I recently changed the oil in my '86 560SL to Mobile 1, and just returned from a 3 day road trip. What happened was this. We got stuck in a lineup to cross the US/Canada border, barely moving for over 30 - 40 minutes, bumper-to-bumper. The temperature guage for the engine never really registered anything seriously high, just hot. The guage was reading just up from the mark between 80° and 120° Celcius. The dash ambient air temp was reading over 95°.

About halfway through this ordeal, LOTS of blue smoke came pouring out the tailpipe, a real cloud, easily seen in the rearview mirrors. I kept the transmission in neutral as much of the wait as I could, and occasionally revved up to 10,000 in an attempt to get the fan to cool things down a bit. The smoke persisted, even while city driving right after we got going again.

After we stopped and had lunch, letting it cool off, there was no smoke on restart. I checked the oil level and didn't see any drop, nor was there any obvious oil in the engine bay (but then the blue smoke came from inside the motor, not outside, so this was expected). I didn't see any smoke during the rest of our trip, but we didn't get stuck in traffic in unbearable heat again either.

This is the first engine I've owned with synthetic oil, 10W30 Mobile1, and the first time I've experienced this one-time-only blue smoke phenomenon. I have a 1985 380SE with the M116 engine, and I changed the valve stem seals to cure a persistent smoking problem on it.

What could have caused the blue smoke in this case? My thoughts are that the cylinder walls might have expanded enough in the heat to allow oil to get by the oil ring(s) on one or more cylinders, or that one or more valve stem seals are weak and temporarily allowed seepage into the cylinder(s). Or is this a peculiarity of synthetic oil in an older engine (180,000 miles BTW)?

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1986 560SL
2002 Toyota Camry
1993 Lexus

10,000 rpm would blow the motor right through the hood. I'm hoping you meant 1,000 rpm.

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Question Authority before it Questions you.

.yes, typo there. And revving didn't help either.

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1986 560SL
2002 Toyota Camry
1993 Lexus

It does not take very much oil to make smoke. Synthetic oil does have some detergent qualities and if you just changed to synthetic you might have loosened up some varnish and stuff that was sealing around the valve stems and now it is leaking a little. I would say if, under normal driving you do not see smoke then just forget it happened. I think though, if you look closely you will see smoke now - especially if you look out the back at night with headlights from behind. Still, if the car runs OK and the smoke is minimal it probably won't do any harm to just keep driving it.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Don: I think your car runs too hot and your cooling system could stand some improvement. Down here in Florida, we have to deal with those kind of temperatures every day for months on end. (How many days is it to late October?) Neither of my cars gets anywhere near 100 degrees (which is what you seem to have been seeing) under any circumstances, and I would be very unsettled if they did.

I redid the entire cooling system, down to the block drains, in both cars. The 380 is particularly impressive, generally staying right at 80, and only climbing above that if we lose airflow or drive at supra-legal speeds for extended periods. Even then, I haven't seen more than 88-89, and that didn't last long. Part of the reason for that performance is a 75-degree thermostat, which you may not be able to obtain for a 560. In my experience, observed temperatures seem to be 4-5 degrees higher than the figure specified on the thermostat. Thus, the 84-degree t-stat puts us close to 90 under normal conditions, and close to 100 when the heat is really on (and also for a period during warm-up before the t-stat opens fully). Since M-B refers throughout the service literature to a normal operating temperature of 80 degrees, I find the 84-degree thermostats wholly unacceptable in this climate.

Secondly, and at the risk of reigniting yet another oil debate, why would you want to run 10-30 in an M117, especially in the summer? Per the owner's manual, 10-30 is only appropriate up to 86 degrees F ambient. (I made the same mistake myself years ago when I didn't know any better. But at least I always, always changed my oil hot and often!) You should be running 15-40 or, if you've been following the ZDDP discussions, a 20-50 like Brad Penn or Valvoline VR1. Our engines are different from the newer M-B offerings and should not be fed the same diet.

At 180,000 it is possible that your valve stem seals are getting tired. My 380's were done at 232,000, by which point the smoke upon launch was becoming embarrassing. But there had been a little smoke for a long time before that. How much oil are you using between changes?

Keeping your temps down and switching to a thicker oil will probably be sufficient remedies for quite a while. But your car was trying to tell you something; it is our job to listen! And these cars are most emphatically worth listening to, aren't they?

My only input on this is that you need a heavier oil, I'm too lazy to add more.

15/40. 15/50. 20/50. 10/60. etc.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

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