Oil Turned Dark in 40 miles.

[Gasbuggy]

Friend of mine bought a car with a mild low mile small block Chevy. Inside the valve covers it's beautifully clean. While it only had 40 miles on this oil it did have many cold starts dialing in a rebuilt carb. Still though, something seems off here. The oil was Valvoline Blue 15w40 and it's 5 months old. Has a Fram Xtra Guard on it.

The prior oil change was many years old gas soaked oil but only had about 500 miles on it.

The engine doesn't smoke, though it's been driven so little, the jury is out on if it burns excessively.

 

[Jetronic]

the 500 mile old oil was dark too?

it only takes a small amount of old oil to colour the new oil.

 

[Gasbuggy]

I didn't see it but safe bet it was, and very fuel soaked. But this oil looked grey to me more than any other color.

 

[SubieRubyRoo]

Excessive heat will change an oil’s color very rapidly. Gen I SBCs are not known to be masters of mechanical efficiency. Does he have an oil temp gauge?

 

[Lubener]

I would do a short term oil change to clean things up and address the fuel dilution issue.

 

[Jetronic]

I would do a short term oil change to clean things up and address the fuel dilution issue.

I would too.

 

[cdlamb]

It is hard to tell by color only.

You say fuel dilution? Are you just going from smell? I always smell a gasoline odor in my oil, but rarely see fuel dilutuion at severe levels. & by smell I can't determine if one sample was worse than a previous until I get results back.

Drive it for half an hour or longer trip, with high way driving to get it up to full operating temp. Send a sample. Drain the oil & refill if you feel its bothering you. I only pay about $28.00, so its not a crazy charge. I would not use Blackstone! I have found they are inconsistent when comparing sample sent to them compared to a 2nd lab. Always underestimate fuel dilution, & want to run the additive pack for a longer length of time. Find a lab that uses gas chromatography.


Color is hard to determine on the paper towel. It will always look dark to me.

I feel that turbo motors seem to turn the oil darker - more quickly.

 

[ATex7239]

Fuel is a really good cleaner. Probably all gunked up from cleaning the engine.

Just did an old change on my daughter’s +200K mile Hyundai. Only 600 miles and 6 months on VL blend but all short trips. Oil was black and smelled of fuel.

Don’t underestimate what fuel dilution and short trips can do.

 

[joekingcorvette]

I would do another drain and fill as others have stated and see if it looks better. Maybe even replace the filter.

 

[atikovi]

Friend of mine bought a car with a mild low mile small block Chevy.

Would that be the diesel 350 from the 70's or 80's?

 

[Hermann]

I didn't see it but safe bet it was, and very fuel soaked. But this oil looked grey to me more than any other color.

I saw tinges of green on that paper towel.

 

[930.engineering]

.
Congrats, apparently you got a Diesel engine!


Many engines keep a quarter of old oil during oil change.
Or your mechanic tend to cheat you . . . .
.

 

[someonesomewhere]

.
Congrats, apparently you got a Diesel engine!


Many engines keep a quarter of old oil during oil change.
Or your mechanic tend to cheat you . . . .
.

Never seen a diesel with a carb, though...

 

[Gasbuggy]

Would that be the diesel 350 from the 70's or 80's?

no no, 327.

 

[Gasbuggy]

I would do a short term oil change to clean things up and address the fuel dilution issue.

That's what went on here, the carb seems to be leaned out well enough now.

 

[Gasbuggy]

Excessive heat will change an oil’s color very rapidly. Gen I SBCs are not known to be masters of mechanical efficiency. Does he have an oil temp gauge?

Interesting thought. My other concern was the oil pan was on and off recently, but no one alive that knows why. No oil temp gauge but 160 degree stat in the engine barely gets up to 155 degrees. A 180 is on the way.

 

[Gasbuggy]

I saw tinges of green on that paper towel.

Well, it's not Brad Penn. Maybe a prior change had some dye in it to find an oil leak.

 

[SubieRubyRoo]

Interesting thought. My other concern was the oil pan was on and off recently, but no one alive that knows why. No oil temp gauge but 160 degree stat in the engine barely gets up to 155 degrees. A 180 is on the way.

Older engines that don’t have an oil cooler generally have no relation between coolant and oil temps.

Besides, the oil temp gauge only gives you “best case” scenario- the average oil temp in the sump. The oil temp in the bearings and on the cylinder walls will be significantly higher; I forget the rule of thumb to approximate sump temp to “work area” temp. But it’s significant; if you seem 250+ in the sump, the bearings are likely easily 350*+.

Overall, color doesn’t affect protection or performance; chalk it up to various factors, but get a gauge to make sure it’s not excessively hot, which would thin the oil and maybe get to an area of concern.

 

[subyski]

Some HDEO turn dark relatively quickly and combined with fuel, this could explain what you are seeing. Once the Carb is dialed in better, do a change and see if the same thing happens.