Duramax 6600 LBZ:Black Oil, 11.3 MPG??

[E G T]

I have an 06 GMC 2500HD, CC, long bed, 4X4, Allison trans. I put on 1250 miles before hooking on to a trailer weighing 6000 lbs. MPG was 13.4 mixed driving. I changed oil and filter. The oil that was drained was clean, golden brown in color. I started from California my MPG droped to 12.5, I checked oil level at each fuel stop. It was full and color golden brown. When I got to Nebraska the service engine light came on. I drove to the nearest GMC dealer about 60 miles. My MPG had droped to 11.3 and the oil was black. They checked out the computer and said that the EGR valve had probably stuck open. They test drove it and said everything was normal. They said they would change the EGR valve but they did not have one in stock. They suggested I continue my trip home to PA. and have the local dealer check it out. They said it would not be a problem, except for the poor MPG, if the service engine light came on again. So I continued my trip. After about an hour of driving the light came on again. Oil press. was about 60 psi. at 70 MPH, water temp. 205, trans. temp. 160. I let the engine cool at each fuel stop, the light would reset and I would continue to drive. I got home to PA and went to the dealer. they checked out the engine and said the computer was not talking properly to the components and order a new one. GM would not send a new computer for the truck. They had the dealer run more tests and had them reprogram the EGR control. The service engine light has not come back on since this. I changed the oil and filter and after 300 miles it is black again. I've put on about 800 miles mixed driving no trailers and the MPG is still 11.3. What is wrong???????????????? HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[More Power]

The problem could be due to a defective EGR valve.

I've only seen black or dark oil in a Duramax on two occasions. The first time, the truck was running at or above 22,000-lbs GCW and was pushed hard for many-many miles. The second was due to excessive overfueling while using an aftermarket power module designed for the track.

Back in the mod 80's I test drove a Chevy pickup with a 6.2L diesel that had a defective (stuck open) EGR valve. It would produce voluminous quantities of black smoke when accelerating under full power. The oil was also opaque black.

If your oil becomes black I would also suspect the truck produces excessive black smoke.

There are a number of diagnostic procedures that allow testing the EGR (actual position, opening/closing), and the troublecodes are designed to allow more specific troubleshooting.

I might also want to know whether the turbo system is producing typical boost pressures. A turbo not producing normal boost pressures will allow the engine to smoke more, which could add to the soot load in the oil.

Jim

[jjcsnlynn]

I've had many diesels over the years (VW & Chevy) and the oil ALWAYS was black shortly after an oil change and expecially when draining.

Are you saying the oil should not get black in a 6600? I just purchased an 04 w/6600 in it and when I changed the oil it was 'what I thought" was the usual black in color.

Do I have a problem? EGR? There was a sticker in the window from a Penzoil change station and the truck was only 500 miles overdue for an oil change.

[Mark Rinker]

I haved owned two 2006 LBZs and put on a total of >250K miles on them. Oil was always black on both trucks, before and immediately after changing.

Loaded flatbed towing averages around 10-12mpg, unloaded empty 16-18mpg.

What codes were being set?

[jjcsnlynn]

I don't know if I have any codes. I'll scan it this week. I was commenting on the post below that the oil only gets black if there is a problem. My 87 chevy diesel used to get black, my TDIs get black and I my LB7 was black.

I guess I'm good to go.

[Mark Rinker]

I have an 06 GMC 2500HD, CC, long bed, 4X4, Allison trans. I put on 1250 miles before hooking on to a trailer weighing 6000 lbs. MPG was 13.4 mixed driving. I changed oil and filter. The oil that was drained was clean, golden brown in color. I started from California my MPG droped to 12.5, I checked oil level at each fuel stop. It was full and color golden brown. When I got to Nebraska the service engine light came on. I drove to the nearest GMC dealer about 60 miles. My MPG had droped to 11.3 and the oil was black. They checked out the computer and said that the EGR valve had probably stuck open. They test drove it and said everything was normal. They said they would change the EGR valve but they did not have one in stock. They suggested I continue my trip home to PA. and have the local dealer check it out. They said it would not be a problem, except for the poor MPG, if the service engine light came on again. So I continued my trip. After about an hour of driving the light came on again. Oil press. was about 60 psi. at 70 MPH, water temp. 205, trans. temp. 160. I let the engine cool at each fuel stop, the light would reset and I would continue to drive. I got home to PA and went to the dealer. they checked out the engine and said the computer was not talking properly to the components and order a new one. GM would not send a new computer for the truck. They had the dealer run more tests and had them reprogram the EGR control. The service engine light has not come back on since this. I changed the oil and filter and after 300 miles it is black again. I've put on about 800 miles mixed driving no trailers and the MPG is still 11.3. What is wrong???????????????? HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!


What codes were being set?

EGR equipped trucks soot up the oil pretty fast. I wouldn't spend much time worrying about oil color as a sign of engine health. Your low unloaded mileage is out of range, however. The rest of the mileage measurements sound normal, actually GOOD considering 6K# towing @ 70mph. Anything above ~60mph is going to start hurting loaded mileage potential. Add a headwind to that, and you can get some pretty ugly low numbers!

How many miles on your truck? Do you run any fuel additives?