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Ford 7.3 Power Stroke Aluminum Expansion Tank R&D Part 1 – Stock Review and Design Plans

When it comes to the icon of reliability, durability, and longevity in the automotive world, all eyes are on the diesel powertrain. The recognizable chugging sound of a diesel engine has become synonymous with the thought of tractor trailers, incredible fuel economy, and reaching 300,000 miles with ease. “Built Ford Tough” reigns true for all the general features of the diesel platform, the Powerstroke. Giving our loaner F-250 a look over, it’s easy to see why. Everything incorporated into the design was done so with the intent to develop an invincible machine. Everything except for the expansion tank, it seems.

Our spare stock tank gets a light coating in preparation for it's 3D scan.
Our spare stock tank gets a light coating in preparation for it’s 3D scan.

It goes without saying that the cooling system routed throughout the engine bay of your 7.3 Powerstroke works best when the coolant stays in it. In fact, that’s one of the main design requirements. Losing coolant pressure, or coolant in general, is already frustrating enough for anyone, but there’s no quicker way to bring a work day to a screeching halt or put a serious damper on hauling the camper to the overnight site than spewing coolant from the tank that was designed to hold it. By now, it’s no secret that the factory Ford expansion tank is a weak link in the cooling system chain. Specifically, defects are found at the seams where the different sections of the tank are molded together, and inlet from the radiator.

This barbed port is one of the weak points in the design. Constant heating and cooling cycles cause the connection point to become brittle, and crack even from accidentally leaning on it.
This barbed inlet port is one of the weak points in the design. Constant heating and cooling cycles cause the connection point to become brittle, and crack even from accidentally leaning on it.

The root of the issue lies within the construction of the tank itself. It is very common for manufacturers to utilize high-grade plastics such as polypropylene or high-density polyethylene in the construction of fluid tanks under the hood, and Ford is no exception. These plastics are generally tough, and are able to withstand the heat produced by the engine, and especially the heavy lifting that the 7.3 partakes in, but there’s always a downside to using the cheaper and lighter material. They’re just not as durable over the long term.

The extreme heat that is produced by the engine, especially while under heavy load, which is exactly what this truck was intended for, is an obvious suspect for the degradation of the tank’s plastic construction. The polypropylene that these tanks are made from has a relatively low melting point considering the 190-215°F operating temperature of the Powerstroke. While polypropylene doesn’t start to melt until upwards of around 350°F, the constant heat does gradually break down the material. The heat has two accomplices, the first being the cold. While the heat gradually breaks down the plastic walls, the cold, and especially below freezing temperatures, can cause brittleness in these kinds of plastics. On top of that, the pressure of hot gasses being released from the hot coolant are constantly pressing on the outer walls of the tank. Combine the heating and cooling cycles together, with the pressure from the gasses and it’s no wonder that these tanks need to be replaced often.

Our Faro Design ScanArm is becoming quite the celebrity lately. Steve scans our factory expansion tank, creating a 3D model and generally streamlining the design process.
Our Faro Design ScanArm is becoming quite the celebrity lately. Steve scans our factory expansion tank, creating a 3D model and generally streamlining the design process.
Steve wanted a closer look at the stock tank's internal structure, so he decided to break out the cutting wheel.
Steve wanted a closer look at the stock tank’s internal structure, so he decided to break out the cutting wheel.

We intend to correct these flimsy stock flaws with our new design. The first thing to go is the plastic. No, we didn’t work out some kind of fancy expansion tank delete, but we’re going to replace the ditched plastic with aluminum. The main shell will be extruded, and sides will be welded on to reduce the number of seams and make them exponentially stronger than those on the original design, amounting to the last expansion tank you’ll ever need to buy for your Ford truck.

These internal baffles are in place to keep the coolant level from shifting around in the tank while driving. Our new design will also incorporate a similar system.
These internal baffles are in place to keep the coolant level from shifting around in the tank while driving. Our new design will also incorporate a similar system.
While I know I just gave plastic a bad rap, it's still very useful in our prototyping process, and we can easily visualize, and test fit our designs.
While I know I just gave plastic a bad rap, it’s still very useful in our prototyping process, and we can easily visualize, and test fit our designs.

We aren’t going to just stop at making the tank more durable, either. Aluminum, while being more durable than the original plastic, isn’t translucent. Checking the fluid level can get a little tricky when you can’t see it, so we plan on adding a sight tube to ease the guesswork of determining how much is in the tank. We also know the importance of monitoring just about every temperature and pressure sensor in your heavy-duty towing machine, hence why we plan on adding in a bung, too, for connecting a gauge to check if coolant is flowing as it should.

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Our designs are in the process of going from drawing to production sample, and are due back at our facility in the coming weeks.

 

Thanks for Reading!

-Nick

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