Coolant leak from cap???

Yesterday i drove about 15 min and stopped at a stop light to only see a whole bunch of smoke (steam) from the engine area. i pulled over, opened the hood and saw lots of antifreeze coolant pouring out from the expansion tank cap. The car was not overheating when i was driving. I poured water in it and drove it home and it seemed fine? has anybody had this happen to them? what could be the problem? i did some research on it and people say it could be the expansion tank or cap? can it be true? the car only has 35k miles

I would begin here: http://www.pelicanparts.com/catalog/..._pg2.htm#item8 My 99 C2 had a minor leak at 41K. The OEM radiator (expansion tank) cap has been since redesigned:996-106-447- 04- M100. $25.00 + shipping. Super fast delivery. OEM from factory I believe was: 996-106-447- 01 -M100. Good luck.

Yep......try a new cap. Just replaced mine when it did the same thing.

I just had a conversation with a service manager Saturday, he told me that was a common problem for the 996, so yes I'd start there.

ok yea bought a newer cap from the dealership and i guess it fixed the problem

Quotes source post: 3237778

Quote: Just a heads-up. Keep an eye on any small drips coming from connectors. I replaced my cap and stated getting a small drip from the front connector at radiator. When I took it in they performed a pressure test and no leaks... Tested the new cap and it wasn't venting. Insisted on testing the new cap they where about to put on and the following 3 caps where also not venting at properly! Go figure... Cheers! Sid.

yea, replacing the cap should help....if your tanks have a yellowish in color, then you might want to keep an eye on it cause they are known to have small crack underneath which will also leaks under pressure

Hopefully u added mineral free water

The caps do not vent unless they are bad. The vent is the black plastic thing, with a metal bale, on the expansion tank behind the cap.

Quotes source post: 3241871

Quote: OK.... Not for nothing but hmmmm I think you should check your facts. The the "bale is part of the cap.

Psyco I learned something today. Dissected my old blue '01 cap, it has a pressure release and a vacuum break built into it. Pressure release in case of boil over and vacuum break to allow air into the expansion tank as it cools. (plus a nice little round screen for your hash pipe) The burp vent to get air out of the system is in the black plastic "cap" with a metal bale on it mounted on the expansion tank behind the blue cap.

Quotes source post: 3245051

Quote: It's all good, no worries . That's the beauty of 6speed everyone can learn something new (including or especially myself ). Bottom line is that a defective cap will either cause increased pressure on the system and you'll get a leak at a weak point (crack in tank, hose connectors etc.) or the opposite and hot coolant will start coming from the cap it self. Cheers! Sid.

I know this thread is over 6 years old, but I have the proverbial new 996 owner question. I bought a 2001 911 Carrera 2 Cabriolet in Feb with 81K on it. I made note of the smell of antifreeze in my original test drive, plus subsequent trips and in the instructions to the local Porsche dealer who did a PPI. The dealer claimed no leaks under the pressure test. Yet I have lost 2 gals of coolant in 500 miles. (1/2 oz per mile). Yet all seem to say the car is ok. Now it notice the car runs hot, with gauge showing over 180 degrees and sometimes shooting up toward the 230 degree mark especially if I sit in traffic. Yet there had been no evidence of a drip leak, just the low coolant warning light on the dash when the level fell below minimum. I've already cleaned out the debris in the radiators and pressure-washed them, so that wouldn't seem to be a factor. Yesterday, I did get a steady drip when I accidently overfilled the expansion tank and the blue cap leaked quite a bit. Haven't driven yet with the level back down where it is supposed to be. That would point to maybe a defective cap. So the question is, with theses snippets of info, is it a stuck thermostat? low coolant flow due to a broken composite impeller on the water pump (no leaks around the pump however)? Too much distilled water and not enough antifreeze? I'm starting to go insane ...

Quotes source post: 4728492

Quote: first things first... 1. When you start the car with AC on full blast, do the front fans come on? 2. Do you know if the water pump has been changed out in the last few years? 3. Was the thermostat tested? Have you thought about changing out the thermostat with a low temp version?

Thanks for your thoughts. 1. When you start the car with AC on full blast, do the front fans come on? Yes, now they do. Before I washed out the AC and coolant radiators, the left hand side fan did not come on when the AC was on. Now they both run. 2. Do you know if the water pump has been changed out in the last few years? I have the most sketchy historical service records, only what the Carfax listed, when I bought the car this past Feb. Not even the most recent owner, who traded it in, provided any documentation ... no owners manual, maintenance records, parts replacement, etc. In the Carfax report, there is no listing of the water pump and/or the thermostat ever being changed. At 81K, it is starting to look like the next thing to do 3. Was the thermostat tested? Have you thought about changing out the thermostat with a low temp version? Per #2 above, I have not tested it. If it is the original 17 year old factory thermostat, it has lived a long life but needs to be shot. I was also considering the low temp thermostat when I was considering the pump change-out. I do wonder what I'll find out about the pump vanes. If OEM was a composite impeller, I am expecting to find the vanes in iffy shape anyway. The failure scenario I am piecing together says that the pump impeller has lost some vanes and the thermostat has lost its full range of motion to fully open. Why else would it seem like the cooling system is not up to the task of keeping the engine cool, even at idle?

Quotes source post: 4728699

Quote: responses are below... When you start the car with AC on full blast, do the front fans come on? Yes, now they do. Before I washed out the AC and coolant radiators, the left hand side fan did not come on when the AC was on. Now they both run. The is one indication that you may need to replace your resistors. I would start and replace the driver side first. It's a common problem that these go bad. More than likely, when the radiators were clogged up it produced too much resistance and the fan wouldn't work at low speeds. I've had this problem. If it's not the resistor, then it may be the Stage 1 relay. But again, I would recommend replacing the resistors. Here's a video... You Tube 2. Do you know if the water pump has been changed out in the last few years?I have the most sketchy historical service records, only what the Carfax listed, when I bought the car this past Feb. Not even the most recent owner, who traded it in, provided any documentation ... no owners manual, maintenance records, parts replacement, etc. One easy test is to remove the serpentine belt and test the water pump for faulty bearings. Once the belt is removed, try spinning the hub and see if it moves smoothly with no resistance or noise. If you know that it hasn't been changed out in a long time, then you should plan to replace it. Of course, you can remove it and see if the impellers are damaged. The worst scenario is the impellers have broken off and blocked the coolant passages on the motor. Let's hope not! Unfortunately, it's another common problem with these motors. That's why Porsche recommends replacing it regularly as preventive maintenance. Avoiding it can permanently damage the motor from over heating such as cracked heads or even cracked blocks. IMHO. Here's a good video on the process... You Tube 3. Was the thermostat tested? Have you thought about changing out the thermostat with a low temp version?Per #2 above, I have not tested it. If it is the original 17 year old factory thermostat, it has lived a long life but needs to be shot. I was also considering the low temp thermostat when I was considering the pump change-out. It's a good idea to change it out with a low temp thermostat from LN engineering. Here's the link... https://lnengineering.com/products/1...e-install.html You Tube Good luck and don't ignore this problem. It will only get worse. Cheers!

Thanks. All very sound advice, and I'm compiling my parts list now, including the drive belt. I'm curious about one thing left. This coolant problem was first detected during my first test drive, and the temp gauge did NOT register a problem on those test drives (granted it was a 45degree day in February). I could definitely smell the antifreeze after every drive, noticing it when I stepped out of the car. The selling dealer (BMW) and the one who did the PPI (Porsche) both stated it was just probably from the car not being driven a lot. Seemed plausible at the time, but now it is clearly bad advice from them. Also, maybe my nose is now highly attuned to sniff it out, having had coolant leak issues on some of my prior cars, e.g., Austin Healey, Jetta, MGC, BMW 635. The smell of glycol is something I pick up quickly. Also very puzzling is there is no obvious evidence of WHERE it was coming out on the Porsche. The only time I saw anything was this past weekend with the overheating and the blue cap was bypassing coolant, which then went down its overflow tube to the ground. So with no initial evidence of overheating, but clearly there was coolant being lost, where else could the loss be occurring? Should I at this also just replace the cap? Am I possibly dealing with something more than a bad cap on the coolant expansion tank? The cooling system with the existing blue cap seems to hold pressure for several days of no driving. I can hear air escaping under pressure when I remove the cap. Is it relevant that the tank fluid level usually then rises, even overflowing? Also, I hear gurgling as I do this. Is this because air is in the system and needs to be purged? Can't believe this is so mysterious. Probably a simple root cause that I'm missing.

If the part number on the cap does not end in "04" you have the old style cap which was prone to leaking. One caveat - I read one account where someone added the new cap and the increased pressure caused his old coolant expansion tank to crack. It was likely ready to go and the new cap pushed it over the edge. If your tank has yellowed, it's probably wise to swap that out as well. With a MY 2001 with little or no maintenance history I would replace the following: Water pump (OEM with composite impeller and OEM metal gasket) Thermostat (Low temp 160f) Serpentine belt Coolant tank and cap (OEM from Germany, Cap part number ending in "04") Even if none of these items are the cause of the leakage, they are things that should be done anyway. 2 gallons in 500 miles is a lot of leakage.

Pump, thermostat (low temp) and belt are definitely on the to-do list. The expansion tank looks brand new (bright white) and the cap is the new blue one. See attached photos. No part number on it however. Says 'Germany' on it. A clone perhaps?

I would go with the genuine Porsche cap (blue, ending in 04). Someone on another forum had a problem with an aftermarket cap.

So a real Porsche part would have the part number on it? This one, although bright blue, has no part number on it.

Here is the latest Porsche cap.

At this point we can't tell if the cap is the problem, but you can eliminate one variable by putting on the proper cap.

Made the drive of 20 miles to local Porsche dealer and bought a proper cap, with part number molded in. Wasn't sure I was going to make it all the way to the dealer because the low coolant light went on just before I got there. The expansion tank was on the Max lone when I started. Interesting that the temp fell from over the right edge of the '0' in stop-and-go traffic to between the '8' and '0' on the temp gauge while driving at 60+ mph on the expressway. Drove all the way back with light still on. Will now let it cool down so that I can top it up and put on the new cap. I am eager to see how it behaves ... hopefully some improvement and proof it was only the cap leaking.

Quotes source post: 4728848

Quote: Sounds like you may have a faulty coolant level sensor. This may be the source of the leak that you smell. Good news... Those sensors are pretty cheap - $40. Bad news - You'll have to remove the coolant reservoir. (see pic)

I was hoping, given the apparent newness of the tank that I could avoid the gymnastics required to get it out. Your assessment does make sense though. If the sensor was leaking from its location at the bottom of the tak, shouldn't I be seeing evidence of the leak?

Quotes source post: 4728865

Quote: My theory is based on the fact that you're getting a "low coolant" MIL while you've confirmed the reservoir tank is completely full. You could have a extremely small leak that is dripping onto the hot exhaust which would give you the glycol cooked smell. But the leak is not large enough to create a puddle under the car while parked. Remember, the coolant will more likely to leak while running since it's under an enormous amount of pressure. While the car is parked, the pressure subsides and thus, doesn't produce a puddle. Just my theory. Seems like you're making the right steps. I'm still hoping your water pump impellers are still intact. Keep us updated! Also, the coolant expansion tanks are also prone to leaking. If you choose to replace the level sensor, I'd recommend installing an OEM coolant expansion tank to be safe. They're a PITA to install and so it's smart to save the trouble in the long run just in case the sensor wasn't where the leak was occurring.

Actually the low coolant light is not on when the tank is at or above MIN. Today, when I took off for the drive to the dwalee, the tank was at MAX and the light was not on. It was after maybe 15 miles on the highway that the light came on. However, if the seal around the sensor is leaking, that would explain the loss of so much coolant. I am wanting to keep the coolant temp from rising so much in stop-and-go traffic. That points to the pump and belt replacemnet task.

In the image of the replacement sensor, I don't see any grommet or sealing ring. Is there one that would come with the sensor?

Quotes source post: 4728908

Quote: I don't believe there is any type of rubber seal for the coolant level sensor. Now, you got me wondering how it provides a non-leaking seal under pressure. ha!

With the amount of coolant that you're losing it should be very noticeable. You can pull out the airbox and secondary air pump with not much effort. That should enable you to reach in and feel the underside of the coolant tank. It could also be a crack in a radiator or coolant hose that doesn't show up until it's under pressure. There are three small hose connection on the expansion tank. Check to see if any of those are wet. Just because there is coolant on the bottom of the tank doesn't mean it began there. One other thing to consider. You said the tank looks new. Some people have reported problems with aftermarket tanks right out of the box.

Like we say about the internet, "it's magic!!"

BTW, that last post of mine was directed at 'b3freak's previous comment about how the coolant level sensor is sealed to the expansion tank. To 'wyovino', I have felt from the very beginning that the amount of coolant loss was just too big to not be detected somehow, somewhere. I will probably be replacing the pump, thermostat and belt in mid August, when I'm back from some travels. At that time, I will do a more thorough manual inspection of the coolant tank. And maybe a deeper inspect of the rest of the coolant hoses throughout.

Btw - Here is the coolant level sensor. There is no o-ring or washer, so you're right - it is magic. Notice the crack in mine. Unfortunately I broke it when I installed my new tank and had the privilege of doing it all over again.

So how on earth does it hold pressure?

Quotes source post: 4728983

Quote: German engineering.

And I have a bridge I'd like to sell you ....

Quotes source post: 4728983

Quote: That's really a good question, but we must realize that the coolant level sensor is located at the bottom of the reservoir. Higher pressure resides at the top. Imagine boiling water in a sauce pan... where is the energy released? Get my drift? However, I'm still baffled at how Porsche achieve a proper seal with plastic on plastic. Even at very low pressure, seems like coolant would still find it's way out.

I don't want to sound like a physics professor, but if you have 15 psi at the top of a container of liquid, it also has to be 15 psi at the bottom. Any difference in pressure would cause liquid to move from the higher pressure to the lower pressure area, causing them to equal. That's equilibrium. Your more important point is how in God's name the plastic on plastic seals at all. Mystery ... And one other question tp ponder ... do new expansion tanks come with the sender already installed?

Quotes source post: 4729050

Quote: No, the sensor does not come with the tank. When you install the sensor, it twists and locks rather firmly.

Any gasket cement or o-ring involved?

Quotes source post: 4729050

Quote: I must have fallen asleep in science class. haha I was thinking the vaporized state (at the top of a container) would exhibit increased pressure greater than the expanding liquid state as temps increase. Oh well.

Quotes source post: 4729055

Quote: I think you were right the first time. I had a flat tire the other day but it was only flat on the bottom.

Quotes source post: 4729071

Quote: bwhahahahaha!!!!! Yea, I better stop while I'm ahead! Thx Bill.

Seems the non-Porsche brand expansion tank cap was a major culprit (but probably not the only one). Put a proper Porsche one on yesterday and drove maybe 20 miles just now. Can't say I noticed any leaks or as much of a glycol smell. Temp stayed between 8 and 0 on the gauge while on the highway, so no real change there. The temp needle did climb above the 0 just as I got home, so maybe those other tasks (pump, thermistat, belt) will fix the rest . of the issue. I will also keep an eye on that coolant level sensor under the expansion tank for leaks. I did notice that both front fans were running well, along with the one over the engine bay.