996 Coolant disapearing and reappearing

if the temperature is normal, can we have compression gas in cooling system. What else could it be. What tests should be done before removing motors and checking for cracks in cylinder head or worth. Bought a 996 recently on Ebay that has been a real nightmare. Drove it 1 day from Las Vegas to Monterrey. Smell of coolant. Temperature high around 200+, but no lights warning. Oil pressure OK, but less than 1 at iddle in traffic. Next day a lot of steam coming out of the motor bay. Stopped the car on the highway. Had it towed. After close to $4000 bills (spark plugs, water pump...), the car was shipped to Canada. The car was supposed to be OK. Upon reception, car smoked like crazy (same as pictures on you tube of intermix). Oil separator changed (around $1500). Left the Porsche repair shops, but coolant hose broke within 10 mn. ($500 to repair). All that to be told that compression gas inside the cooling system, coolant hose expansion and that I will need a new motor or at best cylinder heads. Yesterday, I decided to drive the car 3 hours (first time since California). Temperature between the 8 and the 0 of the 180, but 1 inch of coolant disappear from coolant expansion tank. All coolant went back in the reservoir overnight. Is it possible that more coolant is in the cooling system, especially in the block when hot and return to the expansion tank when the car is not running? I would have thought the opposite. Thanks for your help before I spend another $15000.

Would be useful to know the year of the car, model, mileage, trans. type.

Porsche 996 cabriolet 2001 with 106,000 miles.

tiptronic transmission

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These engines have been known to crack a head. Depending upon where the crack is this can result in "compression gas inside cooling system". But I take it no CEL thus no misfire (or any other) error codes? That doesn't really read like a cracked head or a severely compromised engine cooling system. If the coolant level drops then returns to normal this is kind of weird but if the cooling system is not properly filled with coolant, if there are air pockets, strange things can happen. One has to I guess prepare for the worst and hope for the best. I guess what I'd do would be to collect a good oil sample and have the oil analyzed for presence of (among other things) anti-freeze compounds. If these turn up in the oil then this is a pretty good sign there's a real problem. At the same time I'd look for signs of oil in the coolant. Dark globules of oil in the coolant in the tank is one place to look. You are going to probably have to enlist the help/expertise of a reputable and experienced Porsche tech. When the water pump was replaced, was the old water pump intact? Did it have all its impellers? Are you smelling antifreeze odor from the car when hot? Sniff the engine bay with the engine compartment lid open but give a sniff around the front of the car, around the radiators. While I am reluctant to advise you to drive the car it is up to you (and you probably should consult with a tech in your area first). If you can drive the car then drive the car and with the A/C off get the engine and everything up to temperature. Then back at your house raise RPMs to say 1200 and hold until you or a helper hears the radiator fans come on. Be sure both are running and blowing the same amount of hot air, too. Then shut off the engine. The heat load will raise the coolant temperature and pressure and if there is a weak hose, coolant tank, cap, radiator, whatever, the odds are it will make itself known with a leak. Careful. The leak can be a gusher and it will spew hot coolant.

There are no coolant in the oil. No oil in the coolant. Thanks for your response. If the temperature is OK, can I still have an engine failure? I used to smell coolant. I think i still do a little bit just behind the driver's seat. However with all the coolant that may have dropped on the motor, i am not sure of it or if it could be a small leak. Re the air pocket, i think it could be possible as on a 996 it is difficult to remove them. Because of the hose leak, i had to pour 4 gallons. Although the Porsche mechanic most likely had to remove it to change the hose, may be they did not bleed the system properly. What test can we do to check if the head gaskets are blown?

If the air pocket is not too large you can "burp" the system yourself. With the engine cold. Remove the blue coolant cap (part number should end in 04, if not get a new one) and fill the reservoir to about 1/2 way between the min-max lines. Snap the metal bale up (on the black cap) drive with varying RPM until the car is fully warm ~180. Park the car and let it cool, overnight is best. Make sure that it is still at least 1/2 full or more refill to 1/2 if needed. Snap the cap down and drive it until it is warm again. Let it cool and check the coolant level, refill to 1/2 way again if needed. If you fill the coolant to MAX when it is cold it will push coolant out as it expands when it gets hot. If the coolant does not settle at just above the min line when cold or right at the MAX when hot you can "burp" it again.

Water pump was touching the case but no broken part. No metal in the oil. Re the metal pin on the expansion tank. Something looks strange. I can put it up, however, it does not seem to do anything as the metal seems loose, there is no resistance nor pressure to bring it up. I should think it should lift something (the black square that is attached to it) . When I put the pin down, it just flop down. There is no feeling of either closing or opening something. It just look like a pin attached on the expansion tank. is this normal? That garage in Canada did install that new expansion tank ( I do not know why) and the oil separator. I put the car on a hill ( motor down) fill up the extension tank. Let the motor run for 15mn. Top the expansion tank up on a flat surface, then drove the car for 20 mn with pin up. Parked it top it up again. That pin seems loose. How it should feel?

After a drive and the car stabilizing at operating temp, the burp valve is forced up and open. The hoop will seem loose and floppy, this is normal. When it's warm can you push the black square post the loop is attached to down a few mm and feel resistance?

Thanks I will try tomorrow. Does that mean that all the time, the burp valve was up and opened and that if there was combustion gas in the coolant, the temperature will not go past 180. In that case, could I have still a cracked head?

What about just bleeding the cooling system completely and then refilling it from scratch. With all the stuff going on, I would want to make sure the system has been properly filled with the right amount of fluids.

I think it is a good idea.

Constant coolant smell might also be a crack in the coolant tank. Look for dry residue under the area of the tank.

It's not a good idea. Park the car nose down and jack it up until the bottom of the front bumper almost touches the ground. Then open the talk and start the engine. Turn the heat up and let it run for a while. Once the coolant start to drop, slowly top it up. At some point the coolant will stabilize. Close the tank and open the pop off valve. Lower the car and go for a drive. After the drive have a look at the tank. If it needs coolant, add some, otherwise close the pop off valve. I call it a pop off valve but I'm sure the Porsche name is something else.

The bail opens a vacuum break it does not open the tank/system to atmosphere while it is hot. The bail opens a vacuum break it does not open the tank/system to atmosphere while it is hot. The bail opens a vacuum break it does not open the tank/system to atmosphere while it is hot. It breaks the vacuum to allow air to escape to the tank as the system cools. The blue cap pressure valve allows air and coolant to escape as the system warms up creating pressure. Before you pull the engine apart for air in the system why not bleed it correctly as Imo00 and others have suggested? EDIT: Post 8 reads like you did. How is the level now? It reads like you had the engine down hill? Turn the car around so the engine is uphill. You want the engine and tank higher then the rest of the car. Use one of these: http://www.tooltopia.com/uview-55000...Fajm7AodokcAXQ

I really hope this is a lol moment. But how can a shop do thousands of dollars worth of work and not go over everything? Any repairs should be followed up by a thorough test drive by the mechanic. Really surprised these things weren't caught by mechanic. Good luck

I meant the car down hill and the motor in the back i.e.. I pushed down the burped valve this owning and went for a drive. The burped valve popped up by itself. The temperature is still OK. Still a smell of coolant. The level has not changed from last night. I was planning to add more coolant later on today and park the car on a slope again and with the burp valve up let the motor run (do what is suggested) and then go for a drive. However, now my engine light just came up. I do not know if it is related. I will need to have it check. I have a bad feeling.

Just an update. I have been driving the car for the last few days around town. No loss of coolant. Temperature still between the 8 and the 0 of the 180. However, can still smell coolant near back left side of the car. But coolant level when I stop is below the minimum. Did not drive the car one day. Next day, level below minimum. I opened the blue lid, I hear pressure and then the level goes up right away to the maximum level. 1) Should we hear a pressure hiss sound when we open the coolant lid after one day? 2) Can hose expand? 3) can it still be air in the cooling system 4) let's face it cylinder head or sleeves?

2000 & 2001 heads crack very easily, have the coolant system pressure tested. Head gaskets never fail.

+1 on pressure test. Stant has a good tester for about $70. Does your coolant CAP part number end with .4 (the latest)? That black bleeder valve will pop up by itself whenever the reservoir pressure is around 14PSIG or higher. What error codes are there now that you have a CEL?

Black bleeder valve popped up again. Temperature still between the 8 and o when I drove the car RPM around 2000. Will it make a difference if I increase the RPM I do not have a cell.

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Black bleeder value popping up is normal and it's not a problem. Two posts above you said your check engine light is ON? Are you able to retrieve any error codes?

I'm gonna laugh if this ends up being an overly paranoid moment much to do about nothing. I hope I'm wrong.

The code was for a O2 sensor. Was told by garage (porsche mechanic in Canada) that it has nothing to do with coolant system. Cost of the potential repair to replace sensor around cdn$1000. Told them I wanted to resolve my coolant problem. I asked them to reset. I have driven the car two days, the light has not come back. However, my problem still remain. Slight coolant odor when I drive. Pressurized tank (hiss sound) the next morning when I open the blue lid. Was told by the other Porsche mechanic that there is a lot of coolant in the system (gallons) which explains that the temperature can remain at 180, but that the motor is toast. Does that make sense? Can i still simply have an air bubble in the system? Or I need to face reality. Can someone answer my three questions above. Flat six post thinks it is the cylinder heads. I am told by both mechanics in Canada to replace the motor. The car is 106000 miles. I am thinking to do an engine rebuilt ($7500) instead as buying an unknown motor could be more problems. Is there a Porsche shop around Bellingham Washington that could help me to make my decision. If not i will ship the car to California for an engine rebuilt. (Around $7500).

Coolant odor at the back drivers side when hot is usually a cracked coolant tank. It will squirt some out when hot, does your drivers side exhaust tip have dried coolant on it? Have you checked your oil lately? Has the level gone up or down?

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The odor of anti-freeze is almost always from a leak. "Almost" in that I smelled this after having the radiators replaced in my Turbo and the smell was from some coolant that got spilled when the tech added some to the tank after the radiator replacement. I finally got rid of the smell after putting up with it on a 2K mile drive back home by flushing the coolant tank area with 2 buckets of hot water. (The engine was pretty cool.) The tank can develop a bit of a low pressure. I would not concern myself with that. Unless you tell me the coolant tank was replaced my WAG is the tank is leaking. I smelled a faint odor of anti-freeze for a long time with no real sign of a leak that eventually proved to be a coolant tank. A hot pressure "test" I did allowed the tank leak to make itself known in a dramatic way. The system has a lot of coolant. This fact is immaterial in what the tech says. An engine can suffer from overheating while the coolant temp gage remains rather stable. One scenario is a leak prevents the system from building pressure. It is the pressure that prevents the coolant from boiling. At the hottest spots the coolant can flash to steam and this steam can form pockets of steam that prevent the coolant from making contact with the hot surface. Localized overheating and possibly severe engine damage can result and yet the coolant temp gage needle doesn't register any real increase in temperature. Another scenario has the coolant flow interrupted. This can be from a failed water pump impeller or a failed T-stat or the system just doesn't have any coolant in it. With no coolant to absorb the heat and flow past the sensor the coolant temp gage can remain unchanged, low even, while the engine runs and heats up to the point the engine suffers damage. Based on what you have posted I do not think the engine is toast. Absent any scary noises, low oil pressure light/warning, etc., the engine I believe is fine. I suspect there is a coolant leak and the tank seems the most likely source. A good mechanic should be able to diagnose a coolant leak without much difficultly. Sorry, but I have no knowledge of any Porsche shops in Bellingham Wash.

Thank you for your response. In California, the Porsche mechanic replaced the water pump, spark plug, coolant. He tested the car 70 miles. Apparently the car was working fine. When I picked up the car in Bellingham (it was towed), it was smoking ( like in some of the You Tube video), but we only let it run for 1 mn. The first Porsche mechanic in Canada replaced the AOS and the coolant tank (was told it was fixed). Picked up the car, but then within 10 miles, 4 gallon of coolant disappeared. Returned car to first mechanic. Was told me the motor was toast (coolant in the exhaust). Towed the car to a second known Porsche mechanic. They replaced front radiator hose, refill coolant, checked for leak run engine and bleed air, but he told me that exhaust gasses are super-pressurizing cooling system and suspect major motor repair work or replacement. (however, no coolant in exhaust) I drove the car the next day and have been driving a few miles almost every day and trying to burp the coolant in case. (I start my day on a hill trying to burp any air from the coolant reservoir) Many people on this site keep thinking like me. The motor run nice, start no problem, run smooth. But I keep smelling coolant on the back left of car. and, the coolant tank pressure remains overnight. When I drive there is no increase in temperature past the 0 of 180. No loss of coolant, but level below minimum when I drive. Also oil pressure just below 1 after 30 mn drive at idle (start the day at 5, pressure normal when I accelerate). Level going up to normal level after I open the lid of the coolant reservoir the next day (after a hiss sound).. I like the idea to throw water from a bucket to check if it could remove smell. I think these are my options: 1) if smell =a) leak b) coolant around motor outside reservoir 2) if pressure remains in the coolant tank overnight = a) air pocket, b) bad tank c)broken hose d) cylinder heads and/or cylinder sleeves. Note: re. the engine light mentioned in previous post: The sensor was P1130 oxygen adaptation, idle range 2 - Above limit Suspect mass air Flow metre is starting to fail. As mentioned so far the engine light has not come back yet. If it is bad tank, could it damage the motor or just keep pressure in the tank and then leak coolant? Now, I am not a mechanic, but I would think that a simple pressure test should eliminate all problems other than 2 d) Am I right?

You mentioned you had coolant coming out from the exhaust? Did you see if it's sprayed out from the inside the exhaust or the coolant just dripped onto the exhaust? Did you check if there's coolant in your engine oil (froth) or oil in your coolant (milkshake)?

I can only begin to wonder the amount of frustration and money this will end up causing. Good luck! Sorry for not providing and further help than what has been discussed.

I would think that if the head was cracked and pressurizing the system, that pressure would be reduced very quickly once the car was off and then the engine cooling down, it would become a wick to the coolant. So when I hear there is pressure that remains in the system over night, that doesn't seem like a head crack/leak. I would think it would totally come to atmospheric pressure over night through that crack. This is just $0.02 as I am just thinking out loud, have not been around these cars long.

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I think you need to tow (flat bed) the car to a qualified shop in your area and go over what has been going on. If the problem is a simple coolant leak a pressure test most of the time finds the leak. In this case the leak might not be so simple. It might be a crack or something that is allowing combustion chamber gases into the cooling system. Let the tech advise you but I would think checking the oil for any presence of water/anti-freeze would be a step. It might be of value to send a properly obtained sample out for analysis which among other things looks for anti-freeze compounds on the oil. Also, the water content is checked. Plugs should be pulled and they should all look the same. Often if any coolant is getting into the engine though a cylinder the plug from that cylinder is clean. But a particularly nasty looking plug is also a sign something's wrong with that cylinder. No misfires though and no CEL so I suspect the plugs will prove to be 'ok'. But let the tech tell you this. As I think Jake R. mentioned water in the exhaust is also a smoking gun (paraphrasing what he said). The car is not of any use to you the way it is now. I do not think you can do anything to address the behavior. While the problem may not be serious you risk more serious engine trouble, damage even, if the cooling system is compromised. So spend some time and research and find a good Porsche repair shop in your area. One that comes highly recommended by other Porsche owners and recently too. Often a good shop can have good techs for a while then the techs leave for greener pastures and the shop is resting on the laurels earned by techs no longer there.

Not sure if this has been suggested http://www.autozone.com/loan-a-tools/block-tester it tests for exhaust gasses in the coolant. May be worth a try

another thread that died. it should be a rule to finish a thread.

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I nominate this as the best post EVER on this Technical Forum !!

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lmao. It just boggles my mind. I go down a rabbit hole and then pull my hair out.

Damn, that was 10 minutes wasted.

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I hope you are kidding because so was I. If you are being an *** then, may god have mercy on your soul. 🙄