Official coolant overflow setup?

[longislandwrx]

The latest revision shows a long hose routing from the degas tank to the radiator and another to a rear mounted overflow tank, however I did not see any mention of what is done with the line coming from the radiator cap.

What is the official and proper FFR approved config?

thanks!

[Hindsight]

There are two lines on the radiator cap. One is on the filler neck. That goes into the overflow. The other normally goes to the degas tank on top of the engine. I can't remember if FFR provides hose and instructs you to connect that to the degas tank but in the 818, it's obviously a much further run. I did connect it that way on mine.

You can get rid of the front overflow tank by ensuring the radiator cap is higher pressure than the degas tank cap, then blocking off the barb on the radiator filler neck so it doesn't suck air when the car cools down. This setup will ensure any pressure issues are taken care of at the degas tank.

[longislandwrx]

yes they have you running a long hose from the degas tank to the barb on the top passenger side of the rad. I will cap off the overflow. Pretty sure the cap on the degas is 108 kpa = ~ 15.6 psi, and the one on the radiator is 137 kpa = ~ 19.9 psi.

the high performance STi cap is 130kpa so it would still blow first

makes sense.

[bompus]

Yep. I moved the 1.1 bar (~16psi) cap that came with my Megan Racing radiator to the degas tank, then installed an affordable Stant (10267) 20 PSI cap on the radiator. Capped the overflow port coming off the radiator cap, then ran a long hose from passenger side of radiator to the degas. I also have the VCP cooling system mod on the water outlet going to the degas. I have a "T" installed on the left nipple on the degas, and both mentioned hoses feed into it.

Haven't filled her up yet, but it seems like it would work well.

[STiPWRD]

I caped all of the lines coming from the radiator. Instead of running the recovery line from the radiator all the way back to the engine bay, I did Wayne's coolant mod and ran that line to the degas tank, it accomplishes the same purpose. I've ran and driven the car multiple times without overheating. I also used the airlift tool to suck the air out of the coolant system.

[FFRSpec72]

I capped off overflow from radiator cap but ran line all the way back to purge tank on engine and also added overflow tank off the purge tank on engine plus Wayne's mod

[Loring]

Curious what adding a separate, smaller overflow tank up front would do. Aside from saving having to run a burp line to the rear of the car.

[Mitch Wright]

Most of us have plugged the overflow nipple on the radiator and just run a overflow tank off the degas tank.

[billjr212]

Curious what adding a separate, smaller overflow tank up front would do. Aside from saving having to run a burp line to the rear of the car.

I did it this way, but will ultimately be changing it to just 1 overflow tank in the back with the lead from the top of the radiator as FFR now instructs.

The problem with 2 overflow tanks is that you can run into a situation where the overflow comes from 1 end (engine side) and the draw back on cool down happens at the other (front). Over several cycles you start to end up with excess in the rear overflow and not much left up front. (I'm a full winter separated from driving the car, but I'm fairly certain that is how it played out over time - may have been the other way around though)

[JeromeS13]

I did it this way, but will ultimately be changing it to just 1 overflow tank in the back with the lead from the top of the radiator as FFR now instructs.

The problem with 2 overflow tanks is that you can run into a situation where the overflow comes from 1 end (engine side) and the draw back on cool down happens at the other (front). Over several cycles you start to end up with excess in the rear overflow and not much left up front. (I'm a full winter separated from driving the car, but I'm fairly certain that is how it played out over time - may have been the other way around though)

This shouldn't happen if you use the correct radiator cap and upper coolant reservoir cap. The OEM radiator cap only vents pressure and does not draw coolant (vacuum) when the system cools.

[billjr212]

This shouldn't happen if you use the correct radiator cap and upper coolant reservoir cap. The OEM radiator cap only vents pressure and does not draw coolant (vacuum) when the system cools.

I used reservoir caps on both. If I used the regular radiator cap up front, the problem would be worse because the front would expand to fill the second overflow, but would never draw back from it.