seeping out and around the engine. When the temps rise, the tick may go away, but that’s not good either. The engine will suffer, and carbon monoxide may seep into the cabin.

Listen for Extra Roars

A good engine often has a satisfying roar, but sometimes, roaring can be a bad thing. If extra noises follow the usual roar, a crack may be forming in the engine.

Failed Emissions Test

Emissions tests should always be an easy “A” in a manner of speaking. If you fail an emissions test, have the car inspected. The issue could stem from a faulty exhaust manifold.

Bad Smells

If the smell of exhaust starts creeping into the cabin, immediately bring your vehicle to a mechanic. The manifold may be damaged, putting you at risk.

Low Fuel Efficiency

Not getting enough miles to the gallon? There could be several causes, but a noticeable drop in efficiency could stem from your exhaust manifold damage.

The Engine Light Comes on

When the engine light flickers on, it’s rarely good news. Take it in for an inspection right away.

We’ve explored the different types of diesel exhaust manifolds, as well as some of the pros and cons of the different types. If you have any questions, contact us for a consultation today!