Was considering purchasing truck; 55k miles. The dealership says they changed engine oil but after 300 miles, engine oil is dirty. Dealership told me it was typical of GMC/Chevys to have dirty engine oil. My mechanic says previous owner probably didn’t change engine oil on any regular basis. Research says “probably. nothing to worry about, but …”. What say you? I did not putchase truck.
To quote Robert DeNiro, “if there is any doubt, there is no doubt”.
In other words, if you are unsure, walk away…
It’s sort of hard to believe there’s something unique about GMC/Chevy truck engines that they all have dirty oil. I’d discount that idea. First guess, the dealership says they changed the oil but didn’t. I’m not saying they were intending to mislead you, they may have just made a paperwork error. Second idea, they did change the oil, but used a synthetic. If the truck hadn’t been running synthetic oil prior, it could get dirty pretty fast with the first synthetic oil use. Synthetic oils tend to clean the engine internals of gunk better than dinosaur oils.
Well?
That’s not a Chevy. It’s an Isuzu.
And Isuzu vehicles aren’t known for their reliability history.
Tester
@Milissah-You just followed the best rule of used vehicle buying. If there is even one red flag look elsewhere because there are tons of used vehicles on the market.
@melissah
55,000 Miles On An O9 (7 or 8 years old) “Anything” Could Be Too Few Miles, Depending On How The Miles Were Accumulated And How Often It Was Changed. That Engine Could Be Loaded With Sludge, Loosened Up By The Fresh Oil.
Find one with a know history and better yet, maintenance records to go with it.
CSA
Engine oil for a typical gasoline engine of that vintage should look almost pristine after a mere 300 miles
I’m also leaning towards the engine oil was NOT changed
Whether this was an outright lie or a clerical error, who knows? :neutral:
“Dealership told me it was typical of GMC/Chevys to have dirty engine oil.”
Now that is definitely a load of . . . fill in the blank 
If they tell you such garbage, maybe they’re also being dishonest about other things, in regards to the truck
we have tons of GM trucks in our fleet . . . including some Colorados . . . and they don’t all magically have dirty oil 300 miles after the oil change
Whoever told you that is probably hoping you’re gullible, because you’re a lady . . . ?
Shame on them 
Good that you walked away . . . plenty of other trucks for you out there
Tester
That’s not a Chevy. It’s an Isuzu.
Well, maybe, sorta… from Wikipedia:
—The Chevrolet Colorado and its twin, the GMC Canyon were jointly designed by GM’s North American operations, GM’s Brazil operations, and Isuzu. Isuzu, which participated in the design process, began selling its own version worldwide in 2002.[2] In late 2005, Isuzu offered a version in North America called the Isuzu i-Series. This North American model Isuzu shared North American powertrains, styling, and equipment with the Colorado/Canyon twins and differed from Isuzu’s worldwide offering. All Chevrolet, GMC, and Isuzu versions worldwide are based on the GMT355, itself the basis for the GMT 345-based Hummer H3. Most vehicles for markets outside North America are manufactured at a GM plant in Rayong, Thailand, as well as at a GM plant in São José dos Campos, Brazil. Most North American-market vehicles were manufactured in Shreveport, Louisiana.—
The dealer obviously lied to you. Now that you know he lies, what else did he lie to you about?
Keep looking. And keep using your uncommon good sense.
Whoever told you that at the dealer is lying, clueless, or both. Not buying it was the smart move.
Ford oil used to always look clean and GM oil always looked dirty. Neither make was more reliable than the other. Used to bees don’t count much these days but dark oil isn’t a bad thing. You can trust the dealer to put the wrong weight oil in their used fleet but that’s about as far as trust goes there.
Dirty engine oil means that the oil is doing it’s job. I would worry more about pristine oil at 300 miles than dirty/brown oil. I never believe anything a dealership tells me anyway so that’s where I stand on the issue.
@missileman
"Dirty engine oil means that the oil is doing it’s job. I would worry more about pristine oil at 300 miles than dirty/brown oil."
I agree with your first sentence, but respectfully, not he second one. I would possibly be more likely to agree if it was altered a little, by adding a zero, as follows.
“I would worry more about pristine oil at 300 3,000 miles than dirty/brown oil.”
I run my cars to at least 250,000 miles. My own experience, over many years, has been that as engines (all types of ICEs) wear (or wear-out) they tend to contaminate the oil at a much greater rate and darken the oil more quickly.
Also, as I have pointed out earlier, this dirty oil could be a situation where sludge is being dissolved by fresh oil.
CSA
missileman
Dirty engine oil means that the oil is doing it’s job.
Back when I started changing oil, in the 70s, it always drained pitch black. The conventional wisdom seemed to be: Yep, this modern oil has detergents, it’s supposed to get black quickly. It’s fine.
Then, in the 90s, I began to notice the drained oil was no longer black, sometimes it was barely brown. In the 2000s I was draining oil that looked so clean I decided I must be wasting oil, and started extending my change interval. As I said on some topic the other day, my newest car, a 2014 CR-V, has an oil life monitor that calls for roughly 12K change intervals. This is with very gentle low RPM operation with no very short trips and very few restarts.
Maybe modern engines just tend to have much less blow-by than the junk from the past that hardly ever made it to 100K?
Missileman, my feeling on that is that after 3,000 miles in a 7 year old engine black might be arguably acceptable, because one of the oil’s functions is, after all, to wash the cylinders and flush the bearings, but after 300 miles? That would suggest a whole ton of blowby. I find it far more likely that the salesman simply lied.
I tend to think the oil was not changed or the vehicle had super nasty oil in it and someone did a hurry up oil change without draining it all out. Tend towards the former…
Wonder what the saleman’s reaction would be if he was asked whether or not he had ever heard of Diogenes of Sinope…
LOL, I’d heard of Diogenes, but had to look it up to remember who he was! Haven’t heard that name in… well, since I was a tot!
Diogenes is probably still looking after leaving that dealer in a hurry… 
A lot of that darkening of motor oil is just soot washed off the cylinder walls and the crevice above the top ring, where the flame front quenches.
Top rings have moved closer to the piston top over the years to reduce that pocket.
Different piston designs and cylinder wall finishes are going to result in different oil appearance.