Coolant Overflow Pressurized??

[psychlow]

Should the coolant overflow bottle on our cars be pressurized?

Reason I ask, is the cap on mine does not seal to the bottle. Thus, when the car pushes the coolant into the bottle, the cap pops off and the coolant evaporates. This empties all of my coolant into the atmosphere, and my car overheats.

I figure if I fill the overflow bottle up to the line that I'm supposed to, it should cool the incoming coolant sufficiently to keep it from evaporating, correct? Or is the overflow bottle supposed to be tight enough so it can be pressurized?

 

[dave99gst]

it should be sealed.. the bottle is a give/take system .. it takes coolant when it needs it and overflow into it when theres to much

 

[psychlow]

OK... so has anyone here opened their overflow when it was hot and a bunch of steam shot out? I'm wondering because it doesn't have a warning on it telling you not to open it when its hot, yet the radiator cap certainly does.

 

[andymoraitis]

There's an easy fix for the cap popping off from your expansion tank. Simply take a small strip of duct tape and wrap it around the lip. It'll work fine and you won't have to worry about coolant evaporation.

Hope that helps

 

[Forced4]

The cap has to vent some. If it was sealed it would pop off because the pressure inside would change. The cap has tiny pinhole in it. If you look close you can see it. Make sure it is not plugged. Also make sure you have a good "rad cap" yea, I know it's not on the radiator. If it's weak you will send a lot more volume to the overflow bottle and that could be poping the cap off. My 91 used to over heat and loose coolant. The guy bought it from kept 2 gal of coolant in the back. I bought a rad cap for like $7.95 at a mitsu dealer and, go figure.... No overheating and no coolant loss. Some times the smalles thing can cause the biggest problems.

Good Luck
Rich
Forced 4

 

[Forced4]

...Oh, one more thing. If it is seriously being pressurized, you could have a bad head gasket, cracked head, cracked block or something along those lines. I am sure you would notice a lot more than higher temps and coolant loss. Like, it running like crap for example.

Ok, done now.
Rich
Forced 4

 

[psychlow]

Well, it does run like crap, but the compression is pretty consistent among all four cylinders, so I'm not thinking it's that yet. I think it has a lot to do with the fact that I don't have an oxygen sensor hooked up because the PO FUBARed the wiring.

Yeah, the first thing I need to do is fill up my coolant the RIGHT way - IE, take the time to burp the system and fill the overflow tank like it should be filled. I just didn't get a chance to do so last go-round, so I think that's where my problem stems (air bubble behind the thermostat, probably, so it didn't open properly).

Thanks everyone for your help.

 

[Defiant]

Originally posted by psychlow
Should the coolant overflow bottle on our cars be pressurized?

No. It could be done with a bucket if it weren't for spilling. It's just an expansion space regulated by the radiator cap. If you have any kind of boiling going on in there, replace your radiator cap.

Reason I ask, is the cap on mine does not seal to the bottle. Thus, when the car pushes the coolant into the bottle, the cap pops off and the coolant evaporates. This empties all of my coolant into the atmosphere, and my car overheats.

It should hold on just by gravity. And, there's supposed to be a siphon tube reaching down to near the bottom of the bottle. There should be a second overflow tube that comes out of the cap and runs down past the resevoir and below the side of the radiator.

I figure if I fill the overflow bottle up to the line that I'm supposed to, it should cool the incoming coolant sufficiently to keep it from evaporating, correct?

No. That's just to prevent the cooling system from sucking air when it cools down. If you fill the bottle to the top, the engine will press out the extra water and if healthy, will find its own correct level after a couple of heating/cooling cycles. If you're missing the siphon tube in the cap, the engine will force out expanded hot coolant but suck in air when it cools, getting air into the cooling system.

Or is the overflow bottle supposed to be tight enough so it can be pressurized?

No. Again, it could be a bucket. It's only blow molded like a milk carton. It wouldn't survive pressurization for very long.

 

[psychlow]

Thanks, Defiant. I was wondering where you were last night.

 

[RiceKiller_TSi]

Get your head gasket checked.
Oh, nevermind, somebody beat me to it.

 

[Umaro]

Ok, I just bought my 1g tsi awd and I have taken it out twice for a little run around the block, the second time I pushed it kinda hard and when I got back I thought something was seriously wrong cuz it looked like smoke coming out from underneeth my hood.

I opened up the hood and it was coming from directly under the radiator cap BUT there was also a little put of water ON the radiator cap, so Im assuming the smoke was just water evaporating.

Now, is this normal, or maybe there was too much coolant?

Any thoughts.

(I decided to just post in this thread since it was on topic)

 

[psychlow]

Yeah, when it spits coolant, everyone suggests that, so the thought had crossed my mind. Compression checks out OK, though, so it's not that - compression would definitely be low if it were leaking into the coolant enough to overpressurize the system.

Also, I've drained the coolant multiple times, and every time it comes out pristine - not even a trace of oil.

But, thanks for the suggestion.