This is similar to this question but I'm more interested in possible long-term effects.
The story is we think my son (new driver) accidentally put diesel fuel in his 2005 5.7L Hemi engine. Luckily it was only half a tank (~10 gallons) .The next morning, the car would "start" but immediately stalled. We towed it to a repair station who did an engine diagnostic and determined that the throttle body was "dirty", and after cleaning it, the car at least ran (though a little sluggishly). They did not think it was diesel fuel and thus did not drain the tank. They thought it was just a batch of "bad gas", which surprised me since he got it from a national brand station. The fact that it ran after cleaning the throttle body makes me think that it was not diesel, but the effects all sound like what you'd get by trying to run diesel through a gas engine, so I'm not certain.
I filled it up (another 10 gallons) with premium unleaded (the manufacturer recommends 89 but I've used 87 more often than not) to try and improve the "quality" of the gas (I know this isn't how octane works but was willing to pay extra to try and reduce the effects). It still ran a little sluggishly (especially at start-up) but other than that seemed fine. Since then, I've added another 10 gallons of premium to dilute the "bad gas" further, and it is running much better now.
At this point I've either got:
- 10 gallons of diesel/bad gas (if they do not mix and the diesel is used last)
- No diesel/bad gas left (if they do not mix and the diesel is used first)
- A solution of roughly 25% diesel/gas that continues to dilute every fill-up.
So I'm more interested in what possible long-term effects of this 10 gallons of diesel/bad gas could have? What I've seen is that there should be no damage done, but the nature of diesel can gunk up spark plugs and other things. Is there anything else I should do to prevent/reduce serious damage?