Intermix 996.1 3.4 c2

Hi all, my first post on this forum (which is excellent btw). Grateful for your advice guys on my 1999 911 996.1 3.4 c2 tip which I have owned for 18 months. 113k miles. FSH Porsche or specialist. It’s a familiar story on the M96 engine which has an intermix problem with oil in the coolant and vice versa. Checked the oil filter and couldn’t see any metal fragments. Next step I guess is a borescope? I have been quoted £250. Quick history: At time of purchase temperature gauge was steady 80-90 never wavered. No coolant loss. Winter 2024 car suddenly started overheating & losing coolant. I changed the coolant cap for the OEM04. No difference. The fans stopped kicking in so I had Charles Ivey replace the thermostat sensors which was circa £900. This fixed the fan problem. Drove the car out of Charles Ivey and the temperature gauge immediately started flashing red. I was told the car had been running fine and likely had air pockets in the coolant system. So off to the nearest steep hill I went and topped up the coolant whilst trying to burp the system. And it seemed to fix the issue. I had the car serviced last year at Porsche Chiswick and no problems reported. (I spent a tonne tho on getting the AC working. Replaced both compressors which had the usual stone chip damage. This still didn’t fix the problem and I had to replace the damaged pipes. That was a tough lesson people. NEVER fall for the old “just needs a re-gas” line when you buy a car. If it just needs re-gassing get the seller to do it!) Anyway not long after that my coolant issues returned. Car was running hot and the coolant top-ups started to become more frequent. For the life of me I could not find where the coolant was going. No external leaks. Reservoir seemed fine. Exhaust started smoking white at startup but then seemed to burn off and went back to normal. (I’m still naively thinking air pockets here). And then just like that I checked the coolant one day and found this peachy/strawberry milkshake texture. Engine bad! White smoke from bank 2. Now slight dribble of coolant on nearside rear above wheel. No soot in exhaust tips. No oil loss. But def coolant in oil. EML has just come on and car is suddenly sounding rough. I have parked the car. I have only driven a few miles with the milkshake. No miles since the EML. Given the above I’m self diagnosing cracked cylinder head. But seriously, without further work what do I know?! Here is my question. Sorry it’s taken this long to get to the point but I thought it might help others that might encounter the above. A local Porsche specialist has explained that we won’t know what the actual problem is until we start taking it apart. Whether it’s gasket (unlikely?) cracked block repair or replacement, or IMS bore score/full rebuild. It seems vague. The specialist will disassemble and send the engine block to someone else for the machine work. And it will likely take 10 weeks. It could be £3k, £5k, £10k he doesn’t know until they start. Would a borescope tell me which? I would imagine there is scoring regardless after 26 years and 113k. Does the above sound right? I’m worried about a one man specialist (reasonably priced according to reviews) taking everything apart and then im totally held hostage with my engine god knows where. Since joining this forum I have read great things about Hartech and a lot of insightful comments from Bas and Grant. I always dismissed this as an option as I was under the impression that Hartech were expensive. But is that an urban myth? They seem really good and now I’m thinking if it does require any engine rebuild would a reputable brand like Hartech be the much better option than an unknown independent? I’m thinking if I ever sold the car (over my dead body) the name and reputation would make a big difference. And put my mind at ease. Conversely, if Hartech do the work and my wife finds out the price am I still thinking dead body here? Help! Thing is I love my car. It’s not a turbo. It’s not a c4s. It’s a 3.4l but god does it put a smile on my face. The cable throttle is really the last of the analog. I drove a 997. But it lacked that same feeling. If that makes any sense. Anyway sorry for the jackanory. Thoughts and suggestions would be gratefully received. Cheers, Greg

Bt the sounds of it you've got a cracked head/block and or gasket but it could be the oil cooler that's failed , very hard to tell until you get it up in the air and pull it apart. Bare in mind the 3.4 shares cylinder heads with the 3.2 Boxster and they're readily available so don't panic too much , 3.4s don't suffer bore score and symptoms aren't there either.

I don't think a boroscope inspection will tell you very much here. If you have oil in the coolant, it'll be everywhere in the system and sticking a boroscope in will probably be inconclusive. As Uncle Monty says, it has to be stripped and inspected. There's a chance it's the oil cooler/heat exchanger! But yes, it's probably the cylinder head.

Before anything else try buying a couple of bottles of Steel Seal from Halfords. Should fix minor head cracks and gasket breaks. I was very sceptical but it fixed similar issues with my 3.4 c2! Worth a shot for £80

Possibly oil and coolant heat exchanger

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Thank you for your reply. You’re right im probably panicking too much. I had the car up on a ramp and couldn’t see any leaks from the oil cooler. Externally at least. I had no idea the block is shared with the Boxster. Thats good intel! Same here I didn’t think bore score was an issue on the 3.4 prior to 2000.

Awful situation to be in, I think it’s most 996 owners worst nightmare. As others have said oil cooler is known failure also history of 3.4 cylinder heads cracking. They can be repaired or replaced. I think it’s unlikely you’re dealing with borescore here, I wouldn’t rush to borescope it, if it’s not an oil cooler failure it’s going to need stripping anyway, you can properly inspect the bores then. Do you have skills to work on it yourself? If not I would find an Indy you 100% TRUST. If you’re in anyway worried about them don’t use them, one thing we’re not short of in the UK is independent Porsche specialists! I would suggest you agree a set amount of labour time with them to investigate the fault. If they say it needs stripping then you can decide where you go from there. Option 1 Sell it and get out Option 2 Take the plunge, Strip it and find out what you’re dealing with, only then can you really know what it’s going to cost to put right. The engine rebuild subject has been covered many times and ultimately it comes down to the individual what they decide to do.

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Thanks for your feedback. Agreed I don’t think borescope will prevent engine out. I feel the £250 is better spent on any rebuild. No obvious leaks from the oil cooler but not ruling it out. I’m convinced the failed thermostat sensor caused this issue. Do you know how long it takes to repair a cracked head? It looks pretty labour intense.

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Thank you! If it doesn’t work does it cause more work in the long run? Or is it a free £80 shot do you think?

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Fingers crossed! But I’m stealing myself for the worst.

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Thanks for your sound advice. Yeah It feels like I’m stuck between a rock and a hard place. I got a quote from webuyanycar for £4K which is nothing compared to what I’ve spent on the car already. My thinking is get the work done and I get to keep my 911 on the road. I can’t afford to bulletproof it. But if there is no secondary damage and other parts are not at the end of their life then I’m hoping the costs won’t get too high. But of course we both know that once you start swapping parts out it starts a domino effect.. If I sold the car and just get out then I’m back in TT territory. And I mean no disrespect as my TT 3.2 Quattro was really nice. But when you sit in a 911 it’s a whole different level. I keep telling myself to forget what I paid for the car and for the work so far. That’s all in the past. Looking ahead if it costs £5-6k I should be all set for a 911 future. But it’s so hard to throw off that “good money after bad” feeling!

Free shot… it’s like an advanced version of radweld. It’s well regarded, and like I said I was sceptical until I used it!

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Thank you I will be sure to check it out!!

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The journey of owning an old Porsche, it’s not for the faint of heart! Best of luck Let us know how you get on ..

Before you go any further there is a simple test that you can do to ascertain whether you have a head gasket or cracked head (or cracked anything else for that matter). You will need to buy https://www.ebay.co.uk/itm/39634878...teid=0&campid=&customid=&toolid=10001&mkevt=1 Simply unscrew the cap from your header tank, fit the appropriate cap from the tester kit, attach the pump and pump up the pressure to say 15psi. Now go and have a cup of tea and when finished check the pressure reading which, if all is well with the integrity of the cooling system should still show 15psi. Now the 'big one'..... with the pressure tester still connected start the engine and let it idle. If the pressure reading is stable at 15 psi you DO NOT have a cylinder head/gasket issue. IF there was a problem the pressure gauge would 'pulse'. This is because as the pistons rise and fall combustion gas would be forced via any crack into the cooling system increasing the pressure in the cooling system and hence the 'Pulse'. If all is good then the next stage is, with the tester still connected and pressurised, to let the engine heat up. This will allow the engine to expand and again if there is an issue which only occurs when the engine is hot...to show its face. That then for just £26 and a cup of tea should point you in the right direction. I hope this helps.