Hey all,

So I did my HGs about 10k miles ago, I haven't had any problems. However lately I noticed the waterfall noise returning. I checked my coolant and it was a little low, so I've gone back on high alert with the coolant watch. Today I tried to bleed it. I opened the cap and a good bit of air escape. I proceeded to raise the reservoir to bleed it but didn't get any air out of the bleed screw. So I topped it off and went on my way. I drove across town to fill up on gas. When I got there I double checked everything, but sure enough I had air in the reservoir again, and when I took the cap off I noticed some coolant leak out of the overflow hose.

Could this be a problem with the reservoir or cap? Or maybe something worse? Besides this it's driving fine.

 

Raise the front end. Drive up a hill and let it run.

 

You drove across town and had air pressure in the reservoir? I don't see anything wrong with that, the coolant system presurizes under normal use doesn't it?

My cap like all the other brittle plastic had broken a piece off, they're cheap to replace $10. Can't hurt to keep one on hand anyways.

 

There shouldn't be air in the coolant system. Water pressure is different. Air means bubbles (the famous waterfall noise in the dash) and prevents the coolant from completely filling all coolant passages, leading to inefficient cooling.This is why they have a bleed screw in the original design.

My only concern is how the air could be getting into the system.

 

there IS air in the coolant system. the coolant doesn't come all the way to the top of the reservoir. there's air at the top. if the system becomes pressurised -- as it should -- then that air will be under pressure.

 

Right, but then once the engine has stopped running and the water pressure returns to normal shouldn't that air return to normal as well?

If you hear a whooshing sound when opening cap wouldn't that imply air was being added into the system?

 

no. it stays pressurised for a while. that's part of what the cap on the coolant bottle does. if the pressure drops quickly, there's a leak in the system somewhere.

 

Hmm, that would put my fears at ease. I can see how it makes sense that if it's maintaining pressure then it's not leaking out anywhere. Not sure why it all the sudden developed the waterfall though.

 

Air getting into the reservoir is not the same as air getting into the "system." The problem is that coolant is escaping. Start with a new reservoir cap.

 

right. if the waterfall appears when you haven't done anything, then there's a leak somewhere. reservoir cap is a likely culprit and is easy and cheap to replace.
i was just trying to point out that opening the cap and hearing air escape is normal, and does not, in and of itself, indicate that there is a problem.