All

The following is going to be long and involved but I wanted to impart as much information as possible in order to paint a clear picture of the symptoms and circumstances. Over the last couple of days I had replaced most of the fuel lines and some vacuum lines under the bonnet (hood) of my '71 280SE 3.5 (M116.980 engine). In addition I had just received all 8 injectors back from having an ASNU clean and service (highly recommended before you buy new ones - if you can get then) which I duly refitted along with fresh injector seals. Doing the injectors was actually the original impetuous to do the job as some of the short hose connections from the fuel rails actually had blisters on them - 35 year old rubber and all that. Suffice to say that everything went back together nicely and the car, once warm, ran a treat and definitely felt like it was pulling even better than usual.

Now for the bad bit. I took it out for a spin to warm it through on Saturday (I have the classic hunting problem on a cold start - but that's a different story and one than can wait till later - I have a plan) and basically got caught behind a van doing about 50 mph on our motorway (limit 70mph) , the engine was now warm and I pulled out to over take - without mashing the throttle I might add, and happened to still be looking in the rear view when I see this massive blue/white cloud appear behind me - my first reaction was oh ***** !! I nursed her back to our house and parked her up for a think. I should add here that, as a matter of habit, I checked the oil the previous day when doing to fuel line work and it was spot on half way between the marks on the dip stick. I am also not aware that the car has ever burned any oil, but then I have only done about 2500 miles on her (Scotland is a summer only venue for these cars due to weather and road salt).

After calming down, I decided to try and narrow down the options. My first thought was of course a blown head gasket. I did the basics and checked the radiator for oil - none. I checked the oil filler cap for emulsified oil as well as the rocker cover breather on the right side bank - again none. I'm not yet totally familiar with the M116 but I suppose it could have ruptured through an oil way to the head into a cylinder - but that would be a head off diagnosis anyway I think. At this point I dipped the oil again - just over the bottom of the stick - not the minimum mark, the bottom of the stick - bl**dy hell ! That has to be way over a litre (quart ?) of oil in about 100 miles so what ever it is, it’s bad.

I though then, ok, maybe the rings are shot BUT as I said this is a new phenomenon and I am fairly paranoid about exhaust smoke. Surely rings is a wear issue and it would be a gradual 'getting worse' issue rather than the instant result viewed in the mirror, unless one or more broke of course. By the way she sounds fine, no rattles, thumps or hideous scrapping noises..

My other thought was valve stem seals. Again I don't even know what they look like on the M116 yet but I have my reasons. Obviously when I saw the oil consumption I was on here (the forum) in a flash searching for similar symptoms. All the blown gasket stuff I could find (though I may be just crap at searching on here) related to coolant loss and I also could not find a catastrophic ring failure. I did find some really weird and wonderful stuff - leaking brake servo (booster) allowing fluid along the vacuum line into the intake etc but that would not account for the oil loss and the brake fluid level is fine.

One post that caught my eye regarding valve stem seals was by Tomguy (I think) because he had an interesting theory regarding the angle the car was parked at. My drive is a fairly steep slope and I have noticed that (since the smokescreen incident) when cold, if I start her up there is no smoke what so ever for about the first 10 seconds, then a slowly increasing light blue haze develops into the belching. Logically using Tomguy's theory, the oil is draining away from the cam box area via the rear oil drain (car parked 'nose up' at about 15-20 degrees), when fired up we have to wait for the oil to circulate to the top end in sufficient quantity before seeing the smoke - it's a really tempting theory as I'm willing to do all the valve seals in preference to a full top end off job any day.

The thing that's really getting me however is the volume of the oil loss, I mean a full litre in 100 miles or less is massive. Surely a valve stem seal is not going to pass that volume ? Or is the 'sucking' of the piston maybe helping it drink ? Another point is that I pulled all 8 plugs, absolutely no oil on them at all. They all looked pretty good too - I was expecting pure black soot at least form a D' Jetronic car but they were all grey/brown though perhaps a little light (which is getting on for lean which would be frankly bizarre - but again let's not get into that now). It's therefore tempting to think that the stem seal on an exhaust is shot, allowing oil into the exhaust stream but not the cylinder, hence the clean plugs - but again, over to you far more experienced 'old timers' on here to shoot that one down (gentlemen - you may take 'old timers' as the compliment it was intended to be).

So there you go….that's all the info I can think of to be relevant but I am open to suggestions and am particularly interested in similar experiences. I know you guys are more familiar with the M117 but that's only really a stroked version of the M116 so symptoms should be identical?

Your thoughts ?

Cheers

Alan