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