996 Loosing coolant - no leak

Hi, As I think is the case for many 996 owners, i'm somehow convinced my engine is shot The car is a beautiful 2003 C4s with 137k kms (85k miles). The previous owner has documentation of an engine rebuild at 119k kms (73k miles). When I got the car, a few things were wrong, it was smoking like crazy and it was throwing a 2 secondary air system failure code + 1 catalytic converter efficiency below threshold code. There was a big vaccum and the engine ran really rough with the oil cap off. These problems were all fixed by my (trusted) indie, who replaced the AOS, deleted the cats and installed an OTS tune to remove the cat codes. Although this indie is trusted, something happened to the car over there (that he admitted) : The Porsche specialist did the repairs and everything, and another mechanic drained the oil. The oil wasn't completely drained and it ended up being overfilled by 1.25 quarts. The car smoked smoked smoked while overfilled, and it calmed down after a the extra oil was drained, but still smokes a bit on some startups and will sometimes continue to smoke for 2-3 minutes (lightly). The weather here in Canada is cold and humid at this time of the year, so might just be normal. There is what I reckon is a oil smell (not coolant). There is clear fluid in the tailpipe a little bit bur nothing shoots out. The issue is that some coolant is disappearing . My garage floor is white (cream), a leak would be obvious. Bone dry. Except sometimes water from the middle of the car, which I assume is condensation from the AC. I had the coolant cap ending in 01, changed it for an 04 and issue persists. I cleaned up around it and no coolant seems to be pooling up there. No traces of coolant underneath the tank either. After running the car (and letting it cooldown, but not completely) I came to add coolant. I unscrewed the cap and a lot of hissing occurred and the coolant level went up a bit. like if it was under a lot of pressure and expanded. About a quarter of a gallon was necessary to top it off. I ordered a test kit from amazon to see if there is exhaust gas in my coolant tank (that is yet to come). Apart from the idle being a little rough (passenger seat shaking a little bit) and sometimes taking a longer time to crank there is no other issues with the car. Coolant is pink. Oil is clear on the dipstick, usual 996 mayo on the filler cap. Similar to what is described as normal on other posts. I heard my issue could be either a cracked head, cracked cylinder wall or head gasket. I heard head gasket is unlikely but with the recent rebuild I guess it is now a possibility. My questions are: - Are there other signs I should look for? - If its a cylinder head crack, i heard some guy in georgia can re-weld it? - If it's a cracked cyl liner or D-chunk, is the core still valuable, and are most of the parts re-usable? how much are these rebuilds? - If the temps are fine, can I ruin anything by driving the car? My indie can't see it for another month. Thank you all : )

Have you pressure tested the cooling system? Has the coolant reservoir been replaced? If the coolant reservoir is a yellow color it is old and probably brittle. This is a known problem with the 996. Coolant tanks age and develop small cracks that will leak hot coolant (which evaporates off) and doesn’t necessarily leave a puddle on the floor. Look around the underside of the car near the coolant tank for evidence of pink residue from coolant. If you replace the coolant tank use only a Genuine Porsche tank. Most aftermarket tanks fail in a short period of time and it is not worth the money you save on the part if you have to do the job twice. Good luck with it Mark

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I second everything 168Sierra has said. This is the likely scenario.

Been chasing a coolant leak on my other car for months (not a 996). Finally, went to AutoZone and picked up a bottle of Coolant UV dye, added to the tank and drove a couple of days. Also picked up a cheap UV flashlight. Found the leak after 2 days! Works great for chasing down a not so obvious coolant leak.

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The only pressure ''Test" I have done was to make sure it is still ''hissing'' after I remove the cap when the car was left alone overnight. I am booked with my indie on may 31st to have the coolant leak investigated so I assume they will run these tests. However there is an update: I got the block tester fluid to see if there are combustion gas in my coolant, and while it doesn't go full yellow, it definitely turns green. Could that point towards a cracked head or headgasket?

More likely a cracked head, the head gaskets are metal and rarely ever fail. Cracked head could be result of localized overheating due to failed water pump. The water pump fails by pieces of the impeller breaking off and get lodged in the small coolant passages in the head causing localized overheating. This is why it is recommended to replace water pumps every 3-5 years and to only use genuine Porsche water pumps. Check for coolant in the oil and oil in the coolant. If you have a cracked head it can be repaired. Send the head to Hoffman Machine near Atlanta. They are the best on 996 heads. Mark

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Thank you so much Mark you've been really helpful. No intermix so far, which is good I guess. The reason I was thinking maybe head gasket is that because it's a rebuilt engine it could be an aftermarket gasket or not properly installed, and also I thought the heads on the 3.6 were unlikely to be cracked? I was worried about a cracked liner or D-Chunk, would that have different symptoms ? And should I park the car until my indie can see it?

How much coolant are you losing? Pull the plugs and inspect them. That may give you an indication of a which cylinder may have a problem. Depending on how much coolant you are losing I would be very careful about driving it until you get a n inspection of the cylinders. It could also be a small pinhole in a hose. A Pressure test of the cooling system would be the best way to check it out. That is what I would start with Mark

I was losing coolant over the course of a couple of months with no puddles or visible leaks that I could see. I finally put some pressure on the system and found a leak at the hose the comes off the bottom of the coolant tank. Once I pulled it off I could see some white staining on the bottom side of it but other than that, there was nothing. https://www.fcpeuro.com/products/por...he-99610685103

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Blown head gasket is not likely. 3.6 heads can definitely crack. Often from water pump impellor debris, but also from cooling issues.

My 996.2 had a minimal leak that I couldn't find. I would lose 4 or 5 ounces of coolant every season (couple thousand km's). On a hot (90degree) day, wife and I went to a Porsche event. We were in an area of town we usually don't make it out, after the event, decided to go for a drive to go see Drake's house and drove somewhat aggressive. Stopped for coffee, came out to find a pool of coolant under left rear. Coolant tank. Replaced it, have never seen coolant loss again. Never saw any coolant on the ground before it pooched.

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Had the same issue when I bought my car with my coolant being low and couldn't figure out where it was coming from. The tank decided to give me a clue. its coming from one of the 3 hoses on the bottom of the tank.

Update : Took it to the shop that did the rebuild, and after discussing a few minutes and testing the coolant, they think it's a cracked head. They happen to have 3.6 heads in stock, so they can help me with the issue. They don't have time to do the work right now, but in a few weeks they will. They want to have it overnight before to scope the block and see if the coolant is pooling in the cylinders. They told me it's safe to drive as it's likely a very minor leak but I think i'm not going to take any chances.