Cast aluminum vs. plastic or stamped steel pans and covers

In this segment, we are focusing on upgrade options to the long-lived trend for auto manufactures to use stamped steel for differential covers, oil pans, and transmission pans, and fairly recently, using molded plastic for oil and trans pans. These materials certainly do a “good enough” job holding fluid in but are sub-par when it comes to heat dissipation and frankly, providing any other benefits.

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Setting the record straight

To clarify, the frequently used euphemism “tin” or sheet metal when describing the stamped steel material used is incorrect; tin is almost never used by itself but rather is alloyed for a particular purpose. For instance, a grocery aisle tin can is a tin-coated steel container. Oil pans are not made of tin but may be alloyed with tin and steel. Sheet metal is simply metal formed into thin, flat pieces. There are many different metals that can be combined to create sheet metal, such as aluminum, brass, copper, steel, nickel, and titanium.

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Plastic pans: a discarded reality

A somewhat disturbing reality of plastic being used for oil and trans pans is that they are discarded as part of the service cycle, only to require the customer to repurchase the exact same (underperforming) pan that was discarded (or hopefully recycled). It’s worth noting that plastic pans have been reported to warp, melt and the brittle plastic may fracture upon impact.  Molded plastic also acts as an insulator, holding in damaging heat.

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Quality and performance cost more

When it comes to the manufacture of aluminum pans and covers, the process of casting aluminum alloy is not cheap so your replacement part will certainly cost a lot more. However, cast aluminum alloy is much better at heat dissipation than stamped steel or plastic. Aluminum alloy conducts heat at least 3 times better than mild steel. So, all things being equal, a transmission with an aluminum pan will cool the fluid (depending on the environment) 3 times faster than one with a stock steel pan. At the time of publication, no heat dissipation data was available regarding plastic versus cast aluminum.

Adding to the cooling benefits of cast aluminum are fins (raised surfaces) on the outside that act to increase surface area and capitalize on the under-vehicle airflow that helps scrub away heat. Additionally, many pans and covers have internal heat sinks which radiate heat outward and act as baffles to reduce the oil sloshing effect. This ensures the oil stays available at the oil pickup and generally eliminates the possibility of oil starvation in hard cornering and heavy acceleration. Some aluminum pans and covers are engineered with cast gussets on the outer surfaces that add strength and provide rigidity to housings. This is an added benefit not afforded with stock stamped steel or some plastic versions.

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More is better

Many aftermarket pans and covers offer increased fluid volume over stock. Higher fluid volumes have the ability to suspend more particles for greater protection and extended service intervals. This fluid increase also contributes to keep temperatures lower because higher fluid volumes take longer to heat up. A nominal increase or decrease of 10 degrees is actually significant when considering heat’s detrimental effect on fluid, seals, and valve body components.

Other systems that contribute to lowering fluid temperatures are inline trans fluid and inline oil coolers which further increase fluid volume and take advantage of free-flowing air to cool fluid. Factory tube and fin components can be upgraded to the superior “bar and plate” style aftermarket coolers for even better cooling performance.

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Fluid can’t be too clean

Drainage is another benefit to upgrading to cast products. Many stock pans and covers now come without a drain plug. This creates the potential for unpleasant fluid showers when servicing. Even the stock ones that come equipped with a drain plug, the plug is sometimes located above the bottom of the pan, leaving a small pool of heavy, dirty fluid. That manufacturing decision ensures your fresh fluid becomes immediately contaminated with gritty sludge on each service interval. Of the stock pans that do come with plugs, many don’t have an integrated magnet so the abrasive metal grit continues to circulate, potentially causing havoc. Of course, the hope is all particles get lodged in the filter, but in my experience, even the best filters don’t catch everything. The better cast pans come with magnet-equipped drain plugs to catch and hold ferrous metals. The best plugs have integrated rare-earth neodymium magnets which are almost magnetic overkill, but your fluid can’t be too clean, so plugs with neodymium magnets included are worth seeking out.

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A lifetime of service

Durability is another consideration. Cast aluminum alloy is stronger than stamped steel or the plastic versions (obviously). If either of these factory parts has any substantial contact on a hard surface on-road, or off-road on a rock or being pierced by heavy brush is a quick way to end your fun and is potentially dangerous in remote locations. The cast options can last a lifetime and some manufacturers back up their products with a limited lifetime warranty to the first owner.

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Opting to stay stock

The stock pans and covers that current vehicles come with these days do an okay job and cost the consumer nothing extra (except those plastic pans I mentioned). The stock ones are lighter weight if that’s important to you. Some people comment cast aluminum is brittle, although that has not been my experience. There are some who believe cast aluminum is too porous, this also has not been my experience with higher-quality cast aluminum products. For those who feel this needs to be addressed, it has been noted on some forums that POR 15 can create a barrier, however, this decreases cooling properties.

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In summation

Depending on how hard you drive, tow, or race, one constant remains: seals, rings, and sensitive valve body components do not perform well at high temperature – especially for longer periods of time. In these conditions, the reality of greater wear and reduced service life is inevitable. Adding easily bolted-on aftermarket products that increase cooling, add rigidity, more fluid, and easier servicing to these high-heat-generating components makes the decision to upgrade one that each consumer should consider.

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