Whats up fellas, my dad has a 2001 Sierra C3 with 49k miles. Never abused, etc...anyways I changed the oil about a month ago in it. Today after washing I checked it and it was about 2.5 quarts low. I figured maybe it was a mishap since I had the truck running earlier. I let it sit all day, and checked again and it only had a tad bit more on the stick. Now, the truck has been getting very poor fuel milage lately. He gets around 230 miles per tank where as I am getting close to 300 with my Denali with 4.10s. His used to get about 310/tank. We are wondering what the problem might be...any ideas? Could the oil consumption/fuel economy be related? Any info is appreciated.

 

Usually too much oil in the combustion chambers will make it not burn as well.

 

Do you ever see blue smoke coming out of the exhaust pipe? The pcv valve could be the culprit.

 

Nah never any blue smoke it runs perfectly. My dad mentioned the PCV valve also.

 

That is weird. Hopefully you get the problem solved. Is it blowing white smoke out the exhaust? Obviously the oil is being burnt out somehow. If you see white smoke out the exhaust it's oil burning if it's black it's gas. Hope you get it working. 230 to the tank sucks.

 

For the gas mileage i'd try some normal maintenance stuff, like changing the fuel filter and running some injector cleaner or intake cleaner, if you haven't already.

 

Is the truck bone stock?

 

My '00 4.3 truck had a similar problem later in it's life, up around 85K+ miles. The thing was a DOG - especially on the highway... it couldn't hold 70mph up the mild hills here in Massachusetts. (you'd step on the gas, and you'd slow down until you downshifted to 3rd).

I don't recall how much oil I was burning, but it was more than a quart a oil change. I never saw any evidence of where it was going. Plugs were clean(ish), and there was never any smoke out the exhaust. My gas mileage was horrible - around 12-13mpg.

Right around 95K miles the motor gave me a huge, HUGE fit... I started it up one 0*F night up North, and I thought a rod was going to come through the block - I've never heard an engine make a noise that loud and live. It rapped for about 30 seconds and it just went away. It sounded like someone with a medium sized ball-peen hammer wacking the side of the engine block. I took that as a sign the motor was real tired, and I got rid of the truck shortly after that.

The motor was one of those that always ticked it's whole life. The only thing I had done to it was a K&N drop-in filter, and a Borla cat-back. Looking back, there is the possibility that I over oiled the K&N, mucking up the MAF, and throwing off my gas mileage and highway power... but I can't say for sure now.

I used Mobil1 5w30 and usually Fram filters for about 90 of those 95K miles. I now understand thing thing about Fram filters, but I'm also very leery about M1 now too.

The truck was very well maintained otherwise, which really rubbed this problem in my face. FI cleaner, fuel filters, etc. - they were all done.

Sorry I can't give you any real help...

Maybe you could pull an oil sample, and send it off to be analyzed? (what is it, about $20-30?) I have the contact info in my PM's if you want it?

 

If you still have the original style plunger and spring PCV valve, that could be your culprit. There is a re-designed fixed orifice PCV valve that's supposed to help oil consumption issues.

Pull the hose off the PCV and check for the presence of oil. Shake and examine the valve, if it has a plunger and a large hole at the bottom, it's the original style. The re-designed valve is empty with a tiny hole at the bottom.

If this seems like it's your problem, I'd also recommend getting an oil catch can, if you do a search you'll find numerous threads about it. You might want to try doing a top end clean service on the engine also. GM Top End Cleaner and SeaFoam are both good products.

 

http://pistonslap.com/ .I HAVE THE SAME PROBLEM .