GM Duramax coolant expansion bottle.

A coolant bottle that won't burn you if you remove a hot cap!

GM came to my Dad with a dilemma. In pressurized coolant overflow bottles the fluid level in the bottle MUST be higher than the coolant in the engine block. With gas mileage standards increasing the aerodynamics forced the hood design lower in the GM Pickup / Duramax. If the hood was lowered there wasn’t enough package space in the engine compartment to keep the traditional expansion bottle high enough for the sufficient fluid level to stay above the engine block. My Dad developed a tank where the Air AND expansion is located below the liquid, fluid and coolant.

This is my Dad’s explanation as to how the solution works:

It requires 2 separate chambers. The Air Chamber is below the coolant chamber (see diagram). When the engine and entire system is cold the upper chamber is filled through the fill cap (item #3). The fluid in the entire system will expand by 6% when the system is ramping up to operating temp (needing 2.2 liters for expansion). As the system expands the fluid has to go somewhere. With this design it expands up thru the blue path which is basically a 3/16” diameter “straw” that goes from the top of the fluid chamber to the bottom of the Air and expansion chamber. The pressure relief cap (item #4) is located at the very top of the lower chamber and the cap works in 2 ways. When pressure reaches 21 psi it relieves the air trying to push out. When the system cools down (there is a check valve) allowing the air to be pulled back in with no restriction. As the system expands the fluid is forced through the blue straw to the lower part of the bottle. It may fill up the lower chamber ¾ full. When the system cools down and contracts the check valve in the cap lets the air in and the “straw” “sucks” the fluid back up to the upper chamber. This allows the air to be contained below the fluid as the fluid has been sucked back to the top.

The patented cap protects user from hot liquid when removed while the system is hot. Users must NEVER open a coolant system when it’s pressurized and 200 degrees F or YOU WILL BE BURNED! How does this protect unwitting users from removal while hot? If you unscrew the fill cap when the system is hot the compressed air (21psi) with hot gasses and coolant will blow all over you. This solution protects the user by using three O-rings in the patented cap. The red trough (the other straw designed in this bottle) goes from the top of the lower expansion chamber to the 3-seal cap (specifically lower left) between the lower O-ring and the middle O-ring. This this zone is constantly pressurized when the system is hot. As you unscrew the cap when the system is hot and pressurized the middle O-ring falls off the step (just above it) connecting the red trough pressure relief to the hose. At the same time the UPPER O-ring is still engaged protecting the user that unscrewed the cap. The pressure from the lower chamber (hot compressed air and gasses) will be relieved through the hose. The bottle will then drop to 0 psi before the user can disengage the upper O-ring.

This is a new technique and an industry first. Prior to this design if the user unscrewed the cap for engine coolant while the system is hot scalding hot coolant and gasses blow the cap off soaking the user in boiling coolant. Not a safe thing to do. You have to let your car cool down before removing that cap. Sometimes you will see older guys putting a rag over the cap and remove it but that is still not safe. With this design the user is protected hot or cold.

This is the latest in my posts of what my Dad did during his career in the automotive industry. His primary focus is windshield washer and engine coolant bottles. He is an expert in plastic blow molding which is how these are made. I will be posting the process for such at some point in the future with pictures. My goal is to give an inside look into just how complex the automotive industry is and how much is going on behind the scenes. The bottles my Dad makes are just a small facet. I hope enjoyed this post.

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Comments (6)

  • I find this sort of thing fascinating! 😃

      2 months ago
    • That's why I'm putting this out there Eddie. Lots more to come - as I get them from Dad. It's a break right now so I may see a couple more in the near future. I'd like to churn these more quickly than I am but it's all up to his work load. I'm really...

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        2 months ago
    • Oh, I'm looking forward to more! 😃

        2 months ago
  • Wow

      2 months ago
  • WOW, purely amazing!

      2 months ago
  • That’s super smart. Really cool to see how some things that seem so simple are so brilliantly engineered!

      2 months ago