Coolant Recovery
By Mark Lambert
Lambert Auto, Nashville TN
Have you ever wondered why newer cars have coolant recovery tanks incorporated into their cooling systems? Environmental protection, you guess? Well, not exactly, although that is a benefit. One reason is this: A radiator, when combined with a coolant recovery tank, is always full.
Properly mixed (35-50% anti-freeze with distilled water) coolant expands as much as
15% by volume when heated to operating temperature. As the car cools after shutdown, the coolant begins to contract. That’s why, when checked cold, the radiator always has a sizeable volume of air at the top.
The coolant recovery system gives the radiator the ability to always be completely full. Upon warming, the coolant expands and is pushed into the recovery tank rather than out onto the road. Then, upon cooling (contraction), it is sucked back into the radiator through the small flapper in the bottom of the radiator cap.
Thermal dynamics and convection theories are pretty involved stuff, but here’s the interesting part: If the radiator is full from the start, the thermal cycle is flatter and has a lower ceiling. Instead of having all of that air in the radiator, you have coolant. This larger quantity of coolant allows a greater convection rate and gives you, in effect, a bigger radiator. If you have a bigger radiator, the entire cycle has a lower ceiling.
The coolant recovery system permits the use of a smaller cooling system (smaller radiator, less coolant, less weight, less cost) and has the same thermal dynamics as a larger, unrecovered system. Less cost! There’s the other reason for the recovery system in new cars. I recommend placing a TR-7 recovery tank and bracket under the bonnet on the passenger side bulkhead. It fits beautifully. No drilling is necessary. Use an existing screw hole from the steering column blanking plate. Routing 5/16” copper tubing down the frame rail and crossing it under the radiator, adjoin it to the existing overflow tube.
Although my BN-2 had no high coolant temp problems, I have noticed a slightly reduced coolant temperature. The best part is no longer having to twist down (front hinged bonnet on the BN-1 and 2) under the hood prop rod with a flashlight to check the coolant level. Now I just glance at the translucent recovery tank.
Happy coolant recovering.