[Mark114]

Originally Posted by LSA

Right, so when you attempt to apply vacuum to the top tank (to refill the system) how is air not pulled in through the cap of the lower tank? Is the crappy cap for the lower tank air tight? I would think it is not by design, otherwise it’d pop off when fluid was forced from the top reservoir into the lower reservoir.

The lower chamber is vented. The vent holes are facing the strut tower so you can’t see them easily. If you overfill the lower vent chamber then it will drain out of the vent holes.

[LSA]

Granted, it’s off topic a bit.... but the question remains.

If you attempt to apply vacuum to the upper chamber, it seems as though the lower chamber would “leak”..... let air in. Wether through the cap or the vents.

[Z28GTOSSMike]

The lower tank doesn't need to be air tight. It's just a reservoir to catch any coolant that gets pushed out of the upper tank which is part of the pressurized system if the pressure gets above the cap pressure rating. As the system cools and contracts it will pull coolant from the lower tank like drinking with a straw. Best I can explain it. Just top off the upper tank when the engine is cold and make sure the bottom tank is between the lines.

[Mark114]

Originally Posted by LSA

Granted, it’s off topic a bit.... but the question remains.

If you attempt to apply vacuum to the upper chamber, it seems as though the lower chamber would “leak”..... let air in. Wether through the cap or the vents.

There is a hidden fill tube between the chambers that is built into the tank. The fill tube runs from the large cap on the upper chamber down to the bottom of the lower chamber. Excess pressure and air/coolant is pushed up through the pressure relief valve in the large cap. It is then vented into the lower chamber through this fill tube. When the engine and coolant cool it pulls vacuum from the upper chamber through the fill tube to the bottom of the lower chamber. That will draw coolant (if available) from the lower chamber back up into the upper chamber.

[Z28GTOSSMike]

Originally Posted by Mark114

There is a hidden fill tube between the chambers that is built into the tank. The fill tube runs from the large cap on the upper chamber down to the bottom of the lower chamber. Excess pressure and air/coolant is pushed up through the pressure relief valve in the large cap. It is then vented into the lower chamber through this fill tube. When the engine and coolant cool it pulls vacuum from the upper chamber through the fill tube to the bottom of the lower chamber. That will draw coolant (if available) from the lower chamber back up into the upper chamber.

You explained it much better than I did.

[CRBWS6]

What type of evaporation rate are others seeing from the lower tank?

My upper and lower tank looked exactly like the OP's when I bought the car a few months ago.

I filled the upper tank and brought the bottom tank to fill line per the manual. This was 36 oz total add of 50/50 Dex.

Now, 1000 miles later the level has dropped about 1/2" - 3/4" below the fill line in the lower tank.

How does this compare? It seems like a greater rate of evap than my other vehicles with vented overflows.

[funked1]

Originally Posted by CRBWS6

What type of evaporation rate are others seeing from the lower tank?

My upper and lower tank looked exactly like the OP's when I bought the car a few months ago.

I filled the upper tank and brought the bottom tank to fill line per the manual. This was 36 oz total add of 50/50 Dex.

Now, 1000 miles later the level has dropped about 1/2" - 3/4" below the fill line in the lower tank.

How does this compare? It seems like a greater rate of evap than my other vehicles with vented overflows.

I have had to add coolant to the lower tank twice in 15k miles. It went from half full to maybe 1/4 full. I live in a very dry climate, so I am assuming it is just evaporating through the vent.

[CRBWS6]

Since posting earlier in this thread, I have checked the coolant level on three other SS cars.

Each car was warmed up and the owners had not previously added fluid, or even checked it.

Car 1 (15k mi): Lower tank: Empty, Upper tank: 90% full
Car 2 (15k mi): Lower tank: Empty, Upper tank: 50% full
Car 3 (5k mi): Lower tank 1/2" below fill line, Upper tank: 100% full

This just serves as a reminder to check your coolant!

The dealer installed FSB is part of the problem as it hides the lower tank fill tube pop-off cap.

[Invertalon]

My lower tank is about 1/2 full (from the "full level", not the entire volume of the tank). It was higher when I first got the car a few months ago, I'm pretty sure, so it has evaporated off some. Top tank still 100% full, of course.

Will top it off tomorrow (fluid en-route).