CLK320 very high oil consumption

[Mo420]

Hello all,

Ok so here's the story, my dad owns a 1997 w208 CLK320 sport coupe with the M112 V6 3.2L engine, mileage is currently around 125k kms. I have only started driving the car daily quite recently as I just sold my previous daily driver and currently waiting for a good deal for a new car.

Anyway, the problem with the CLK is that it has started to consume oil. Initially it wasn't too bad, just needs a top up every now and again between oil changes, and we managed to isolate the problem to leaked valve cover gaskets. This went on for quite a while (thought it wasn't an urgent repair) before we got the gaskets finally replaced last few months.

So now, here's the real issue. So far, after replacing the gasket, the oil consumption problem hasn't gone away, in fact it has only been getting worse. Much much worse, as currently it's consuming around 1L of Mobil1 5w-50 fully synthetic every 500kms! So far I haven't seen any oil droplets (used to have these before the gasket replacement) on the garage floor nor on the metal tray under the engine, its all been fairly dry so I'm fairly sure it isn't caused by yet another oil leak somewhere.

Car drives fine, pulls great and kickdowns well etc etc. Only symptom is on most of the cold starts in the mornings (used to happen only once in a while now happens in 95% of cold starts) - I get a bluish smoke coming out of the exhaust, happens for about a minute or two, i.e. happens during fast idle only and stops when the revs start settling down to normal idle. After that, no bluish smoke whilst driving (no signs of smoke in my rearview). Another thing is, in one of the cylinders, cylinder 4 I think (front most, passenger side on my RHD vehicle), keeps getting very bad carbon buildup on the spark plugs. My last set of plugs lasted for only about 10,000kms I think .

So far, the symptoms are pointing out to possibly an oil burning issue in cylinder 4 (maybe could also involve other cylinders). I'm not very well versed on these engines so please do feel free to share any thoughts/experiences/info/comments on a possible fix for this, massive thanks in advance!!

Cheers,
Mo420

 

[Hawkwind]

Hi, I think your probably correct in thinking the oil is being burnt and if the spark plugs in cylinder 4 are fouled then you've probably got your culprit.

Another thing you can check is the exhaust pipe (when it's cold), wipe your finger around the inside surface to see what you get. Dry sooty deposits usually indicate the fuel mixture is too rich, while a black oily deposit indicates the engine is burning oil.

Has the car been properly/regularly serviced and have the correct spark plugs always been used? If properly maintained these engines are very reliable, mine has done over 100,000 miles (about 150,000 kms) and has not used any oil since I serviced it in Febuary this year.

The only other suggestion I can think of is to check for oil in the cooling system, though I think you'd have noticed overheating issues, so from your description, not very likely.

 

[merc85]

What's the recommended grade ? 5w50 seems abit thin ? Maybe wrong, also it could be valve stem seals, perhaps a compression test maybe next course of action?

 

[herby thr cls]

Car drives fine, pulls great and kickdowns well etc etc. Only symptom is on most of the cold starts in the mornings (used to happen only once in a while now happens in 95% of cold starts) - I get a bluish smoke coming out of the exhaust, happens for about a minute or two, i.e. happens during fast idle only and stops when the revs start settling down to normal idle. After that, no bluish smoke whilst driving (no signs of smoke in my rearview).

I would think that the valve guide seals are worn on cyd 4, and letting oil drip into the cyd overnight, hence, blue smoke when starting from cold and then clears pretty quick

 

[Mo420]

Hello all,

Thanks very much for your helpful replies so far

The car has been fairly well maintained and serviced, although I would admit the oil change interval sometimes stretches to around 15k kms when our work schedules get hectic, but mostly we make sure to change oil around 10k kms with genuine or OEM filters.

There are black soot deposits on the exhaust tip, I'll check later to see whether its oil or fuel as you have suggested. No oil in the cooling system.

Regarding the oil grade (5w-50) do you guys think its quite thin? What grade do you guys use? I've checked the manual for recommended grades and 5w-50 is kind of ok for our tropical climate. We have used 10w-40 during the previous oil change since my mechanic also suggests using a thicker grade oil to see if it the consumption issue improves slightly (it didn't) but I'm having my doubts about using Semi-Synthetic oils in the M112 as I've read about members with sludge issues due to these (happy to be proven wrong on this). Manual doesn't mention this though, just states it should be to MB 229.1 spec. If I'm actually inclined to try SAE40 single grade oil next time around if indeed fully synthetic oils are not a must.

From my research so far, I am also leaning towards valve guide/stem seals... however if its just burning oil during start ups due to these seals, would it justify the excessive oil consumption (1L every 500kms)? We often do only short distance driving so if you can imagine we only drive about 10 kms to 20 kms between start ups. Long distance driving is very rare as Brunei is a small country I'll try look up compression testing as suggested, thanks for that. Do you reckon worn piston rings also be a possible cause?

Cheers,
Mo420

 

[Mo420]

Also, regarding valve stem seal replacments, how big of a job is it you guys reckon? I'd probably send the car to an indy for this job as it sounds like a major repair. Am I correct in thinking that would need the cylinder head to come off? And also I imagined it'd be worth replacing all seals not just for cylinder 4 whilst the head is off? Either way, the valve cover gasket will need to be removed and replaced. Again. Oh well.

Cheers,
Mo420

 

[SLKNick]

Normal procedure for valve stem seal replacement calls for the cylinder head to be removed, in which case it is a no brainer to do them all.

However, it is worth considering the rope trick which means you don't need to take the head off but you still have to remove the valve cover, camshaft and timing chain.

 

[rorf]

1 litre per 500 kms is excessive

229.1 is definitely not the spec for this engine - it is 229.5 and Mobil 0w40 is the recommended oil. For sure you have a leaking valve seal at No 4 or I think more likely a broken piston ring.

What ever the first thing to do is a compression test on all cylinders and then a leak down test on No 4.

I see your engine must be one of the first produced and were known to have piston skirt problems. The latter engines are bullet proof - mine has 220 000kms and uses no oil and I change it every 2 years or 18 000kms

Good luck.

 

[rorf]

You mention the last set of plugs only lasted 10 000kms? I trust you are using the correct Mercedes Bosch platinum plugs which should last 160 000kms!

Incorrect plugs can easily contribute to your problems.

 

[190]

Regarding the oil grade (5w-50) do you guys think its quite thin? What grade do you guys use? I've checked the manual for recommended grades and 5w-50 is kind of ok for our tropical climate. We have used 10w-40 during the previous oil change since my mechanic also suggests using a thicker grade oil to see if it the consumption issue improves slightly (it didn't)

5W50 is thick oil. It's a common misconception to focus on the 5W bit and consider the oil as as being thin. The 5W part means the oil is thin when it's cold which is a good thing although 0W is even better. At operating temperature your mechanics suggested 10W40 is actually thinner than 5W50.

Although 0W40 is the correct oil grade 5W50 might be appropriate in an very hot climate. It all depends on oil temperature as the engine has no clue what grade of oil is in it. It only knows how thick the oil is at the temperature it's operating at so if the oil is hotter than normal then 5W50 might be OK otherwise it's too thick.

 

[WG M-B]

The m112 suffers from breathing issues when oil intervals are ignored.
I would remove the breather pipes on the rocker covers and check the drain back to the block is working.
If not then your inlet probably has a nice deep puddle of oil sitting in it.
Which will cause excessive consumption!
You could well have an issue on only one cylinder, and if this is the case then it can be tested quite easily

 

[merc85]

5W50 is thick oil. It's a common misconception to focus on the 5W bit and consider the oil as as being thin. The 5W part means the oil is thin when it's cold which is a good thing although 0W is even better. At operating temperature your mechanics suggested 10W40 is actually thinner than 5W50.

Although 0W40 is the correct oil grade 5W50 might be appropriate in an very hot climate. It all depends on oil temperature as the engine has no clue what grade of oil is in it. It only knows how thick the oil is at the temperature it's operating at so if the oil is hotter than normal then 5W50 might be OK otherwise it's too thick.

5w is thinner than 10w when its cold, if there is a leak ie Valve stem seals on 1st start up its more likly to smoke isn't it?

 

[190]

5w is thinner than 10w when its cold, if there is a leak ie Valve stem seals on 1st start up its more likly to smoke isn't it?

Well maybe but the benefit of thin oil from a cold start far outweighs any concern for consumption. No one should be using thicker oil as a cure for consumption instead of fixing the root cause. Oil being too thick when it's cold is what we should all be worrying about. I'm an oldie brought up on 20W50 with a preconception that something like 0W40 is like water by comparison but when you look at the figures it simply isn't the case. the difference between 0w40 and 20W50 at 100 deg C is relatively small. But at a 0 Deg C cold start the difference is huge. To put numbers on it at O deg C the 0W40 will be approx. 550 cSt and the 20W50 over 5 times thicker at 2900 cSt. At 100 Deg C the figures are 14 cSt vs 18 cSt so not such a big difference and won't have a huge impact on oil consumption. I don't have a graph which includes 0W40 but here's one comparing 5W40 with a range of thicker oils. The line for 0W40 would be a little below the 5W40. What it illustrates is that all oil is vastly too thick when cold and that's bad for your engine. 0W oil is at least thinner than the others and if they were able to produce -5W oil although still too thick when cold, it will be the best oil to have.

 

[merc85]

Agree totally, a mechanucal defect should be fixed properly.

 

[KeithJG]

Well maybe but the benefit of thin oil from a cold start far outweighs any concern for consumption. No one should be using thicker oil as a cure for consumption instead of fixing the root cause. Oil being too thick when it's cold is what we should all be worrying about. I'm an oldie brought up on 20W50 with a preconception that something like 0W40 is like water by comparison but when you look at the figures it simply isn't the case. the difference between 0w40 and 20W50 at 100 deg C is relatively small. But at a 0 Deg C cold start the difference is huge.

You being an oldie should know better......Lol

I am an oldie also but all this talk of oils is just marketing and modern technology......you don`t need 0W or even 5W for cold starting in this country and 20W50 like Duckhams i used in all my old performance motors and had no problems with winter starting at all. Thicker oil is still around the bearings just as thinner oil is and if you think about it i would rather have a heavier oil around them than thinner for starting!.....the thicker oil clings more than thinner. If one sticks to 2000revs while warming up that will do more good than a thinner oil....the only thing in this country that the thinner oil is good for is that it is not such a drain on the battery but then the volts are soon put back as we now have alternators and not like we had in the `60`s etc. dynamo`s.

Of course it is better to have an engine that is in top condition BUT having a heavier oil if it solves the condition then it will put off any expense until it really really needs attention.

These "green" synthetic modern oils are for more modern engines with VVT etc. and for longer servicing intervals if the oil is heavier the VVT pulley will mess up and fail.

Some manufacturers state use 0W30 but they fail to recognise when the engine gets older and has a higher mileage that they could do with a heavier oil.....why do you think you can get heavier oils , why do they produce them?

I put 10W40 in my diesel Zafira when bought and it was quiet and sweet as a nut considering it is not a very refined engine but when i didn`t have time for a service it was taken to the Vauxhall dealer and it came out rattling like a pig and oh so noisy even from inside the car, yes, they had put in 0W30 and it doesn`t have VVT like the petrol engine.

As said above it is probably the stem seals gone hard after all those years since 1997 and not so much wear because of mileage.....so being an oldie at least you do know the best thing to do.

Good Luck.

 

[Mo420]

Hi all,

​

Thanks for your very helpful responses.

​

1 litre per 500 kms is excessive

229.1 is definitely not the spec for this engine - it is 229.5 and Mobil 0w40 is the recommended oil. For sure you have a leaking valve seal at No 4 or I think more likely a broken piston ring.

What ever the first thing to do is a compression test on all cylinders and then a leak down test on No 4.

I see your engine must be one of the first produced and were known to have piston skirt problems. The latter engines are bullet proof - mine has 220 000kms and uses no oil and I change it every 2 years or 18 000kms

Good luck.

​

I have just checked my User’s Manual to confirm this, and yes it does say engine oil specification should be to MB approval 229.1. I’ve heard that MB changed to 229.5 in the later models. As for my oil grade (I know this is quite a controversial issue, I’ve seen lengthy discussions regarding this in a lot of forums especially BITOG), but I did check based on the manual that 5w-50 is indeed acceptable for our fairly high ambient temperatures here, where it ranges only between a minimum of 24 deg celcius to around 35 deg celcius maximum.

You mention the last set of plugs only lasted 10 000kms? I trust you are using the correct Mercedes Bosch platinum plugs which should last 160 000kms!

Incorrect plugs can easily contribute to your problems.

I will need to check on this again – I’ve always bought them at this specialist MB parts center and I’m pretty confident regarding their credibility. They do get pretty fouled up quicky, especially those in cylinder 4 (all cylinders use the same plugs just in case you were wondering) to the point of causing random misfires. Like I said last time, both of cylinder 4's plugs had to be replaced just after 10k kms!

​

However, just in case I’ve used wrong plugs, would it be possible for these wrong plugs to cause severe engine oil (not fuel) consumption as is my case?

5W50 is thick oil. It's a common misconception to focus on the 5W bit and consider the oil as as being thin. The 5W part means the oil is thin when it's cold which is a good thing although 0W is even better. At operating temperature your mechanics suggested 10W40 is actually thinner than 5W50.

Although 0W40 is the correct oil grade 5W50 might be appropriate in an very hot climate. It all depends on oil temperature as the engine has no clue what grade of oil is in it. It only knows how thick the oil is at the temperature it's operating at so if the oil is hotter than normal then 5W50 might be OK otherwise it's too thick.

We do mostly urban driving, and I’ve noticed the temperature gauge points around 90 to 100 degrees whilst driving in the city and more towards 80 to 90 degrees whilst cruising on the highway. I should think that 5w-50 is pretty much spot on don’t you think?

The m112 suffers from breathing issues when oil intervals are ignored.
I would remove the breather pipes on the rocker covers and check the drain back to the block is working.
If not then your inlet probably has a nice deep puddle of oil sitting in it.
Which will cause excessive consumption!
You could well have an issue on only one cylinder, and if this is the case then it can be tested quite easily

​

Thanks for suggesting this. I’m interested to learn about this, am I right in saying that each of the rocker covers either bank only has one breather pipe each? Whereabouts are the ‘inlet’ and ‘drain back’ pipes located?

​

Just another thing to add whilst we are at this point, we actually replaced the rocker covers (both sides) with new ones when we did the gasket replacement as the old rocker covers appear to be disintegrating (based on my judgement anyway lol ). Anyway, during the replacement, we also put on new breather hoses. Mind you this was only about 5,000kms ago and I’ve inspected the breather hoses just now, they appear to be clean. Are there other areas within the crankcase ventilation system that I should also look into?

You being an oldie should know better......Lol

Some manufacturers state use 0W30 but they fail to recognise when the engine gets older and has a higher mileage that they could do with a heavier oil.....why do you think you can get heavier oils , why do they produce them?


Good Luck.

I’ve read elsewhere in this forum and also other MB forums that the M112and M113 engines are quite prone to sludging issues if non fully synthetic engine oil are used. Anyone care to shed a light on this?

​

As said above it is probably the stem seals gone hard after all those years since 1997 and not so much wear because of mileage.....so being an oldie at least you do know the best thing to do.

Good Luck.

At the moment, the stem seals is the most probably issue here. I guess the smokey cold start symptom tells a lot.

​

I am thinking, if it were a problem with the piston rings, the car would smoke all the time wouldn’t it? I was tailing my CLK, which was driven by my dad during a family trip this weekend and the exhaust wasn’t smokey at all, at least at highway speeds with light to moderately heavy throttle application.

​

I will be looking into getting compression tests as well as engine leak tests done soon (once I get some time off work) so we can get this problem diagnosed and sorted once and for all (hopefully).


Cheers,
Mo420
​

 

[190]

We do mostly urban driving, and I’ve noticed the temperature gauge points around 90 to 100 degrees whilst driving in the city and more towards 80 to 90 degrees whilst cruising on the highway. I should think that 5w-50 is pretty much spot on don’t you think?

If your engine is running hotter than another one that's using 40 grade oil then your engine will be seeing a similar viscosity running on 50. The difference in temperature to make a 50 grade look the same as a 40 grade isn't much. I'd have to look it up but it's probably only 10-15 deg. C. So if the temperature is getting to 100 Deg C then that just about justifies a 50 grade oil but not really below. To be honest a 40 grade oil is good for 100 Deg C too. If you'd said the engine always runs at 100 Deg C or above then the 50 grade oil would be more justified. If modern cars had an oil pressure gauge there would be no need for debate because as long as it made at least 10 psi per 1000 rpm then the oil grade is OK.

I’ve read elsewhere in this forum and also other MB forums that the M112and M113 engines are quite prone to sludging issues if non fully synthetic engine oil are used. Anyone care to shed a light on this?

Synthetic oil typically has a high detergent content so tends to keep an engine cleaner than mineral oil. I would definitely use synthetic.

 

[190]

This table helps to illustrate what I was saying earlier. They are not quite the grades we are talking about but it does show that for a given viscosity when the engine is hot the difference in temperature between a 30 and a 40 or a 40 and a 50 grade is in the region of 10 Deg C or even Less.

I still preferred the oil pressure gauge on my old 190e over theory as that would let you try a thinner oil and if the pressure indication was always good there would be no reason to use anything thicker.