The Truth About Plastic Under Your Jeep’s Hood
About this episode
The crew celebrates episode 200 by tackling the “plastic under your Jeep’s hood” debate, tracing Jeep’s history of plastic failures from CJ-era valve covers and radiator tanks to TJ/JK cooling and modern oil coolers. They argue plastic isn’t automatically the enemy—often the real culprits are seals, over-tightening, service practices, and design revisions across years. A big focus is 2011–2024 oil cooler assemblies, why aluminum upgrades don’t always fix leaks, and how Mopar’s repeated seal redesigns matter more than material headlines. They also discuss plastic intake components, heat management, and connector wear.
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Modern Jeeps use more plastic under the hood than ever before—and a lot of people hate it. But is it actually a problem? In this episode, we break down why manufacturers use plastic components in the engine bay, what they’re designed to handle, and where they actually fail (if they do). Not all plastic is created equal, and not all of it is a weak point.
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Jeep
"In my oversized four-wheel drive Jeep A Jeep podcast starring industry experts"
Jeep is a car brand that makes vehicles built for off-roading. When people say “Jeep” in a podcast, they usually mean the brand’s 4x4 models and how their parts work.
Jeep is a U.S. automaker best known for rugged 4x4 vehicles and off-road capability. In enthusiast circles, “Jeep” often refers to both the brand and the specific platform/parts ecosystem used across models.
four-wheel drive
"In my oversized four-wheel drive Jeep A Jeep podcast starring industry experts"
Four-wheel drive powers all four wheels, which helps the car grip better when the road is slippery or uneven. It’s especially useful for off-roading.
Four-wheel drive (4x4) means power is sent to all four wheels, improving traction on loose surfaces like dirt, snow, and rocks. Many Jeep models use 4x4 systems designed for low-speed control and off-road climbing.
4x4
"In my oversized four-wheel drive Jeep A Jeep podcast starring industry experts"
“4x4” just means the vehicle can drive all four wheels. That helps it handle rough or slippery terrain better.
“4x4” is shorthand for four-wheel drive, emphasizing that traction is available at all four wheels. It’s commonly used in off-road communities to distinguish from two-wheel-drive vehicles.
Mishimoto
"Yes specifically Griffin and Mishimoto And I'll continue to shout that from the rooftops"
Mishimoto makes aftermarket cooling upgrades, like radiators. The hosts are talking about how the results didn’t match what they expected.
Mishimoto is a well-known aftermarket brand for cooling upgrades, including radiators, intercoolers, and coolant-related components. The episode’s framing suggests the hosts have strong opinions about what they were promised versus what they experienced with these cooling products.
Griffin
"Yes specifically Griffin and Mishimoto And I'll continue to shout that from the rooftops"
Griffin is a company that makes aftermarket cooling parts, like radiators. People choose brands like this when they want better cooling than the original equipment.
Griffin is an aftermarket cooling-parts brand best known for performance radiators and related cooling components. In enthusiast circles, people often compare Griffin’s radiator designs and fitment versus other brands when chasing better cooling or reliability.
fasteners
"First, A Second How many fasteners should a valve cover have On it Not two"
Fasteners are the bolts that hold the valve cover in place. If there aren’t enough of them, or they’re placed poorly, the cover can sit unevenly and cause leaks or damage.
Fasteners are the bolts/screws that hold components together. For a valve cover, the number and placement of fasteners matters because it controls how evenly clamping force is distributed—especially around areas that need reinforcement to prevent leaks or cracking.
interwebs
"[623.3s] It was the 80's [624.8s] You didn't have the interwebs [626.0s] And the supercomputers in your pocket"
“Interwebs” just means the internet. The speaker is saying that in the 1980s you couldn’t easily search for and order parts online.
“Interwebs” is a casual reference to the internet, used here to highlight how online parts lookup and ordering didn’t exist in the same way in the 1980s. That matters because sourcing discontinued or niche components (like certain plastic caps) could be extremely difficult.
Radiator
"I did have a Radiator I remember where I was The day mine exploded"
The radiator is part of the cooling system. It helps keep the engine from getting too hot by cooling the liquid that circulates through the engine.
The radiator is the heat exchanger that helps cool the engine by transferring heat from the coolant to airflow. If it fails or becomes clogged, the engine can overheat quickly, sometimes leading to dramatic steam events.
steam
"And I thought What in the heck was that And then steam started coming out of the hood"
If you see steam under the hood, it often means the cooling liquid is getting too hot and boiling. That usually points to a problem in the cooling system.
Steam coming out of the hood is a common sign of coolant boiling due to overheating, often from a cooling system leak or component failure. In this context, it follows the mention of a radiator, suggesting a cooling system failure event.
Cladding
"[792.5s] Cladding [795.6s] There's plenty in your life [798.0s] That is plastic that you don't think about"
Cladding is the protective trim on the outside of the vehicle. It’s often plastic and helps shield parts from dirt, rocks, and everyday wear.
Cladding refers to exterior trim panels—often plastic or composite—that cover and protect areas like wheel arches, lower body sections, or engine-bay components. It’s commonly used to reduce damage from road debris and to give the vehicle a finished look.
oil cooler
"[1007.0s] So anyways this is now [1008.5s] We get an oil cooler [1009.3s] If you didn't understand folks"
An oil cooler is like a little radiator for your engine oil. It helps keep the oil from getting too hot, which is important for engine protection.
An oil cooler is a heat exchanger that helps remove heat from engine oil (often by routing oil through a small radiator-like unit). Keeping oil temperatures under control helps protect oil viscosity and can extend engine component life, especially under towing or off-road stress.
valve covers
"[1034.0s] Because as you have already outlined [1036.5s] We have valve covers [1037.3s] And we do have upper manifolds"
Valve covers are the covers on top of the engine that help keep oil from leaking out. They also protect the parts under them and use a gasket to seal properly.
Valve covers are the housings that sit on top of the engine’s cylinder head(s) and protect the valve train area. They also help keep oil contained and often seal with gaskets to prevent leaks.
cold air intakes
"[1047.8s] And I want to talk about [1049.1s] For a brief moment I want a side quest [1052.3s] Into [1053.6s] Cold air intakes and or just [1056.0s] Your air intake"
A cold air intake is a system that tries to bring in cooler air from outside the engine bay. Cooler air can help the engine run better, but it depends on the exact kit and how it’s set up.
Cold air intakes are aftermarket (or sometimes OEM) intake systems designed to pull cooler outside air into the engine. Cooler, denser air can improve combustion and sometimes power, but results depend heavily on the specific setup and tuning.
heat transfer
"With metal tubes Which is awesome for heat Transfer Metal transfers and Holds heat"
Heat transfer is how heat moves around. With intake parts, it matters because hotter intake air can reduce engine efficiency.
Heat transfer is the movement of heat from one material to another. In intake systems, the material and routing of the intake piping can influence how much heat the incoming air picks up under-hood.
throttle body
"Rubberish plastic to Going to the throttle body So we're talking"
The throttle body is basically the engine’s “air gate.” It controls how much air gets into the engine, and the parts leading up to it affect how well the engine breathes.
The throttle body controls how much air enters the engine by regulating the throttle plate opening. Intake components like the air box and ducting are designed to deliver air to the throttle body consistently, and heat management matters because hotter air can reduce engine efficiency.
thermal conducting properties
"It has different Thermal conducting properties than metal does A thin aluminum tube Will allow heat transfer"
This is about how easily a material lets heat pass through it. Metal usually moves heat more easily than plastic, so the engine bay can heat them differently.
Thermal conductivity is a material’s ability to transfer heat. Metal generally conducts heat more readily than many plastics, so the same under-hood temperature can affect metal and plastic intake parts differently—either transferring heat faster or isolating it more.
Engines are air pumps
"Engines are air pumps and they want cold dense Air"
An engine’s job is to pull in air, mix it with fuel, and burn it to make power. Cooler, denser air usually helps the engine make better power.
Most internal-combustion engines work by moving air (and fuel) into cylinders to create power. The amount and temperature of intake air affect how efficiently the engine can burn fuel.
R&D
"You know r&d some Stuff and We we designed Oil cooler goes down in the bellies"
R&D means research and development—basically the work engineers do to design and test new ideas. Here, it’s explaining that the change wasn’t random; it was engineered.
R&D (research and development) is the process of designing and testing new engineering solutions before they reach production. In this context, it frames the oil cooler design as something the manufacturer developed through testing and iteration.
push rods
"They like their push rods They like their their old School"
Pushrods are parts inside the engine that help open and close the valves. Some people prefer older engines that use pushrods because they’re familiar and often simpler.
Pushrods are part of a traditional valvetrain design that transmit motion from the camshaft to the engine’s valves. When people say they “like their push rods,” they’re usually referring to the feel, sound, or perceived simplicity of that older-style setup.
crank windows
"I have a truck with the crank windows And I don't like that Anyway It's going to convert all this crank windows To electric even on the old school"
Crank windows are windows you open and close by turning a handle by hand. Power windows use a button and a motor instead.
Crank windows are manual side windows operated by a hand crank instead of a power switch. They’re common on older or more basic truck trims because they don’t require electric window motors.
oil filter
"About the doorman oil filter [1813.7s] But Mishimoto in my opinion"
The oil filter cleans the oil that circulates through your engine. If the filter isn’t right for your Jeep, it can affect how well the engine stays protected.
An oil filter removes contaminants from engine oil so the engine can stay lubricated and protected. Filter design and part-number revisions matter because they can change flow characteristics, filtration media, and compatibility with specific engines.
reverse engineering
"[1943.5s] Yes and the minute you [1945.0s] Take your blueprints over and you hand them [1947.5s] To a Chinese manufacturing plant [1949.8s] They are copying"
Reverse engineering means copying something by taking it apart and figuring out how it works. With car parts, that can be risky because the copy might not be made as well as the original.
Reverse engineering is when someone studies an existing product (or its design) and recreates it without the original maker’s permission. In automotive parts, it often leads to copies that may match the look but not the materials, tolerances, or durability.
molecules of the plastic
"Because a chemical process happens Which basically changes the Molecules of the plastic Then you have one"
Plastics are made of long chains of molecules. Heating can change how those chains are connected, which is why the plastic can become more heat-resistant—or start to break down if it gets too hot.
This refers to the chemical structure changing during curing or overheating. When polymers undergo a chemical process, their molecular bonds rearrange, which can make the material more heat-resistant (or, if overheated, cause it to degrade).
chemical process happens
"Because a chemical process happens Which basically changes the Molecules of the plastic Then you have one"
The speaker is saying the plastic isn’t just heated—it actually changes chemically. That’s what makes it act more “permanent” after it’s set.
The speaker attributes heat stability to a chemical reaction occurring during curing. That reaction alters the polymer’s structure so it behaves differently under heat than a plastic that simply softens and melts.
head gasket
"Where I think we had a head gasket ... Not plastic, it's actually A steel head gasket with aluminum Block and head basically"
The head gasket is like a seal between the engine block and the top part of the engine. If it breaks, fluids can leak or mix, and the engine can start running hot.
A head gasket seals the connection between the engine block and the cylinder head. If it fails, coolant and oil can mix or leak, which can lead to overheating and other drivability issues.
Polyethylene Tertone
"[2487.1s] Polyethylene [2488.8s] Tertone [2490.0s] Or that [2492.1s] Is also known as"
This is the name of a type of heat-resistant plastic. The exact name in the transcript is a bit unclear, but the point is that different plastics handle engine heat differently.
The transcript appears to be referring to a specific high-temperature polymer used in under-hood parts. “Polyethylene Tertone” is likely a mis-transcription of a known engineering plastic name (commonly “polyetherimide” or “PTE/PET” family terms), so listeners may benefit from clarifying the exact polymer being discussed.
carbon fiber
"And they can also add carbon fiber To that, so then you basically have a race car I hear race car"
Carbon fiber is a strong, lightweight material made from tiny carbon strands. Race cars use it because it helps the car feel more rigid without adding a lot of weight.
Carbon fiber is a lightweight, high-strength composite material made from carbon strands woven into a fabric and bonded with resin. It’s commonly used in motorsports and performance vehicles to reduce weight while improving stiffness and strength.
cleaning out an artery
"[2650.3s] Because they are kind of thin [2652.2s] They're tight. It's like cleaning out an artery [2654.1s] At that point in time."
They’re using a health analogy: if a passage is “clogged,” flow gets restricted. In an engine, carbon buildup can similarly block or restrict small channels.
The “cleaning out an artery” analogy compares removing deposits from narrow passages to restoring blood flow in a clogged vessel. In engines, thin/tight passages can accumulate carbon or buildup, restricting flow and contributing to drivability issues.
Derometer difference
"And we're talking about Derometer difference We're talking about slight profile difference They're trying to"
This sounds like they’re talking about the seal material’s firmness. A slightly different firmness or shape can help the seal fit better and stay sealed longer.
“Derometer difference” appears to refer to a material hardness or durometer difference—how stiff or flexible the seal material is. Changing durometer/profile can improve how the seal conforms under pressure and heat, reducing leak risk.
Felpro
"That [2905.4s] The sealing plastics [2908.8s] That we see through Felpro [2911.2s] And Molly"
Fel-Pro is a company that makes replacement gaskets and seals for cars. The host is saying you’ll often see their sealing materials on Jeep-related repairs.
Fel-Pro is a well-known aftermarket gasket and seal brand. In the context of this episode, they’re being referenced as a source of “sealing plastics”/sealing materials used under a Jeep’s hood.
all-aluminum cooler
"But I like that all-aluminum cooler They will Factually Sell you an all-aluminum Oil cooler"
An all-aluminum oil cooler is made mostly from aluminum. Aluminum can move heat away from the oil efficiently, which helps the engine run at safer temperatures.
An all-aluminum oil cooler uses aluminum for the heat-exchange surfaces, which can improve heat transfer and corrosion resistance compared with some other materials. In practice, the big differentiator is often fitment and the specific design used by the manufacturer.
Mopar
"It will be an authorized Mopar accessory That is what it will be listed as"
Mopar is the official parts brand for Chrysler/Jeep (Stellantis). If something is a Mopar accessory, it’s usually made to fit your Jeep correctly.
Mopar is the Chrysler/Stellantis umbrella brand for OEM parts, accessories, and service products. When a part is listed as a Mopar accessory, it generally means it’s an official catalog item intended for correct fitment and compatibility.
re-box
"[3464.3s] By doorman [3465.3s] It is a re-box [3466.9s] They put it in a Mopar box"
“Re-box” means the part is made elsewhere, but it gets put into a different brand’s box. So the label changes, but the actual product might be the same.
“Re-box” here means the same underlying product is packaged under a different brand label. The speaker’s point is that the hardware may not be uniquely “OEM-designed,” even if it’s sold through the OEM (Mopar) channel.
AutoZone
"[3505.6s] It's a couple bucks more than if you were to just go on to Amazon [3507.9s] And buy the doorman yourself or go to AutoZone [3509.7s] And buy it yourself"
AutoZone is a store where you can buy car parts without going through a dealership. The point here is that you can often buy the same kind of part yourself.
AutoZone is a major aftermarket auto-parts retailer in the U.S. The episode contrasts buying a part from a dealer versus buying it yourself from a chain like AutoZone.
plastic is not inherently bad
"[3528.2s] The takeaway here [3530.7s] The takeaway is that plastic is not inherently bad [3534.1s] It's here to stay"
This is the episode’s main argument: plastic components in the engine bay aren’t automatically inferior to metal. The speaker frames plastic as a normal, long-term design choice rather than a temporary compromise.
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