M42 knocking sound

[LivingLegend06]

OK, so my m42 has just recently developed a fairly loud knocking sound that is proportional to engine speed. The motor has 142,000 miles. I'm running royal purple full synthetic 10w30 that has just a touch over 2000 miles on it.

I think the problem may have come from this last weekend. I went on a fishing trip and on the way back i decided that i would be able to get away with using the extra gas that we didn't put in the boat to fill my car. I put 6 gallons of regular into my tank that was a little less than half full(premium). I've always used premium and when I was running the regular/premium mix (close to half and half i would expect) it seemed to studder slightly in higher rpms under heavy throttle (i noticed it best in 4th gear around 80mph), I didn't think much of it at the time but this is the only thing that I have to suspect.

Is this rod knock, am I fucked?

The Sound:

[NOMAD]

could be. Did you hear any "tiny rattling" noises when on the gas? The car needs 91 octane to survive the higher compression (and add to that the carbon deposits). If it is loud it could be the piston slap, or a spun rod bearing. If it's not so loud maybe it is a valve issue or something in the head.

Bad boat gas is probably a far cry from good high octane, especially at high rpm and WOT like you seem to have been doing.

Hope it's not bad news

[LivingLegend06]

This "boat gas" that I refer to is just regular that was pumped into a plastic gas can 3 days before I put it into my car, nothing out of the ordinary except for the fact that I used regular instead of premium (I was in an unfimilar area a long way from a gas station so instead of getting lost with an dwindling supply of fuel I used what we had on hand figured it would be okay once)

My drive back have a good hour of mountain driving so I was enjoying the back roads and passing required me to have to get on it pretty good. I didn't hear any pinging or any sings of detonation, but my ear is not trained for this kind of thing either.

The sound is loud enough to be heard below 45mph for the most part. Above that I cant really tell the difference from before it started making this sound. Its hard to tell from just standing over the engine but it seems like its coming from the bottom end.

I need this engine to at least make it until the end of this school year. Anything I can do to nurse this thing along and drag out its life (thicker oil or something?)