My motor had maybe 2k on it when it started knocking and lost oil pressure. I tore it down and noticed that the oil was as thin as water. I had a spun rod bearing and I noticed on all the bearings that the center of them was messed up. I drove 2 miles on no oil pressure. With a good oil I wouldn't think it would of messed the bearings up the way it did. I stuck my finger in the oil and I could pick up a faint gas smell. I've been sick so its hard to smell anything. I could tell the thin oil and my rpms made the bearing spin. But why gas in my oil? I don't want to do the same mistake again and trash another motor. I did have a race a few weeks before where I sprayed a 200 wet shot. It does have correct jets. My cam is a 106 lsa which is not good for nitrous. I think spraying it slowed me down. Is it possible that with that cam and that much nitrous I sprayed fuel around my rings and after gas sitting in my motor broke down my oil? Any help would be great, thanks! Stock motor just h/c car.

 

Older vehicles used to experience this when the diaphram ruptured in the manual fuel pump but i don't think that is possible now. Newer cars have electric in-tank fuel pumps. Probably something injector related.

 

that is incorrect, this information is continuously regurgitated in the boating world where many motors still use mechanical fuel pumps and it pisses me off. When a mechanical fuel pump diaphram gets a tear in it, ruptures or whatever you want to call it, that mechanical fuel pump cannot pump fuel anymore because with the hole in the diaphram there is equalized pressure on both sides of it now. All that will happen is as the diaphram moves up and down as the engine continues to run for a brief moment afterward, it'll slosh the fuel around within the fuel pump and that volume of space is maybe around 5 ounces. the pump cannot pump fuel anywhere at this point, so all you're dealing with is whatever fuel the pump has below the diapram, which is very little. Most of that fuel as it passes through the tear in the diaphram will then leak out the vent hole in the pump body before it ever enters the crankcase. And on top of it, the fuel pump pump arm shaft is in a bushing (much like your intake/exhaust valves in the head ride in valve guides or bushings) and fuel will not leak past that into the crankcase very much if at all. If it could, then oil would leak out from the crankcase into the upper half of the pump body.

if you were running 5w30 oil then that is one problem. The viscosity of 5w-30 at operating temperature of 200-250 deg F is at the minimum for reliable wear protection. this is ok for normal cars which is very rare to have any fuel dilution, but when fuel dilution does happen then it doesn't need to be much for the oil to lose enough viscosity to damage bearings especially if the engine runs hot. Couple that with racing and nitrous usage, and it just increases the likelihood of damage. If you have done computer reprogramming then that is a likely the source of the extra fuel. Another possible source is a leaky injector such as after shutdown. And if the motor is running overly rich all the time, and only sees 1/4 mile passes and 2 minutes of runtime then all that gas will build up in the oil and not burn off. For protection I would run an oil with a viscosity of 40 at a minimum, and if you know you'll be getting fuel dilution then using a 20w-50 oil can help guard against that somewhat but is a bandaid fix. The best thing to do of course is check the oil routinely. If you have a sample of engine oil now from the failure then sending it out for oil analysis can be helpful in telling you the % of fuel dilution.

 

It sounds like to me that you might of had a extreme rich condition and the engine was not burning all the fuel which in turn mixed with the oil. Is there any scarring on the cylinder walls? That is the only other way you could get gas in the oil. EDIT: Yeah what he said lol. I didn't read the post above.

 

how do the rings look ? also was the engine at full operating temperature when you sprayed it ?