Mysterious oil loss in 2000 Sierra

[Sierra Advocate]

After reading about the merits of synthetic motor oil, I decided to make the change to the premium stuff. I drive less than average miles so I felt I could justify the added cost. From my research, Mobil 1 5W-30 was the ticket. I looked into filters as well and went with the AC Delco UltraGuard. I changed the oil and filter myself and yes I did put in the correct (6 qts) amount. Somewhere around 4K miles later, the check oil level light came on. When I looked, it was down two quarts! We're talking about a babied 2000 Sierra w/5.3 liter engine with only 42K miles on it! It's always been driven very conservatively. There aren't, and never have been, any visible leaks. I'm stumped as to how that much oil can "disappear". Does anyone know of this sort of thing happening and if so does it have anything to do with switching over to synthetic oil?

[GMS_GMC]

I had this same problem with my 2000 GMC Sierra with a 4.8L. I was using the Mobil 1 synthetic and a Fram filter. I lost a liter in 5000 Km's. No idea why.

[Sierra Advocate]

Thanks for the reply. It's always good to hear that you aren't the only one with a perplexing problem! I have a question for you now. Had you been using the synthetic oil for some time or did the oil loss occur immediately after you changed over to it?

[GMS_GMC]

I don't really know when it happened but the oil light came on at about 5000 km's and it was down then. I'm guessing the metal in the engine absorbed it. Many metals are porous and absorb some oil. I just gave up on the sythetics for now.

[Kevcules]

Hey Guys
Sounds like you guys are using the synthetic oil too soon or too late. Mechanics say you shouldn't use this oil untill the engine is well broken in. 10 to 15 thousand miles. This oil won't allow the engine to break in properly, and most new engines burn oil untill broken in. Also , if you have too many miles and the engine is too worn , they advise not using it ,(otherwise I would use it in my 91 GMC Sierra with 185,000 Kms ) ,but try a heavier grade petroliem oil. There are some "high mileage" synthetic oils out there now , maybe try that.
So if you are sure you are not leaking the oil, change it to something else and see what happens. Sythetic oil works well. I have Mobil 1 in my Chev Venture and started using it at 40,000 Kilometres, I now have 120,000 kilometres and it doesn't burn hardly anything between oil changes.
Kevcules

[Sierra Advocate]

Thanks for the info, Kevcules! Not to discount what you said at all but I wanted it known that I changed over to the Mobil 1 oil at 37K miles. From your reply can I take the knowledge that synthetics "burn up" more than traditional oils?

[CheckEngine]

I have an '01 Sierra w/ a 5.3L engine, if I go over the recommended mileage (3,000) between oil changes, like if I let it go to 3,500 or so, my check engine oil light comes on as well & it is down a quart or so. I don't see any visible oil leaks. I just have to make sure to realigously change my oil at 3,000 miles... I don't use synthetic oil. I bought the truck with 51,000 miles & was told that if you switch to synthetic with more than 30,000 miles on your vehicle it will burn more oil & / or develop leaks... Not saying that is the case.. Just what was told to me by a mechanic at the local GM dealer.. Hope you find your lost oil, I am still looking for mine....