Smoke coming from engine and coolant everywhere!

So I�m on a road trip abroad currently and this just happened. I�ve been driving for a good 5-6 hours on the motorway today and seemingly no problems. Engine temp just above 80 degrees and no smells weird noises (I checked oil/water this morning as I did a good 7h run yesterday, and everything looked like it should). So I come to the town where I�m staying and I park up on the side of the road to look for a car park. I keep the engine running as it shouldn�t take long. And then I see a lot of white smoke coming in the mirror. I first think it�s exhaust but shouldn�t be that much at this point. So I check the temperature and it has jumped to a 100 degrees which seems odd. So I immediately turn off the engine and pop the cover open and go out to open it up and it�s just coolant everywhere and smells a little bit burnt also. Waiting for it to be towed away now to a workshop. How worried should I be?

I wouldn't be worried at all, as long a there was no "flashing warnings" on the dash prior. The shop will just find the busted hose/failed water pump and repair, and have you back on the road soon. The good thing about Porsche 996 ( and some other high end cars), is they have low coolant and low oil warnings. I tell my Children and Grandchildren that old cars run on coolant and oil,, NOT gasoline. You can run completely out of Gas and just put some in and crank and go, but if you run out of oil or coolant, you KILL THE CAR....

Quotes source post: 18079045

Well, before I turned off the engine I didn�t see any warnings. However, I reluctantly turned on the engine to drive up the flatbed. And then there was a flashing warning light at the temperature gauge.

Doubt you got it hot enough driving it up the flatbed to cause damage. Just make sure they don't ever start it again until it's looked at. Also this is a good idea of when to put your tow hook in. This car should never be started again until it's healthy again. It should be pushed around and or winched onto a flat bed.

Quotes source post: 18079150

Indeed, it had been about an hour until the flatbed came so it had cooled down to about 50 degrees or so. I only had it running for 30 seconds maybe, just enough to drive it up the truck. it�s now at a Porsche Center so hopefully they�ll take good care of it on Monday.

Had a similar experience arriving at the airport one day. Little warning and then hemorrhaged all the coolant when I parked in the parking lot. Turned out to be the water pump. Straight forward fix. Let us know how it goes.

Quotes source post: 18080095

I hope for something similar! But haven�t been told what it might be yet. Just not sure if they have been working on the car for hours today and not found the issue or just haven�t worked on it at all. I just get �we�ll know more soon and will be in touch� answer so getting a bit frustrated

Quotes source post: 18079045

+1

Driving up onto the flatbed after setting that long was probably ok.

So they have finally got around to look at the car. They say it was the cover for the coolant system that broke. Not sure what they mean really. It can�t be as simple as the screw cap for the coolant tank right? cause that is also brand new.

Unless the wrong cap was used or the more serious problem of backup pressure

The day I bought my 996 and drove it home, white smoke poured out the back when I pulled into my driveway. The coolant cap was nowhere to be found.

Quotes source post: 18085908

I would confirm they used a factory coolant tank. Aftermarket tanks are known to have cap thread issues. If you have an aftermarket tank, be prepared to have continued issues.

Quotes source post: 18085908

I had a cap fail. Caused me some leaking. Look at the cap as being as durable as the Factory aos. You just never know when it will go, but it will go. I have an extra new factory cap in the car just in case. You will know something is leaking in your cooling system because you will begin to smell coolant. First thing i do is replace the cap and then go for a drive to see if it goes away. If not, it's most likely the coolant tank. Just happened to me 2 weeks ago. I replaced the Cap. Drove the car a few times. Coolant smell was still there after a few 30 minute drives. But no puddles under the car. Car is now in the shop for scheduled service and they are going to find the slow leak. Factory water Ppump and coolant tank are only 4 years old.

Quotes source post: 18086182

Consider one of these: https://lnengineering.com/products/p...-tank-cap.html 3x the costs, but peace of mind.

Quotes source post: 18086230

Thanks Tex. I think I will. Forgot about those.

Quotes source post: 18085938

What do you mean "backup pressure"? I am fighting a coolant leak on the left hand side of the engine. I've replaced the expansion tank with genuine Porsche, new hoses put in today. Looks like coolant is running down the inside of the coil pack heat shield and draining out on the floor from the front edge of the shield. I am at a loss for finding the leak. After replacing the hoses, I refilled the system with an Airlift II. Seemed to work well. Coolant was not coming out of the overflow tube, or any of the hose to engine/tank connections after the test drive. Any ideas? Puddle after 10 mile test drive dropping from front of LH side of engine Most of the leaking coolant was running/dripping from the lower LH corner of the coil pack heat shield.

^^^Left front side of engine = AOS�

Quotes source post: 18135131

I agree�AOS.. I had similar fluid and was AOS. It would not leak right away but after engine was warm and pressure built up in the system. Good luck! Will

I have always wonder WTF coolant is fed to the AOS?

Quotes source post: 18135322

Heated coolant is constantly fed to the AOS to assist with condensation/vaporization of the oil fumes from the engine crankcase. In cold weather climates it is necessary. In warm weather climates, I don't think it really does much. But...the coolant hoses to the AOS are prone to leak, mostly at the junction next to the alternator and at the AOS. One way the OP could check is to use a hose crimp on the AOS supply line. If the leak stops, then there you have it. An aside, I had to replace my AOS not due to the hoses or fittings leaking. The AOS diaphragm plastic housing cracked open.

UAOS time and don’t look back

If I am not mistaken, the UAOS mitigates the coolant issue.

Is it possible it could be something else? I just had the car in my indy shop for a RMS and IMS bearing replacement. The mechanic said he looked at the AOS while he was in there and said it looked good and didn't need replacing at this time. Is it possible he could have missed evidence of a coolant leak there? I'm frustrated and weary of replacing parts that are not the problem. At least I have a new expansion tank and a few new hoses. I should mention that when generating the vacuum with the Airlift II, the system held a -24 psi vacuum for at least 5 minutes before I turned the valve and let the coolant flow. What could be leaking profusely while under pressure, but still hold a vacuum to atmosphere? Also, there is semi-dried coolant residue on the furthest rear coil pack, nowhere near the AOS. There is no visible leaking on the line bundle going from the alternator forward to the AOS area that I can see with a flashlight and mirror. After filling with the Airlift II, it was slightly overfilled and I needed to suck some coolant out of the tank to bring it down to the Max level, cold. Then I opened up the burp bail on the valve and went for a 10 mile drive with the aftermath shown in the photos above. I let the car cool down a bit, and the leak from the heat shield was reduced to a rapid drip, I loosened the cap slowly and let the pressure out. The drip ceased and the coolant level rose in the tank to the bottom of the cap's threaded neck. Could there still be an air pocket in the system? While driving, the temp gauge hovered on the middle of the 0 of the 180 mark. When I pulled into my garage, the radiator fans were on. Ambient temp was 90�. I am loathe to replace the AOS only to find that it wasn't the problem.

Quotes source post: 18135819

I would let it cool down, put the cap on tightly and then put the little metal piece in the up position. Drive it around and monitor what you see, don't take the cap off. I remember once I got my second expansion tank in my car, I ended up putting the level slightly lower than I thought what it woudl be to get everything to be in harmony. If it's all good after 4 or 5 spirited drives and cool downs, put the metal piece back down and leave it. There is a chance you don't have a leak.

You originally said �left front of engine�� This is where the AOS resides� it�s known to spring leaks. Of course it also has lines that carry coolant to it - it very well could be one of them or both. I understand that the shop said the AOS �looked fine�, but what exactly does that mean? Short answer: NOTHING! Do yourself a favor - after figuring out exactly where your leak is, replace your AOS with a UAOS, and be done with it. Good luck 👍

Well... You have a rather large coolant leak. Good news is it's coming from somewhere along where the coolant flows. Could be from anywhere, but a pretty good indication may be from directly above where the coolant sits on the ground. Sure it could be the aos which is a brittle piece of plastic that is known to fail frequently and often. Could be a deteriorating hose or anything. But Deporto is right. Whether the leak is coming from your aos or not, do yourself a favor and get rid of the stock aos like I did in 2006 after 2 failures in 4 years. I replaced it with the motorsports aos, which i then replaced with the uaos, which is light years ahead of the motorsports aos in functionality, dependability and ease of service. And the motorsports aos was pretty damn good. Oem aos, not so much. Whatever direction you go, let us know the outcome. The vast majority of us want to see all 996s running strong. They are great cars.

Quotes source post: 18086182

FWIW, slow leak came from a hose that couldn't be found by just eyeballing the car from below and above. It was found after my indy dropped the engine to replace the ims retro, rms, motorsports aos with the UAOS Track version, oil cooler, as well as an in depth look over of the engine, cooling system and various other bits. Don't forget, these cars are 20+ years old. Everything plastic and rubber become brittle. As a side note, my motorsports aos was tested a month earlier and everything was fine. then a funny thing happened 2 weeks before my car was scheduled to go back to the indy for the above referenced service, the motorsports aos failed when I started my car. Crazy, but timing was perfect and Skip shipped me the UAOS and the car and I are very happy.

Quotes source post: 18079004

OP, did you ever find out what the exact failure was? Hope all is fixed and you are back motoring again.

An engine drop (or gearbox drop) without replacing the AOS is false economy. It's another $150 to save $1,000. As for your coolant leak... do a pressure test with the wheel removed, heat shield removed (like you are doing a spark plug changed). You will find it.

Well yesterday, I put the cap back on tight and took the car out for a short drive to bring it up to temp. My intention was to start it leaking again and clamp off the coolant feed and return lines to the AOS. They are easily reached in the engine bay. As suggested by DBJoe996, if the leak stopped, it would pretty much indicate the AOS as the culprit. But, once I got it all warmed up and back in my garage, it wasn't leaking, not a drop. Geez! Now what. I guess I'll just have to keep an eye on leaks and coolant level as I drive it around. I kinda doubt it just fixed itself. The obvious question here is, if there is too much coolant in the system, is there another vent release to the atmosphere other than the tank cap itself? (aside from a cracked AOS fitting)

Why take the risk change out to the UAOS and be done with it

There is a black pressure/safety valve at the back of the tank�You probably didn�t get it up to full pressure/temperature on your test drive�

Can you supply a photo of this valve? Are you referring to the valve just behind the fill cap? The one with the wire bail on top? That valve does not vent to the atmosphere.

Not yet. I do have an appointment with Autohaus Tucson to diagnose the coolant leak next week. I'll be bringing it there if I cannot find it myself.

Thats the one. I believe it does raise and lower on its own, and during a purging procedure, can be set to fully open to allow for expansion and contraction. Here�s one thread that discusses it: https://rennlist.com/forums/996-foru...-bleeding.html

Here you go: https://rennlist.com/forums/996-foru...lve-works.html

Took the car out for a longer drive and when back in the garage it was leaking again. I clamped off the AOS feed and return lines and it didn't make any difference with the leak. So, not the AOS. I got my mirror-on-a-stick out and a good flashlight and started looking at places not visible from top or bottom. Then I found it! Turns out it was dripping coolant from the large barbed nipple at the bottom of the expansion tank. Looked fine from above. Coolant would drip off the hose down to the inside of the coil pack heat shield, run down to the bottom lip which would carry it to the front and pour off to the floor from there. Mostly all hidden from view. Turns out that the barb on that tank fitting only goes around 180�, not 360�. When I put in the new hose, I pushed it on with the clamp in a clamp pliers. I must have let the clamp go before it was fully past the barb and it wasn't fully sealing all around the hose due to the partial barb. Apparently, when putting a vacuum on the system the hose would get sucked down into the nipple and make the seal. But when under pressure, the hose would expand and let coolant by the barb. It probably only has 1/2 a barb due to tooling requirements in the mold. Anyway, I got a clamp pliers (cable operated remote style) on that clamp and was able to push it towards the tank, past the barb to get a full 360� seal. I put everything back together (this is about the 7th time the air pump and air cleaner box have been in and out of the engine bay this week!) and took it out for an extended drive. NO LEAKS!!!!! I'm a very happy camper. I'll be cancelling my appointment at Autohaus Tucson. Yay! PS Sorry for hijacking this thread...

That's good news!