2007 CL63 Loss of coolant - potential Headbolt failure, advice needed

[unimog]

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?

Were you driving the car when the low coolant light came up? I don't want to sound condescending but is the coolant level sensor working OK? If you think you may have over filled the oil, then it could also be a failing water pump, localised overheating when on a run and then when you park the car up and stop the engine the pressure caps lifts slightly dumping excess pressure and ebulated coolant on your drive. Any unusual drones from the belt driven accessories?

The leakage from the headbolt issue if its only one or two wont show up on a compression or combustion byproduct test unless using much higher pressures than the AA tech did. As I said, after driving and the engine starts to cool down from operating temp, it will likely be a capillary action drawing coolant from the cooling space across the gasket and into the combustion spaces due the head and block dissipating heat and contracting it different rates. It will steadily get worse if indeed this is what is happening.

Oil coolers are not known to be a weak link on these engines, but its not to say it doesn't happen.

 

[Petrol Pete]

OP. Stop driving the car and get the oil tested for Glycol seems to be the general consensus on here.

Get back to us when you get the results , Cheers

 

[Knightrider69]

Were you driving the car when the low coolant light came up? I don't want to sound condescending but is the coolant level sensor working OK? If you think you may have over filled the oil, then it could also be a failing water pump, localised overheating when on a run and then when you park the car up and stop the engine the pressure caps lifts slightly dumping excess pressure and ebulated coolant on your drive. Any unusual drones from the belt driven accessories?

The leakage from the headbolt issue if its only one or two wont show up on a compression or combustion byproduct test unless using much higher pressures than the AA tech did. As I said, after driving and the engine starts to cool down from operating temp, it will likely be a capillary action drawing coolant from the cooling space across the gasket and into the combustion spaces due the head and block dissipating heat and contracting it different rates. It will steadily get worse if indeed this is what is happening.

Oil coolers are not known to be a weak link on these engines, but its not to say it doesn't happen.

Hi the low coolant message came up as soon as I started the car after it had been parked overnight. The day before it was fine with no messages. I'm sure the coolant level sensor is working correctly because the coolant expansion tank was empty. As soon as I topped the coolant up in the expansion tank the sensor/Warning message disappeared.

 

[Knightrider69]

Hi guys so the plot thickens, I couldn't resist the temptation to take the car for a 10 mile test drive. The car drove fine until 9 miles when an error message popped up on the dash saying 'check engine oil level when next refuelling'. I was only 1 mile from home so I drove home and parked up. The engine at this time was up to full operating temperature (approx 95-98 degrees).

i came inside and pulled the drivers manual out and it turns out the difference between the min and max level is 2 litres (not 1 litre which I thought it was). Now I've owned this car for many years and I checked the oil on the dipsticks multiple times over the last day whilst sucking the oil out (at least 15 times). I clearly saw the oil level drop on the dipstick to half way after pulling approx 1200ml out.
Saying that I think it's unlikely the internal engine oil sensor had suddenly gone bad so me pulling 1200ml has taken the oil level below the minimum level.

I've parked the car back up in the same spot and will leave it overnight to completely cool then I will check to see if the level has gone up on the dipstick and/or down in the expansion tank.

I don't understand why I'm getting potential bad/unreliable readings on the oil dipstick. I've never heard of dipsticks going bad but right now I don't trust the readings I'm seeing?

 

[Knightrider69]

Just to add I looked under the car and there are currently no visible oil leaks at present. Will check back tomorrow after the car has sat overnight to see if there are any.

 

[Knightrider69]

Hi guys just back to give an update on this thread and some info that others in a similar situation may find useful. The good news is the car does not have a Headbolt or head gasket issue, the coolant was leaking from the plastic nipple on the thermostat housing. Definitely see that as a win as I was mentally braced for a big repair bill!

A few important points to note:

1. The Mercedes blue coolant stains driveways in a similar way to oil ( I thought the leak was oil as it didn't evaporate and was still visible after various heavy rains
2. Measuring the oil using the dipstick on the m156 engine is very unpredictable in my experience. I sucked out 1200ml as the oil level on the dipstick incorrectly showed it was overfilled. This led to my true oil level going slightly below min which triggered a dash message after driving 9-10 miles.
3. The only way I found its possible to get a true dipstick reading is to start the car from cold for 15 seconds and then switch it off and wait 5 minutes and check. Checking the level after parking over night showed overfill, letting hot engine cool showed overfilled ( this was done on a chalk marked driveway so the car was in the exact same position)

It was a combination of the above points that made me wrongly lean towards a head problem. Glad to have got it so wrong and I hope this info can be useful to someone in the future.

Thank you to everyone who chipped in with their help and advice, it was much appreciated

 

[Steve84N]

Happy days!

My first suspicions were right then and it was separate coincidental issues. I've found to get a correct reading it is best to do it hot after 15mins but take the dipstick in/out about 5 times before you do the actual reading. This clears the tube.

 

[Bobby Dazzler]

Hi guys just back to give an update on this thread and some info that others in a similar situation may find useful. The good news is the car does not have a Headbolt or head gasket issue, the coolant was leaking from the plastic nipple on the thermostat housing. Definitely see that as a win as I was mentally braced for a big repair bill!

A few important points to note:

1. The Mercedes blue coolant stains driveways in a similar way to oil ( I thought the leak was oil as it didn't evaporate and was still visible after various heavy rains
2. Measuring the oil using the dipstick on the m156 engine is very unpredictable in my experience. I sucked out 1200ml as the oil level on the dipstick incorrectly showed it was overfilled. This led to my true oil level going slightly below min which triggered a dash message after driving 9-10 miles.
3. The only way I found its possible to get a true dipstick reading is to start the car from cold for 15 seconds and then switch it off and wait 5 minutes and check. Checking the level after parking over night showed overfill, letting hot engine cool showed overfilled ( this was done on a chalk marked driveway so the car was in the exact same position)

It was a combination of the above points that made me wrongly lean towards a head problem. Glad to have got it so wrong and I hope this info can be useful to someone in the future.

Thank you to everyone who chipped in with their help and advice, it was much appreciated

The correct procedure for the M156 (and some other Mercedes) is to make sure the car is flat and level, and the measure the oil level after EITHER:

1. At least 5 minutes of the engine is at normal operating temperature; OR

2. At least 30 minutes if the engine was NOT at normal operating temperature.

For a consistent reading, option 1 is the best.

Running the engine for 15 seconds and then measuring after 5 minutes will read low. The oil will have been thrown all over the place, and as it will be cold it will be thick and stick to everything it touches and take much longer to drain back down into the sump.

When you measured the levels some of the oil was still stuck to components and will therefore have read low.

Measure at operating temperature and it will whizz back down to the sump in no time: warm oil, is runny oil.

 

[Will]

Hi guys just back to give an update on this thread and some info that others in a similar situation may find useful. The good news is the car does not have a Headbolt or head gasket issue, the coolant was leaking from the plastic nipple on the thermostat housing. Definitely see that as a win as I was mentally braced for a big repair bill!

A few important points to note:

1. The Mercedes blue coolant stains driveways in a similar way to oil ( I thought the leak was oil as it didn't evaporate and was still visible after various heavy rains
2. Measuring the oil using the dipstick on the m156 engine is very unpredictable in my experience. I sucked out 1200ml as the oil level on the dipstick incorrectly showed it was overfilled. This led to my true oil level going slightly below min which triggered a dash message after driving 9-10 miles.
3. The only way I found its possible to get a true dipstick reading is to start the car from cold for 15 seconds and then switch it off and wait 5 minutes and check. Checking the level after parking over night showed overfill, letting hot engine cool showed overfilled ( this was done on a chalk marked driveway so the car was in the exact same position)

It was a combination of the above points that made me wrongly lean towards a head problem. Glad to have got it so wrong and I hope this info can be useful to someone in the future.

Thank you to everyone who chipped in with their help and advice, it was much appreciated

Sounds like a good result...when’s it up for sale then

Only kidding - but from what you’ve said, I’m surprised the AA didn’t spot the leaking thermostat if they went to the trouble of pressure testing the cooling system etc. Usually coolant leaves tell tale marks when it leaks out - but as you say a much better result than what you initially feared

 

[Blazer]

Nervous times have passed.... Glad that it was not to serious...