Opening coolant reservoir while hot?

[Propaganda]

Hi,

I recently got a coolant leak, it didn't occur before. I've done some digging on the forum and some threads mentioned getting air into the coolant system?

The other night after driving around for about 20 minutes, I parked in my driveway and opened the coolant reservoir, it make a pressurized hissing sound. Am I not suppose to do this? Did this cause air to get into my system and thus giving me a coolant leak? Any help is appreciated. Hopefully I can get it on a lift soon to inspect the Aux pump and exact location of the leak.

So my main question is, in our B5 S4 do we wait until the engine is fully cooled down to open the coolant reservoir.

Thanks!

[getslideways]

No, unscrewing the coolant expansion tank fill lid does not allow air bubbles into your coolant system anymore than unscrewing your gas cap allows air bubbles into your fuel lines.

The cooling system is under pressure, which raises the boiling point. So the hissing you are hearing is air exiting the coolant tank, not entering it. The main reason you want to wait till its cool before popping the lid is to prevent the coolant from rushing out (sort of like cracking the lid on a shaken soda) to keep you from making a mess, or getting injured by hot liquid.

[Propaganda]

Thanks for the quick response. I kind of figured that, but I was hoping that was the cause of my coolant leak. Looks like I'll have to do some more digging!

[getslideways]

Air bubbles in a system can cause overheating issues, as it can inhibit the flow of the coolant through the system, but it will not create a leak.

Can you tell what area of the engine bay the leak is coming from. Such as If you look under your car after its parked, can you see where the drip or puddle is forming? It might help narrow down the list of usual suspects.

[Propaganda]

I checked this morning, sadly I can't lift my car up due to it being lowered. I'm going to try to get it on a lift this weekend. The leak appeared to be coming from the rear of the engine.

[getslideways]

Since you already have an appointment for a lift this wont help you, but in the future, you can drive it onto a block to gain clearance for a jack, thats what I do on my lowered vehicles:

[Propaganda]

Why didn't I think of this! My in-laws have a lift :) He however refuses to touch the Audi because he's afraid of all the electronics. He is more of a vintage muscle car guy (60's camaro/mustangs).

[[email protected]]

Get a 6' section of 2x8, cut it in the middle on an angle and you have a pair of 3' ramps for your lowered car.

[Timtheguru]

When hot the cap will keep pressure on the system, just crack it slowly to release the pressure out the overflow. It's kind of like opening a 2 liter bottle of soda that a pizza delivery guy brought to your house. Just screw it back on if you see an abundance of coolant trying to escape.

The cap also has a pressure valve in it so when it goes bad that could also be leaking, to where the coolant goes out the overflow. The O-ring on the cap can also go bad causing similar behavior as the valve.

[Propaganda]

I couldn't access the lift today, but I'm going to attempt the 2x8 boards tomorrow. I'm also looking into a low profile car jack. The coolant appears to be leaking from the front/center (parallel to where the two front wheels touch the ground).

It has leaked enough in the past 2 days to cause the reservoir about 1/4 of an inch below the minimum line. I checked around the engine and no sign of pink crusty stuff, so I'm thinking it's not the Aux water pump. My guess would be either water pump or some random coolant hose. Great first week of owning an S4 :)

[getslideways]

cut an angle on your blocks, to make a mini ramp. This will keep the tire from grabbing the top edge and kicking them up into the bottom of the car.

[manilikecars]

just build this. works great. 30 bucks is cheaper then 200+ race ramps.

[Propaganda]

just build this. works great. 30 bucks is cheaper then 200+ race ramps.

Did you glue those boards together? It doesn't look like you have any nails or screw through them.

[rippin'av]

just build this. works great. 30 bucks is cheaper then 200+ race ramps.

I built something similar to this. Has been so helpful.

OP, its going to be hard to see where your leak is unless its a big leak. The leak could be anywhere and running down a hose and making it hard to diagnose the source. If its not obvious or visible from above and you don't mind popping the front off take a look at your water pump or thermostat. Very common leak areas. Its a PITA just for a small leak but these cars are built so crowded its the only way sometimes. Good luck!

[manilikecars]

They are nailed together.

[hendrj5689]

So do you guys use those ramps just to get it off the ground enough to get a jack under it? It doesn't appear it would be high enough to much wrenching.

[manilikecars]

I wrench under it if I can. great for oil changes. but for big jobs id use jack stands.