Coolant missing and can't be found
 

Hello folks,
I bought a used car 2009 with the 6.2 liter M156 engine and 49,000 miles on the dash recently.

The car keeps asking me for coolant. It loses sometimes more, sometimes less but approximately half a gallon on 120 miles. When I topped it up first I thought it was usual consumption. But when it needed more I knew something was off.

I had the car already at multiple mechanics which tried to look for the usual suspects like, hoses, waterpump, radiator, thermostat. Nothing, the car also never has any puddles or viewable drips. They also checked the heating / cooling system which works fine and does not leak.

Despite the car produces no smoke and the oil and coolant caps look normal we performed a chemical test for the head gasket which came back without problems.

Any other suggestions?

Thanks
Mik

I would immediately stop driving it and search head bolt issues on here, it is likely one or more headbolts have failed as it is a known issue on pre 2011 m156 engines they corrode and the bolt heads pop off, if it is just one or 2, you will get a small leak into combustion, not enough to really notice at the tailpipe but a slow reduction in coolant like you have will be noticed. They may not even leak at all when sitting but leak a little when warmed up. You will likely need to replace the headbolts with the updated style and if they have already failed you likely need to remove the heads to get the broken ones out - a lot of people replace them one bolt at a time before they fail but one one fails not sure if there is any way to get it out without pulling the heads. Sorry for the bad news but don't drive it would be my heavy advice as it can eventually destroy an engine. Start with a pressure test and an exhaust gas test of the cooling system. That much coolant without a puddle is being burned likely and with the known issue of headbolts failing that model year it is highly likely that is the issue.

I was having the exact same symptoms as you and decided to change the head bolts and head gaskets. While disassembling, I found a snapped head bolt on cylinder 5 by the driver's side, with the top of the bolt just rolling around the head... Before disassembly: Coolant pressure was holding, I was not getting white smoke out of the exhaust, pistons were dry on borescope examination, and my oil and coolant were not mixing. Unfortunately, this head bolt issue presents insidiously. I hope the same has not happened to you.

Read the FAQ or look around much before posting?

RIP car

Thanks guys. I will bring it in tomorrow to check the screws.
do I need to replace the head gasket too or is this optional ?
I see the replacement screws are made by Elring. How many of those will I need to replace them all?
Thanks

20 head bolts, and yes if the head gasket is compromised you must replace the head gasket, it cannot be re-crushed. Along with the bolts and head gaskets, it is recommended to change the camshaft adjuster bolts and camshaft bearing bolts as well. You must remove the intake manifold, so you will need to replace the 10 intake manifold bolts due to being made of aluminum and are one-time use and the 2 intake manifold gaskets. You also need new valve cover gaskets. Depending on how the job is done as some remove the exhaust manifold from the head, you will need new exhaust manifold gaskets and probably new exhaust nuts and studs. There are certainly more parts to go over but I think those are the main ones? Are you tackling this job alone? Otherwise, just have an experienced M156 mechanic handle everything, assuming you have $$$$$, then no need to worry about all the parts.

Thanks, your help is very much appreciated. Great input !
I will discuss with my mechanic tomorrow.
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Just ran the parts list and thats already 550 plus new oil. Sucks ass...

While you are in there stuff do the pcv as it is cheap and they fail often and are easy when I take is off. Inspect lifters but a good time to replace with updated ones put is 600 or so for them. Injectors are about 250 a set and 50k miles is a good time to change them before they leak and hydro lock the engine. Last but not least since cam adjusters are out if you have startup rattle might be time to rebuild the plate which is like 800 ish for parts.

How long ago did you buy it and what are your state's lemon laws? This could be a $4-5k job depending on the shop.

Does your washer fluid smell like coolant?

Coolant pressure test. Head gasket compromised if coolant reservoir begins bubbling. Snowball's chance in hell all your head bolts are intact.

I would really look into your options because this is only the tip of the iceberg and while your car is already disassembled, it would make sense to iron out the rest of the wrinkles these cars present.

Cams (possibly), lifters(absolutely), injectors (may as well, you're clocking 50k and the injectors maybe have another 15-20k of life left), and motor mounts (these always need to be repaired and you're just buying time and saving on labor doing it now) just to start.

+ Belts and idler pulleys. I changed mine at 70k before something broke and causing a bigger headache.

What is the pcv? You mean the valve lifters and fuel injectors? What lifters cost 600 bucks? Why would you change the lifters if the engine does not make the clicking noise when accelerating?

No, normal.

I live abroad. I could sell the car or repair or. Or drive it until it is toast.

Which belts besides the serpentine?

PCV is attached behind and below the intake manifold on the main block and attaches behind the passenger side cylinder head, around $100, MBWorld has an official article somewhere that details its replacement but it is very easy to do with the intake manifold off. I would recommend replacing the fuel injectors for peace of mind, they are around $300 for 8 of them which is much cheaper than totaling your car due to hydrolock. You do not need to change your lifters immediately, just inspect first if they have any linear scratches or other major wear marks to make a decision. Mine were perfect at 110,000 miles but I bought replacements anyway for $300, obviously ymmv.

A specialist near me with stellar reviews quoted $4500 for head gasket replacement labor, parts NOT included! They said that if a head bolt is broken, they would charge even more.

one of the first two is your best financial option

#3 will be soon if you keep driving it.

We started but struggle already.
Any idea where I can get a tool to remove the camshaft?

If I were in your situation I would stop immediately until I could find a competent mechanic to perform this work.

What do you mean, the camshafts come out with basic hand tools, a few torx head sockets

There is no shame in admitting you're above your paygrade.

Plenty of people pay other people to do work on their cars. Especially this kind of work.

The world of nuance you're about to enter is incredibly unforgiving.

The wrong decision would be making an ego save attempt and not biting the bullet and eating it.

Everyone gets screwed on cars no matter what so don't take it personally.

If you can't find someone to do the work, your best bet is to cut your losses where they are, sell/trade the car and inform the person you're dealing with what you found.

This is how far my mechanic got.
https://cimg8.ibsrv.net/gimg/www.mbw...9e67082e22.jpg


In order to move on we need a special tool like this