85 740t burns oil below 1500rpm and at idle
 

hello everyone, new here on the forums and was wondering if anyone could give me and idea. today I proceeded to cut the exhaust off before the cat and straight pipe it. when the job was complete and the car warmed up it blew steady blueish white smoke from the exhaust. (didn't happen on warm up but while car is idling when warm) smells like really burnt oil and rubber. car runs good not boost lost, still pulls strong with 235k.

I have a few ideas from some other threads but no of the situations were exactly like mine.. i appreciate any and all advice.

did it smoke before you removed the cat? was the cat you pulled oil fouled ?

it only happened once before when i had the rest of the exhaust on. and i didnt check to see if the cat was oil fouled but ill take a look at let you kno

What viscosity oil are you running?

im not sure the oil was changed by the previous owner. im gonna chonge in the next 200 miles or so. but what would that have to do with it?

iirc, smoking at idle is a sign of worn valve guides more than rings/cylinders. a definative test woudl be if it smokes a lot going down a hill at speed with your foot off the throttle and downshiftedd so you're getting significant engine braking.

oh, if this is a turbo, there's another possibility, the turbo itself could be leaking oil into the exhaust out its bearings.

Yeah, w/ your mileage, it's a crap shoot whether it is the motor or the turbo allowing oil into the combustion chamber. A compression test is in order. I asked about the oil because when turbos get worn seals, they can spew oil. Along with with worn seals, passages can get coked with old oil residue. Often, experimenting with different viscosity oils can make a big difference. I had a worn T3 on my 84 760 that smoked in a similar fashion after my first oil change. I had switched to 20W-30 Castrol GTX, an oil I've run for decades in 4 cylinder motors w/ success. Switched back to 10W-30 and the smoking all but stopped. Worth a shot...

isn't 10w30 the 'normal' oil to run in these things at most moderate temperature ranges?

I know my OLDER 4-cyl cars liked 20W50, as does my bike, but the Volvos I've always thought prefered 10w30.

Alright ill give changin my oil a shot.. but was wondering if i had a bad spark plug would it do the same thing?

if the turbo bearing was leaking wouldn't it burn a steady trail of oil?

doesn't it? you said it blows blue smoke when warmed up at idle. only way to know if its smoking on the road is to follow behind it and even then, a small stream of smoke might not be that obvious.

if the turbo bearing was leaking wouldn't it burn a steady trail of oil?

mebee when you have negative vacuum a small spray of oil on the cold side into the fresh air will burn in the engine and make smoke but when there's some boost, it might not leak as much?

My turbo is in rough shape and I never see smoke.

do you have a cat? maybe its burning in the cat? (eventually fouling it)