Unleaded in diesel truck
About 10 days ago, I accidentally put less than half
a gallon of gas into my diesel truck (2008 f250), I
topped it off with about 18 gallons of diesel. So far
my truck seems to be running fine, will my truck
still be ok? Did the gas already dilute or burn?
I’ve also driven it close to 500 miles
You should be fine, that small amount of gasoline mixed with what was still in the tank and what you added in on top of that really diluted the gas. I wouldn’t worry about it.
Gasoline in a diesel system is destructive in any amount over about 10% of the tank. Immediately, the gasoline will float and not enter the system, but in a short time it will be absorbed throughout the diesel fuel. This can cause pre-ignition which can lead to engine damage. Gasoline contamination can also damage the fuel pump and the diesel injectors, and as gasoline is a solvent it can corrode the entire system. BUT, a half gallon in 20, you should be OK. But I'd top off the tank each time it's half empty for a while.
You are in luck as diesel fuel is heavier (~7.1 lbs. per gallon) than unleaded fuel (~6.2 lbs. per gallon). So you are not having any issues as the unleaded fuel is floating on the diesel fuel in the tank. If you want to be absolutely sure you will not have any issues in the future, you really should have the tank completely drained. If the fuel level gets low, it may pick up some unleaded and send it to the engine (which would be bad).
You dodged the bullet this time. I would top it off with diesel to keep the gasoline diluted.