[Niteryder]

I notice that I usually need to add an additional quart of oil in between oil changes to our 2002 Envoy. I can't see any leaks, spots on the garage floor, nor does the exhaust have any color/smell to it.

I also only use Mobile 1 full synthetic 5w30 oil with Mobile 1 filter. Any ideas? Should I try moving to a different non-synthetic oil? Or, is this just a typical trait of a high-mileage (105,000) Envoy.

 

[ylab]

More thank likely you have a slow leak at the valve cover gasket round the spark plugs. That's the most common place for the 4.2 to develop a leak, the oils then fills the valley around the plug and some will seep into the combustion chamber. The I6 has very tight tolerances and they aren't known for burning any oil.

This assumes of course that you're following the OLM and not Mobil1's 25,000 change interval, any motor is going to use some oil after 12,000 or so miles. Do you know how many miles you travel before needed to add that quart of oil?

 

[Niteryder]

I add a little every so often, but it's mostly 2,500 -3,000 miles into the oil change. I usually change oil every 5,000 miles.

 

[rbarrios]

are you measuring the amount of oil that comes out when you change oil?
Dont forget the oil filter can absorb some oil.
Also some oil is left in the knooks and crannies of the block.

That being said....
I change my oil (regular dino oil) every 10,500 to 11,500 miles (when OLM comes on).
I measure the oil that comes out.
On average I remove about 6-6.5 quarts of oil- with never adding any make up oil.
Im now nearing 147,500 miles.

 

[wardak33]

Dont forget the oil filter can absorb some oil.
Also some oil is left in the knooks and crannies of the block.

Very good point. The Filter alone can hold up to half a quart IIRC