Advice Needed - Oil in Coolant 1999 996 3.4

Long time consumer, first time poster. Recently acquired a 1999 911 Carrera with 80K miles (History unknown) Symptoms: * Oil in the coolant. . * No apparent coolant in the oil. . * No excessive white smoke. . * No ODBC error codes Test conducted along with results: Compression Test - Less than 8% variance between highest and lowest cylinders. Leak Down Test - Less than 10 % leakage on any cylinder. First, please forgive my ignorance, but I am a weekend enthusiast at best, but enjoy doing as much work myself and learning along the way. Any guidance/direction at this point would be greatly appreciated. My questions are as follows: Do the successful compression and leak down tests suggest a non-internal issue such as an AOS or the Oil Cooler? Or is this still likely a head, or head gasket issue? Prior to taking this in for professional diagnosis, would anyone have any suggested next steps? WHILE I am willing to do so, I would prefer to not drop the engine if not necessary. Thanks in advance for any suggestions.

My condolences, however, this intermix issue is not fatal and can be resolved albeit with some expenditure of time and $. First, it is NEVER the head gasket, these cars use a triple layer steel head gasket. Second, the oil cooler and the AOS can be tested although doing so with the engine in the vehicle would be quite difficult as they are both located in the upper rear of a super tight engine compartment. Third, the compression/leak down test results would only be relevant if your intermix issue was due to a cracked cylinder or combustion chamber. As your numbers are good and you have no excessive white smoke, I would suggest we can discount those two possibilities. If you are serious about repairing the vehicle, resign yourself to pulling the engine/transmission. Its removed as a unit from underneath by raising the car, Its really not that bad, I did it by myself but was very careful. Also, while you have the engine/transmission out you can attend to any other maintenance such as changing the tranny fluid, changing the clutch/pressure plate/throw out bearing, servicing the fuel injectors and or vacuum lines, or changing your coolant reservoir tank (highly recommended), etc. The oil cooler can be pressure tested which I did to mine, not sure how to test the AOS but I'm pretty sure you can find the info on this platform. I replaced both with new as they had 70k miles on them, and my issue was indeed a cracked head which I identified with a penetrant dye test. The head was sent to Hoffman Automotive Machine in Atlanta GA for welding/machining (they are the acknowledged masters). You mentioned having oil in the coolant but no coolant in the oil which means oil is getting into you cooling system while the engine is running as the oil pressure is higher than the coolant pressure during engine operation. When the engine is turned off, the coolant pressure is higher than the oil pressure. BTW, with the engine/transmission out, you will need to clean out your cooling system, including your heater core and both front radiators, to eliminate the oil as it will ruin your rubber hoses. Plenty of info on this platform and on-line regarding how to accomplish that. This process is a series of steps that you'll accomplish one at a a time until all the steps are completed. Just focus on the current step, and then move on to the next because if you fixate on the entire endeavor it will seem quite daunting. Several members of this platform have recovered from this issue and are available for advice and guidance. My experience was positive in that I learned a great deal about the car, did all the "while I'm in there" maintenance, so the result was a well sorted car that I can enjoy. The primary lesson I learned was to stay on top of the cooling system as these engines are very sensitive to overheating. Any questions, just ask!

Quotes source post: 17217908

Does the engine have a new (or newer) water pump by chance?

Quotes source post: 17220642

I think the reason Charles is asking is to probe the possibility of a pre-Dchunk cylinder crack. Since you have no history on the car, try to see if the water pump gasket extends beyond the pump toward the passenger side. If it has been cut free, the pump has likely been replaced.

Quotes source post: 17220796

If it had a previous pump fail, bits of the impeller likely made their way to the heads and that's the reason why they cracked and are causing oil to get into the coolant.

Dear Friends, I don't want to hijack our fellow member "JIM R" but I have the exactly same problem with my car ( an unknown history 2000 996 convertible with 90K miles ) and I don't want to create a new thread with the same issue - I did not make any leak/compression test - The oil cooler was pressure tested and its ok - The AOS was not tested - There is a lot of oil in the water reservoir, but the oil on the deep stick is very, very clean - I don't know if the WP was replace any time, don't have the car here with me now, to see if the gasket was cutted - No matter what I'll put the engine/transmission out ( to try to fix this issue + IMS + Clutch +WP + OAS + Coolant Hoses + Water reservoir + Vacuum lines?! + Oil pressure sensors + waterever you guys tell me its a good time to change) But my questions are: 1-) Let's assume this whole problem was the OAS (not likely) could a faulty OAS cause that much oil in the coolant system? and if yes, how can I double check this info before disassemble the heads ( which is going to be another can o worms) 2-) Now let's assume the head is cracked, how do I check for this? Is the only way to check this is but tearing down the whole thing? 3-) Once I have the heads out, how do I check if they are cracked? Sent to a machine shop or use some type of dye? 4-) Most of people say that its the head 1-3, but then again, what if it's both or bank 4-6? So my question is: Do I remove both, no matter what? Do I send both to the machine shop so the head that is not bad could be checked and the valves guides and seat cleaned / refitted / fixed / improved, so I can have both heads in a OK shape? 5-) Once I remove the heads, how can I check if the block/cylinders lines are not cracked as well? Is there some kind of dye to do this job or again, I'll have to ship the whole assembly to a machine shop to be checked? 6-) I heard that there are 2 kind of bolts that holds the heads on the block, where one is a elastic one the other one it's not? Is that true? If yes how can I know which one my engine use? Thank you all for the help and I hope some of those answer could help out JIM R as well

Quotes source post: 17254699

1-) Let's assume this whole problem was the OAS (not likely) could a faulty OAS cause that much oil in the coolant system? and if yes, how can I double check this info before disassemble the heads ( which is going to be another can o worms) No, the AOS is not the common cause of intermix on M9X Porsche engines. However, a faulty AOS can lead to hydrolock if not replaced. 2-) Now let's assume the head is cracked, how do I check for this? Is the only way to check this is but tearing down the whole thing? Most intermix problems are because of a crack in the heads on these cars. Remove both heads, send them to Len Hoffman for testing and rebuilding. They will pressure test to locate the crack. 3-) Once I have the heads out, how do I check if they are cracked? Sent to a machine shop or use some type of dye? Again, the must be pressure tested. This is like looking for a hole in a tire. Soapy water is used while pressure is added. The bubbles will show where the crack has formed. 4-) Most of people say that its the head 1-3, but then again, what if it's both or bank 4-6? So my question is: Do I remove both, no matter what? Do BOTH banks of heads. While the heads are removed, change out the chain guide pads too. Do I send both to the machine shop so the head that is not bad could be checked and the valves guides and seat cleaned / refitted / fixed / improved, so I can have both heads in a OK shape? Yes, send both heads to be rebuilt, IMHO. 5-) Once I remove the heads, how can I check if the block/cylinders lines are not cracked as well? Is there some kind of dye to do this job or again, I'll have to ship the whole assembly to a machine shop to be checked? The cylinders and block should be inspected by trained professionals as well. Maybe you should just plan to have the engine fully rebuilt? 6-) I heard that there are 2 kind of bolts that holds the heads on the block, where one is a elastic one the other one it's not? Is that true? If yes how can I know which one my engine use? The head bolts are high torque-to-yield type fasteners that should never be reused. Of course there are other fasteners that bolt the lifter carrier and crankshaft bearings in place, but there is only one type of head bolts on these engines. They are very long and extend to the main crankshaft carrier.

Quotes source posts: 17254699, 17255332

If the head bolts are T50 Torx 234mm long they MUST be replaced If the head bolts are T55 Torx 230mm long they can be re-used Some early M96 engines up to 1999 had "Torque-to-Yield" head bolts that MUST be replaced, later head bolts were NOT TTY and can be re-used if desired.(saves $250) per Porsche item 20

Dear b3freak, Thank you so much for your help and expertise! I'll follow your advices to the letter When I remove the head bolt and if I find the T50 TTY, then its easy, I will replace If I found the T55, then I'll see how the checking account looks like that particular day... My first instinct is to change for new one even if they are the T55, you know, since I'm already there kinda of deal, but then again, if on the Porsche manual say i can reuse them, why should I?! I don't know, let's see... Again, thank you so much for the input

Dear Porschetech3, I would like to thank you for your input as well! As I said on the last post Ill remove the bolts, see what I have and decide from there Also if it's not to much for ask, I wonder if you have the torque specs for those head bolts and the pattern to follow Thank you once more Ricardo

Quotes source post: 17256195

Nah don't have them handy, and don't feel like looking it up for you. Its something like low torque + 90* + 90*.. You need to buy Jakes torque spec book, you will need it on other stuff.. The money you can save from the head bolts would buy the book and have plenty left toward other stuff,( like UAOS. ).. If you use the search function on here and search, you can find the full 996 service manual, it has all torque specs in it but they are scattered throughout sections, so searching is necessary. jakes spec book is much easier ..