2007 CL63 Loss of coolant - potential Headbolt failure, advice needed
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Steve84N
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Hydro locking is usually when some fluid gets in the combustion chamber, this can be water through the air intake, coolant seeping in or fuel from a stuck injector. As fluid is incompressible then you typically start breaking stuff, like bending conrods.
Too much coolant/fuel in the chamber can also wash the oil off the cylinder bores leading to damage to the walls.
It's really not a good idea to drive it to find out what's wrong. If it is serious the more you use it the worse it will get and the damage could quickly rise.
Too much coolant/fuel in the chamber can also wash the oil off the cylinder bores leading to damage to the walls.
It's really not a good idea to drive it to find out what's wrong. If it is serious the more you use it the worse it will get and the damage could quickly rise.
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Knightrider69
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Ok thanks for that explanation, so am I right in thinking that if the coolant is leaking into the oil sump and the engine is running as normal without misfire or white smoke that the chance of hydro locking is low? Does anyone know of anyone with a m156 engine that was hydro locked after head gasket failure?
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Knightrider69
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Yes that makes sense, I think the best thing to do right now is send the oil I've pulled off for this bronze analysis. That will give us a pretty conclusive answer on if there is coolant in the oil or not.
Steve84N
MB Enthusiast
I don't. The hydro locked engines are more commonly stuck open fuel injectors.
Just because it may only be leaking into the sump now doesn't mean it won't progress into up top as well though...
Just because it may only be leaking into the sump now doesn't mean it won't progress into up top as well though...
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Knightrider69
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I'm just very surprised at the oil that I pulled out through the dipstick, it looks completely normal. As others have mentioned in this thread oil and water don't mix so I don't understand how it's possible. I will take some photos of the oil I pulled tomorrow and mixed with coolant to show you guys. Very confusing!
Not going to do the engine a lot of good running on gradually diluted engine oil with coolant in it, if that is where you are now. I wouldn’t keep driving it, sorry but I think it is for the best until you have your options in front of you regards the fault and the repair.
You have a good few litres of oil in the M156, oil also floats so you might not have caught it on the dipstick - I would drain the oil (or coolant!) from the sump
You have a good few litres of oil in the M156, oil also floats so you might not have caught it on the dipstick - I would drain the oil (or coolant!) from the sump
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I wouldn’t worry about hydro locking it specifically. Just don’t drive it u til you have the results back from the lab. That can only be a good thing.
I’ve done a few head gaskets in my time, where by oil and coolant has mixed. If you leave it sitting for long enough you can often drain clean coolant/water straight out of the sump plug!
Does the M156 happen to have additional oil coolers that are linked to the coolant system? Never had the need to look into this but it would be another possibility for them to mix.
Does the M156 happen to have additional oil coolers that are linked to the coolant system? Never had the need to look into this but it would be another possibility for them to mix.
Steve84N
MB Enthusiast
In the C63 there is an additional oil cooler in the lower side of the front grill but it's not linked to coolant. It's just air cooled and has a fan.
Its unlikely to hydrolock the car in the case of failed head bolts, it may only be one bolt that's failed and has released tension in a particular point on the head affecting maybe 1 or 2 cylinders, a borescope exam will find it. Not driving or thrashing the engine will stop the others from breaking or releasing tension.
As the engine cools the coolant will seep into the bores and past the rings into the sump. Coolant in the oil will reduce lubricity, so its more likely you will score or 'run' bearings by continuing to drive the engine. If you drive it you risk damaging main, bottom end, and cam shaft journal bearings, not to mention scoring cylinder liners due to lack of cylinder wall lubrication. The M156 has oil cooled pistons, so there is also a good chance of melting one as the coolant coagulates in the oil galleries and starves oil flow to the cooling jets on the underside of the pistons. Not quite Mercedes (but an old Merc design), but I have just had a 3000hp MTU396TE94 V16 engine do exactly this due to a leaking charge air cooler.
In short: Change the oil now to get any contamination out. Dont drive it. Dont play diagnostic darts and dont be under the illusion it will be OK, get a specialist involved.
As the engine cools the coolant will seep into the bores and past the rings into the sump. Coolant in the oil will reduce lubricity, so its more likely you will score or 'run' bearings by continuing to drive the engine. If you drive it you risk damaging main, bottom end, and cam shaft journal bearings, not to mention scoring cylinder liners due to lack of cylinder wall lubrication. The M156 has oil cooled pistons, so there is also a good chance of melting one as the coolant coagulates in the oil galleries and starves oil flow to the cooling jets on the underside of the pistons. Not quite Mercedes (but an old Merc design), but I have just had a 3000hp MTU396TE94 V16 engine do exactly this due to a leaking charge air cooler.
In short: Change the oil now to get any contamination out. Dont drive it. Dont play diagnostic darts and dont be under the illusion it will be OK, get a specialist involved.
That's not strictly true anymore that oil and water dont mix in this sort of scenario, and its a modern bain in engine fault diagnosis. Both high performance oils and coolants for modern Bi-metallic and all alloy engines have emulsifying agents formulated into them to trap particulates in the oil or cooling system, and therefore only precipitate large quantities of contaminants like water or oil/fuel in the case of coolants. A litre of coolant as you indicate you may have lost could readily be suspended in around 9-9.5 litres of sump oil which I think the m156 holds.
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Knightrider69
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Hi thanks for your detailed reply, if a bolt has failed and released tension in one point on the head gasket would you expect that to be picked up on a head gasket test where gases are checked in the coolant expansion tank? My car passed the head gasket test?
I will be sending the oil off for analysis to see if it definitely had coolant in it (which I highly suspect it does). This issue then becomes on whether it's leaked through the head gasket or somewhere else eg oil cooler. I'm hoping the head gasket test pass is good news but it's been suggested that this engine could have passed the head gasket test and still be leaking which I don't understand?
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Knightrider69
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Hi some interesting observations regarding the oil I extracted last night. After removing 1200ml I took 60ml of it and added approx 20ml of coolant. At the time the coolant mixed in and apart from looking a bit thinner it looked the same as the original extracted oil.
I came back to the oil today and the oil that I added coolant to has now changed colour and has become a milk/dark chocolate colour. There also seems to be some coagulation present at the bottom of the container. The Original oil that I pulled from the car has the typical dark Coca Cola colour and the difference is quite noticeable.
I have added a photo, on the left is the original oil and on the right is the oil I added coolant to.
Another point I didn't mention earlier was I noticed a oil patch on my driveway a few days before my low coolant message came up. The patch seemed to be near the front of the engine area.
I'm not sure if these 2 incidents are related, I topped 900ml of oil a few weeks ago when I last checked as my oil level was showing as minimum on the dipstick (have been topping it periodically up for years). Saying that I can't rule out that I have somehow overfilled the oil and the coolant leak could be somewhere else and getting burned off?
I came back to the oil today and the oil that I added coolant to has now changed colour and has become a milk/dark chocolate colour. There also seems to be some coagulation present at the bottom of the container. The Original oil that I pulled from the car has the typical dark Coca Cola colour and the difference is quite noticeable.
I have added a photo, on the left is the original oil and on the right is the oil I added coolant to.
Another point I didn't mention earlier was I noticed a oil patch on my driveway a few days before my low coolant message came up. The patch seemed to be near the front of the engine area.
I'm not sure if these 2 incidents are related, I topped 900ml of oil a few weeks ago when I last checked as my oil level was showing as minimum on the dipstick (have been topping it periodically up for years). Saying that I can't rule out that I have somehow overfilled the oil and the coolant leak could be somewhere else and getting burned off?
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Steve84N
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Well one of my earlier theories is that the two aren't actually related... The oil analysis will really help get a better idea of what fluids are going where.
What does the leak on your drive look like now, can you take a photo? Oil tends to stay unless you really wash it off with degreaser etc whereas coolant dries up and might just leave a bit of residue or be washed away in the rain.
What does the leak on your drive look like now, can you take a photo? Oil tends to stay unless you really wash it off with degreaser etc whereas coolant dries up and might just leave a bit of residue or be washed away in the rain.
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Knightrider69
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I've added a photo of the stain, I put a tennis ball next to the patch for scale. We have had some pretty heavy thunderstorms over the last few weeks and the car isn't parked on the drive at the moment so some will have been washed away.
I'm in 2 minds now whether to risk doing a short test drive to see if my oil level goes up again or whether to send a sample off for analysis as the analysis is going to be at least a week before I get results. The oil that I have pulled out doesn't have any coagulation or visible signs of coolant contamination. The safest option is definitely to not drive the car and send the oil away I agree but with all the other factors it might not be as risky to test drive it
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The head gasket test your car passed was only a test for combustion gases leaking into the coolant; the pass has no relevance to a coolant leak into the oil.
I'd not drive the car until you have the result of the glycol test on the engine oil. If it passes, the two 'faults' are unrelated, and the head gasket is fine; if not, you could have harmed the engine by driving it further.
"Do ya feel lucky, punk? Well, do ya?" Your choice...
I'd not drive the car until you have the result of the glycol test on the engine oil. If it passes, the two 'faults' are unrelated, and the head gasket is fine; if not, you could have harmed the engine by driving it further.
"Do ya feel lucky, punk? Well, do ya?" Your choice...
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Knightrider69
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Haha that's just it, this punk is feeling lucky. I'll sleep on it tho!
Your car passed a combustion gas test on the coolant, as mentioned already. This isn’t a head gasket test although they may have said that at the time.
In simple terms, you have a coolant jacket around bores (in the engine block itself) and coolant passages in the head. When the two are bolted together, the gasket between them is what forms the seal and stops leaks as the coolant is circulated around the complete engine. The head gasket also seals the bores in the engine block (where the pistons are) to the combustion chamber area of the head (where the valves and spark plugs are) and you also have oil passages that go from the heads and back to the block as it lubricates the camshafts and valvegear etc and oil is returned to the sump.
You can have a leak from the coolant passages or the oil passages or the combustion area, or all three (!) either to themselves or externally. They all share the same gasket (the head gasket) but are separated. The head gasket can leak from the oil or coolant passages into each other without affecting the cylinders hence the check needed on the engine oil for glycol going by what you have said.
Not sure if you saw my post regards your oil sample - it sounds as though you’ve taken it from the top via the dipstick tube. It’s possible that some coolant may be sitting on the bottom of the sump if it had been standing. Even if it was mixed evenly and suspended within the oil it might not look that visible to the naked eye if it’s only a few hundred millilitres in 8/9L of oil old.
I would drain say 1/2 litre of oil out of the sump into a clean container and check it and take some for a glycol sample, it’s just not worth the hassle of driving it as you could really make this worse. If it breaks big time you won’t be driving it anyway, probably worth remembering!
Fingers crossed you’ve caught it early, and it could just be head gaskets, bolts and fresh fluids etc. Rather than further damage
I must say I like the idea of an external coolant leak and some confusion over the oil level, although I think that does sound like wishful thinking if you’ve had the car for 3 1/2 years - chance of misreading the oil level that much is surely quite low? And if they pressure tested the cooling system an external leak should be easier to spot - you’d see residue from the coolant (and smell it too!) anyway.
But there is of course hope, glycol test would give you more to go on here.
