Bought the envoy w/ 70,000 miles, fresh oil change. @ 74,000 miles it was 1.5 qrts low, put in 5w30, checked oil 2 weeks later it was 1 qrt low. do not see smoke or any leaking.

Looks like the 6 cyl calls for 5w30. I wouldn't go that thick (10w40). If anything maybe 10w30 in the summer.

You did not mention the year make and model, but unless it is a diesel I doubt the weight of oil would do it.
I would take it back as quick as possible before it locks up.
You have checked to make sure the oil level is full, right ?

first thing on a turbo, do an oil change using full synthetic oil. If you can, plan on replacing plugs and plug wires, replace antifreeze, and check brake linings. VW Beetles are tough to work on (little room), and it would also be a good idea to check hoses and belts, cleaning the engine.

From empty it takes approx 5 qrts plus filter.The filter will take a half a qrt + or - .You never want to start a car with a dry filter.It is a habit that made perfect sense to me as I grew up.

If you have a vacuum modulator on the trans,it could have a bad diaphram and **** trans fluid into the engine.
Now I do not know what model or unit trans you have. No vacuum mod,then the dealer is correct.
You can look just above the trans oil pan, near the rear, for that part and easily change yourself. Get at auto parts store. It will be the thing with a 3/16 vacuum hose on it,going to a port or vacuum switch on intake manifold

If you see no leaks,, you could possibly have any one of the vacuum hoses incorrect ,, check those first as it will make the motor push out the oil, and soon will damage any gaskets in that area

hard answer most cars start using oil about 100,000
but not that much about a qt every oil change
fill you engine with the rignt amount of oil then in a week check it again... if you are low you have a problem ( if you have a pcv in that car have it changed if not there should be a crankcase purge to the air ram system have that checked if that fails you definitly have a piston oil ring that is bad
try using some lucas oil stabliser will help a lot..
you can get it at autozone i believe

I replaced my tire at 75,000 miles. I put on Goodyear top of the line tires with a 70,000 mile warantee. They were very stiff and ride harder. I wish that I would have stayed with the original tires that on it. I think GM got that one right!
Be careful what you put on it, if you like the original ride...

My sons 01 Aurora kept saying low oil, but there was no leak and we had the oil changed the day before. After looking in the owners manual, this car takes 7 1/2 quarts of oil when you change the oil and put in a new oil filter. The mechanic claimed he put 5 quarts in and checked it but he couldn't of. Over a week and hundreds of miles later the oil hasn't dropped at all!

most automobiles requires a min of 4 qrts so start there check your dip stick to see if any more is required most bmw's take 5-6 qrt's as far as type its your choice weight depends the sticker located under the hood or by the hood latch should tell you if it is missing i recomend 10w30 depends on temp.if cold 10w30 if warm-hot 10w40.most new auto's after 2000 requires5w oil but im suer yours does not hope this helps