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The Truth About Plastic Under Your Jeep’s Hood

The Truth About Plastic Under Your Jeep’s Hood

I Speak Jeep Mar 25, 2026 78 min
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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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Technical Too Afraid to Ask
Concept

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.

Concept

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.

Brand

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.

Company

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.

Company

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.

Term

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.

Term

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.

Part

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.

Term

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.

Part

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.

Term

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.

Part

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.

Concept

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.

Term

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.

Part

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.

Term

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.

Concept

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.

Concept

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.

Term

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.

Term

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.

Term

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.

Concept

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.

Term

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.

Term

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.

Term

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.

Term

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.

Term

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.

Concept

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.

Term

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.

Company

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.

Term

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.

Brand

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.

Concept

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.

Company

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.

Concept

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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