Hey everyone, yet another question...

Is the coolant overflow tank supposed to have a large opening at the top that goes straight to atmosphere? Both the tank on my car and a replacement I bought both have it, and as far as I can tell from Youtube videos, other G35s also have this vent.

As far as I can tell, the place where the overflow tank's tube connects to the radiator cap has no valve in between it and the radiator itself, as you can pour coolant straight into the system there after removing the cap.

This is very puzzling to me because 1. that means the coolant can be contaminated by dust in the air and 2. the coolant runs at atmospheric pressure, so at high altitude it would have a low boiling point. I've never seen a car that doesn't have a pressurized system, nevermind an unsealed system.

Is there supposed to be something plugging that vent?

 

Okay now that I think of it, the radiator cap is the pressure relief, and the coolant overflow tank is only there to hold coolant that spilled out, right? So it doesn't really matter that the coolant in the tank is exposed to atmosphere, right?

 

Correct!

The radiator is pressurized with the rest of the system. The overflow is not.

When coolant gets hot and expands, it overflows into the overflow tank. When the system cools, it sucks the coolant back in.

 

Is it not a concern that outside contamination gets into the coolant system then? I just have a hard time understanding how it is acceptable to let dust into the system. My Toyota MR2 Spyder had a pressurized expansion tank with a pressure venting cap on it, no air could get in at all.

 

What exactly do you mean that it's open to the atmosphere? Take a picture and post it, I'm pretty sure you're MISSING some component.

Radiator is sealed, overpressure goes off to the coolant reservoir which is also sealed with the exception of the overflow pipe which all coolant reservoirs have.

This system is no different than any other system, even odd looking systems like the Chevy/Ford ones that don't have a radiator cap are still functionally similar.

Radiator expansion goes to a reservoir, as coolant cools it draws from the reservoir, reservoir has an overflow.

 

This is the used tank I bought off Ebay, my tank also has this hole at the top, and in Enthusiast Auto Care's coolant service video the coolant tank also has this little vent poking out with nothing attached to it.

The part in focus is the interior of the tank. Water comes right out when you pour.

 

Thats how my reservoir looks -
I filled in that hole on the top w/ RTV & added a 5/16 barb to the side and ran a hose down to the splash shield. That way, should coolant overheat into the reservoir, the coolant will dump onto the ground and not make a mess all over the engine bay.

 

Yup, thats just the vent for the overflow tank. Most cars will have a hose connected to it so it can drain out in case it fills up and overflows. Its also there to prevent an air vacuum lock when fluid gets sucked back into the radiator. U are hardly gonna get any dust going in there....definitely not enough to have an impact on anything.