Head Gasket Woes? Or Worse?

Hi all Probably best to explain this chronologically. It may go around the houses but here goes. A few days ago, my 996.1 failed to start. It was turning over but just not firing. I assumed it was flooded due to many attempts so I stuck a booster on the battery, floored the accelerator and hey presto - the car started. I then had a large amount of dark exhaust fumes from the near side exhaust only. Ok, I thought. Maybe I just need to run that off a bit. This worked but not perfectly and I then suspected hearing an occasional misfire. A visit to my good friend and mechanic resulted in a diagnosis of a misfire on cylinder 6. I replaced the single coil pack (the old one came out in two parts ) and felt smug that I had sorted things. But there remained an occasional misfire on startup and on idle. I took her for a spin and after 30 mins or so, noticed that the red coolant light was flashing slowly, indicating low levels. Sure enough, it was low. I topped it up but the next day, after 30 mins driving I had lost about 1.5litres. I've looked for a coolant leak whilst parked. It doesn't seem to be losing anything externally either when under pressure or at rest. So I'm now inclined towards a head gasket leak. It would explain the coolant loss and the misfire (I think?). I'll discuss this with my mechanic friend over a pint or two this weekend, but does anyone have any thoughts? :?: :sad:

Any sign of water in the oil?

Ditto - 996's tend to have a little bit of "mayonnaise" in the filling neck during colder months... but with that amount of coolant loss, surely even the oil on the dipstick would look milky? (you mention 996.1 - so not sure if your car is of an age to have both the dash and physical dipstick? my '98 does...)

Or oil in the water!!

No evidence of water in the oil. There is the usual milky mayonnaise around the oil filler neck, but nothing on the dipstick.

Or lime/scale all around the coolant pressure cap? - there was a TSB/recall and revision of the earlier caps - replacement has a much beefier internal "seal" - unless you're "pressurising" the coolant system when topping it up (prob completely wrong term etc) the driveway approach is to raise the rear of the car slightly and run it up to temperature to "burp" the system... big capacity system with a lot of twists and different levels....

Take all your plugs out and have a look at them.

Unusual for head gaskets to fail, but is possible. Worst case it could be cracked head. The water loss will eventually find its way in to the sump so levels will increase. M96 engine is very good at masking these issues early on. It is repairable as I've done it. I'll post a photo later of a cracked head. Could be oil cooler on top of engine, if lucky. It would require an engine drop to remove and test. The header tank is known to crack, but would expect to see coolant loss externally. As a note, the misfire is probably coil pack, If one is gone likely others are due to fail. You may experience poor starting if water is finding its way in to one of the cylinders - you could check spark plugs after a good run and when cold for any moisture on bank 1.

First off .. i'm assuming your mechanic put a tester on the car and it had a fault code for no.6 cyl misfire . A single cylinder even if not working won't cause a car to not start .. a general fueling problem will however . Dark .. or shall we say black smoke from a tailpipe indicates a very rich mixture on that side .. coolant and you will get white smoke .. a very bright white smoke to be fair . Black smoke after cranking for a while as you have described is several cylinders having the wrong mixture or over fueling .. it's pretty normal to get dark smoke in this situation due to the amount of unburnt fuel which finally starts and burns off . I'm in the agreement with both the above posts .. you look at the spark plugs first .. if all black and sooty then its a fueling issue and we lean towards fuel pump , maf .. possibly temp sensor and so on . if a single plug is clean . maybe pinkish or just generally different from the others then a picture would help . Coolant in a single cyl .. thats bad .. very bad .. it won't take much for it to hydraulic lock .. this is what we call D chunk .. it splits the liner and an engine rebuild follows . If you seriously think its that and not two separate unrelated faults then you get the car recovered to a garage .. you dont drive it . I can't see the car and am working from a description .. so i dont think its coolant / head gasket but you don't drive the car if you think it is .. better to be wrong and pay for recovery than risk a rebuild . if i was going to test it then bore scope after being left overnight .. If diy then i would buy a cheap pressure testing kit for the coolant system .. remove all the plugs , pressurise it over night then in the morning look for coolant dripping out of a plug hole . I would also be taking a picture of the plugs and posting here I don't wish to scare monger .. i've only once before said get a car recovered in 7800 posts but if you think its coolant in a cyl then that's my recommendation .

Morning all First off - many many thanks for the responses. It all helps to confirm thoughts and add new ones. Yes - the cylinder 6 misfire was identified via a fault reader and I'm completely on the same page regarding the over rich fuel and black exhaust fumes. It all makes sense. What doesn't tie up is the coolant loss and, unfortunately, I'm suspecting the worst here. This morning, I started her up just to move her to a convenient location to get to the spark plugs. No black smoke now but plumes of white primarily from near side exhaust and a lesser amount from the off side. I'm going to tow her to a nearby workshop where I can get her on a ramp.

Ok .. yeah don't start the car again .. it does sound like a head gasket. No.6 cyl exhaust gasses will exit on the n/s/r exhaust .. a little on the other side might just be normal condensation or some of the coolant is getting blown back into the inlet tract . The only plus side is you have caught this early and not had a D chunk .

Thanks deMort. Yep - have it at the workshop and my mechanic is thinking head gasket also. So the big question I have to consider is - do I proceed or not? The engine has been well maintained, but it's on 150K. I'm under no illusion that once I get to the gasket I may find more issues and \ or other parts will need replacing. The car is not a garage queen. She has been my daily driver for 8 glorious years but with a clean running engine, I wouldn't have valued the car at more than 10K. A rebuilt engine would boost that but I'm struggling at the moment to justify a Hartech or equivalent rebuild cost. Even man maths doesn't work for me there. I'm capable to DIY it as I could be supported by a mechanic of 40 yrs experience who rebuilds engines for fun, but it will be a big job for me.. The last engine I put together was 25 years ago. I also don't underestimate that this engine will have its nuances - why else are there specialist companies who repair them? Hey ho - it's just a car in the end. A beauty, but just a car

Excellent replies from everyone - just chipping in a couple of points. When the cylinders go oval the front and back dip minutely from the original level they were at when they were round and as the head gasket is a triple metal one it can cause a slight leak but head gaskets by themselves rarely fail (as they are metal and strong). However the other failures we have seen that have similar symptoms are the start of a crack in the cylinder that can be so small initially that cylinder pressure can initially go into the coolant while the engine still runs. Then the crack gets bigger and of course coolant enters back into the cylinder and fouls the plug. If two cracks appear (resulting from the pressure pushing the cylinder in the front to back direction under thrust loads) the cracks taper towards the lower level and eventually meet or the "D" shaped piece falls out or bends too far away to run the engine. D-Mort is (as always) right and offering good advice not to run the engine because if the cylinder fills with coolant it could hydraulic lock the engine and cause a rod to snap and come out of the side of the block and effectively scrap the whole engine. Looks like time to get the head off! Good luck, Baz

That is very interesting , i had wondered why it was always a D shape but had assumed it was hydraulic lock that caused it as the top of the liner was weaker than the con rod so that's the part that failed due to no support . Unfortunately for the OP it means that if a head gasket is a very rare failure then it's more than likely to be cylinder cracks .. I have in the past seen a head gasket failure .. or shall we say that's what i replaced and it was fine for at least 6 years afterwards . Paying for just a head gasket replacement is one thing but a new liner might make this a non viable job as the OP has already stated .... Is it worth proceeding .

Hi All, I find myself in a similar position. In June 2022 I purchased a low mileage(52,000) Sept 2000 996.1 Carrera 4 convertible. The engine number meant it has the earlier dual-race IMS. The idea was a 30th wedding anniversary European road trip. Not a FPSH but the maintenance was good by a Porsche specialist. The car had had a recent oil change in terms of mileage, but it was over 2 and a half years previously, so I decided to change it for the trip. Also, due to the likelihood of hot weather, I upgraded the oil from Mobil 1 5w40 to Mobil 1 5w 50. Changed the filter and added a magnetic drain plug. The old oil was golden and the filter was clean. Before the trip, I checked to water level. A little low so I topped it up. Did the trip; 3020 miles @29 to the gallon and the car didn't skip a beat. Parked it up on the drive and in October popped it in the garage for the winter. One frosty morning after the cold snap I decided to take it for a spin. It started 1st time with no problem. The was a puff of white smoke out of both exhausts but I put that down to the frosty morning which completely disappear after it had idled for a while. The oil pressure was great. Took it for a short run until warm and brought it back to the drive. Let it cool down and thought I would check the fluids. The oil level on the dipstick was good and golden however the water was again low. I topped it up with neat antifreeze (the correct type) and it took 2 liters! I rechecked the dipstick and no trace of water, checked the water tank, and no sign of oil checked the oil filler tube and there was a very small film of what looked like 'copper ease' (nothing white/cream)at the top and in the cap. Having read this thread (there are some knowledgeable Porsche people in it), I am wondering if I have a problem? :?: Any thoughts welcome. Cheers Austin