S4 GXL, 207k miles on engine, original engine as far as we can tell.

Last night on our way to a Flyers game I redlined it getting onto the highway and about 30 seconds later the add coolant buzzer came on. It went away after about 5 seconds and then came back on. I pulled over to look things over, no obvious leaks in the engine bay. Coolant reservoir was full and I didnt remember it ever being that full. To be safe, we got off at the next exit and turned around to head home. I gawked at the coolant gauge trying to see if it was moving up, however it did not seem to go up even though the add coolant buzzer was on. This seemed fine to me as maybe it was just a tiny air pocket. It wasnt until we got off the highway that the needle seemed to have budged upwards, at that time I turned the engine off to try and stop building up heat. We sat at the 2/3 lights with the engine off. I noticed I heard some bubbling from under the hood. When I pulled away there was a small puddle on the ground. I coasted it through a neighborhood until we hit ours and thats when the gauge had obviously gone up, but not gone up super high, no where near the top of the range. I had someone tell me that sometimes the rad cap neck warps overtime causing a pinhole air leak to where the coolant will expand and push into the overflow, but allows air back in instead of sucking the coolant back in. This is best case scenario...Worst case and my fear is that its a coolant seal.

Any ideas? Where to start?

 

When cold remove cap and start engine and if coolant starts coming out fast as engine warms up you most likely have a blown water seal

 

Find the source of how the coolant is getting to the ground. That's where I would start. You can rent a coolant system tester at Autozone, checker, orielley, etc...... Pressurize the system and look for leaks.

 

Only thing i would add to this, is if it holds pressure cold, leave pressure on it and start it and let it warm up (don't overheat it) and watch the pressure gauge as it warms up, if it starts to lose pressure, obviously you have a leak

 

It's toast. popped rad cap. Had smoke pouring out of the cap area. Car hardly wanted to start, when it did it was on one rotor until I revved it enough to clear the coolant out. Rebuild time.

 

If you're going to let it sit, drain the coolant out, start it for a minute, then shut it down after its running on both rotors. You don't want it sitting in the engine to get rusty!!!

 

and or dump a bunch of oil in it. iron seals + iron rotor + water = one rusty blob

 

Yep. it's on the list of things to do.

Such a shame too because it had 105 psi on every face still!

 

Let's hope it's a quick soft seal rebuild then!

 

Thats a real shame, but of all the ways this engine could fail is this really the worst? Unless the wall holding the water seal has failed or you leave the engine for a few years to rust away theres a good chance this will be a quick rebuild

 

I emptied the coolant out today and ran the engine for about a minute. I think the first time it was ran it must have flattened the apex seal springs because its noticeably harder to start compared to before the problem.

 

My money is on a broken seal groove in one of the irons.

Might be a wet (coolant) spark plug

 

I would think without the coolant sensor submerged in coolant the ecu would be getting a false reading causing hard cold starts.

 

Soft seal rebuilds are generally cheap and easy rebuilds in comparison. Think of it as a head gasket replacement, as that's essentially what it is. Also, not sure what would cause you to also damage an apex seal, people drive with broken coolant seals for months without damaging apex seals. The hard starts are typically because the water is diluting the fuel during combustion which is why it runs so rough while it's smoking off all that coolant.

 

Apex seals arent damaged, just the springs. When the engine overheats the apex springs lose their springy-ness and flatten out from what I've read.

You are probably correct about the iron's groove breaking. Still a lot easier to find an NA iron than a housing + matching weight rotor

No coolant on the sensor is a possibility..who knows.

I'll update this in a few months when I get the engine taken apart!

 

put oil in it now please.

 

I'm considering being lazy. I premix it roughly 1oz per gallon of gas on top of the OMP. Would unplugging the coil packs out and turning the engine over for a minute or so suffice?

 

You didn't mention an engine overheat, which leads me to believe that the springs aren't flatten out. I bet you that the engine will start up fairly easy with new (or freshly cleaned) spark plugs.

On any case, the circumstances suck, specially when the engine had a healthy compression

 

no, drain the water, or put oil in it.

 

make sure your draining the coolant from block fully by removing the bolt thing by the driverside motor mount, vs just draining the bottom of the radiator.

 

Thats exactly what I did. To go one step further I lifted the passenger side of the car to make sure it forced out as much as possible.