Ok I purchased my 75 280z over the summer, I mostly use it for Z meets/shows, occasionally take it out on the weekend for a cruise. The problem im having is it seems to be using about a quart of oil every 300-400miles. It doesn't smoke at all, does not leak at all, so what else might be going here? Anyone have similar issues in the past? My 280z has 110K on it, I use 10W30 valvoline, should I maybe switch to high mileage oil? I've put 1k on it since this summer and today found it almost a quart low after adding a quart 150 miles ago, I took to a meet 1hr away and lost almost 1quart from that drive.

Some people tell me its 30yrs old and to be happy that losing oil is my only problem, but why am I losing any if its not leaking/smoking at all?

Thanks for any help.

Leaking and burning are the only two possibilities, although it's possible to have oil leak into the cooling system in which case you might not notice it right away. My guess is that it really is burning the oil and that it's not completely obvious. Back when my car was burning oil I really only noticed it when driving at night with another car following me. On hard acceleration I'd really see a lot of smoke in their headlights. You might want to look at your spark plugs for evidence of oil fouling.

checked the plugs today, a little carbon on them but absolutely no oil on them. its freakin me out, my only guess is either it leaks only when I drive it but I cant find any anywhere underneath or you may be right that it may burn some when I take it on the longer drives but I have seen no black smoke once neither has the Z's following me at the meets. Just seems like a lot of oil(1 quart) to lose in a small time(200miles) without smoke/leaks. I seem to lose it on the long drives, 1hr., never around town.

But thanks for the advice. sorry if you guys cant help me, I was hoping someone might say "thats normal", j/k its not, or maybe one of you found some leak underneath that may only leak when driving.

If it really is leaking only when driving you should see evidence of the leak on the engine itself. There are only so many places oil can leak from: oil pan gasket, head gasket, front cover gasket, oil pump, etc. You could always take it to a car wash for a good engine degreasing and then after it's good and clean take it out for a long drive.

I've pressure washed underneath pretty good and found no signs of leaks since its pretty clean now, I may just go with some high mileage oil or maybe heavier weight and see if it burns/leaks the oil anymore. Thanks for you advice Mike, I appreciate it.

you might want to see if it is leaking oil from the rear crankshaft oil seal. If you have oil in your transmission bellhousing, you have a leak.

IF you;re not seeing white or bluish smoke when you drive it, there's no oil in the water, and no obvioos leaks when it sits, my best guess would be the rear crank seal as well. This should be evident by a drip only when running, possibly even only at higher RPMs, dripping off the bell housing as mentioned above.