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Going the Distance – Aluminum Degas Tank, Part 1: Stock Review

Few activities in the automotive world are less fun than trying to gauge the fluid level inside an aging coolant tank. Like cleaning a bathroom drain, it’s a not-so-subtle reminder that no matter how clean you keep the outside, there’s something nasty happening inside. In the case of the 6.4L Powerstroke engine, the cast iron block and porous plastic tank mean that a grungy brown blob inhabiting your engine bay is inevitable. Oxides and other contaminates will eventually enter the coolant and be spread across the inside of the degas tank.

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Considering even the newest 6.4L is eight years old, cracking and leaks may soon become more pressing issues than just being ugly. We’ve learned from other vehicles that plastic is a cost-effective and acceptable material for most components in the engine bay; but when it comes to degas and expansion tanks, it can’t quite stand up to the long haul.

Fortunately, Mishimoto is here to help your engine bay look better and go the distance, leak free.

Those of you who frequent the Powerstroke forums have probably seen us talk about making a 6.4L degas tank for quite some time and are familiar with some of the challenges we will be facing along the way. But, for those of you who aren’t in the know, we’ll start at the beginning: the stock tank.

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The stock 6.4L Powerstroke Degas tank shares many features with other Ford coolant tanks that we’ve worked on recently. Like our 2015+ F-150 tank, the interior is filled with baffles to keep coolant from sloshing around and aerating. It has a lower hose with a quick-disconnect fitting and a few other standard hose-barbs, the usual suspects. Unlike many degas tanks, however, the 6.4L Powerstroke degas tank has a conjoined sibling. Molded into the plastic of the degas tank and extending towards the front of the truck is a very large, very plastic, battery tray.

We’ve seen something like this before. The 2011-2014 F-150 expansion tank is molded as one piece with the engine’s airbox. But the battery tray isn’t where the 6.4L part-inception ends. Underneath the battery tray is an odd-looking chamber with several hose barbs. Through some careful internet and part diagram sleuthing, our engineers were able to determine that the chamber is used as a vacuum reservoir for the four-wheel-drive system.

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All those components molded together meant that making a degas tank by itself would take some clever design. If you’ve seen our 2011-2014 F-150 expansion tank, you might know where we’re headed with this. For those of you that haven’t, I’ll leave the rest for next time.

Thanks for reading,
-Steve

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