Weird gas in oil problems (bad second tank)

[quietizkept]

Hello! There’s a lot to this, I’ll try not to ramble. I have a 1987 V10 Silverado that has an around 1996 Early Vortec GM Goodwrench crate motor short block. It has all the top end parts from the original 5.7L TBI, which I thought wouldn’t work, but here it is. Generally speaking, all the original motor parts fit on this (such as the TBI itself, and all the sensors). 3k on the motor, then it sat 20 years at least. I had one fuel tank and all the goodies replaced, new second one soon. Since I got it, the truck has intermittently given off a strong turpentine smell. It was running excellent for a few months, then it started fouling out spark plugs severely to where it wouldn’t run. Did it three times in a month, driven not even 10 miles. The LAST time they fouled out, right then, the bad tank started leaking severely from the filler cap! There was the turpentine smell. I checked the oil, and it was 4x too high on the stick! There was the turpentine smell again. Drained out that oil, and when I went to put my plugs in, I almost got one in and dropped it. I noticed that the tip where it had touched the hole was covered in that same black stinky stuff. That’s when I noticed the stains inside my TBI (pictured). The bad tank is obviously full of bad gas, could it be feeding back through the return system some way? I don’t know yet how that works. How on earth is it making more? Every time I ran it after, the filler neck filled back up and spilled out on the bad tank. This black stinky crap is everywhere, even in my crank case! Wtf? The only real modification I did was put a stronger spring in the regulator when I rebuilt the injector. That made it run horribly rich, even after I reset the ecm. Since all this, I kinda went berserk on new parts. Still waiting on some to arrive. Map sensor, egr solenoid, egr valve, o2 sensor, CTS, new distributor cap & rotor, and a big MSD coil will all be on it soon. New factory strength regulator spring inbound too. New secondary tank soon, but, until then, Should I drain out the old one? How do I do that? My tube hits something halfway down the neck. I really want to be able to drive to the shop to get my next tank. The wrecker driver out here bent up my baby twice already. Thanks for ANY insight. Many thanks from a truck noob.

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[quietizkept]

Yes I know my whole TBI looks filthy, but inside was shiny silver. This is actually the best parts from three plus a rebuild kit. The parts in the best mechanical shape were the worst looking. I scrubbed the heck out of the parts in a bucket for a week to get them to look THAT horrible lol! There are stubborn corrosion stains all over all the bare metal parts on the engine. It sat at the edge of the woods for two decades. I could clean on this truck until I die.


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[jjester6000]

Yes I know my whole TBI looks filthy, but inside was shiny silver. This is actually the best parts from three plus a rebuild kit. The parts in the best mechanical shape were the worst looking. I scrubbed the heck out of the parts in a bucket for a week to get them to look THAT horrible lol! There are stubborn corrosion stains all over all the bare metal parts on the engine. It sat at the edge of the woods for two decades. I could clean on this truck until I die.


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If I were you, I'd go to the junkyard and pick up a whole tbi unit for $20, and stick it on to see if it fixes the problem.

If it does, then it is probably something you did while trying to rebuild it (god knows I've screw up plenty of times rebuilding carburetors).

Also the bad gas thing, I'd drop the tank and check it out. It's going to be nasty after 20 years (though I have successfully ran an engine on 40 year old gas before).

 

[legopnuematic]

Was the engine run much before being parked? Sounds like a mixture of things, but running rich+poorly seating rings would certainly put gas in the oil.

I don't have any personal experience with GM's tbi, but it seems that they generally work until they don't, with the issues being too much fuel, no fuel, etc.

Check over anything you have touched, along with anything that someone in the past would have meddled with, not uncommon for a wire to not be connected fully, line routed wrong, simple things.

If the tank is nasty, just replace it. They are cheap enough that it does not make it worth the effort to try to flush it out, all the concoctions, swishing rocks, 13 fuel filters to still have a dirty tank.

The hail mary fixing can work, but often ends up with frustration, wasted money and sometimes not even correcting the issue.

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[Grit dog]

Agree, sounds like multiple issues.
Need to isolate each problem.
Tank filling up means it’s pulling from one tank and returning to the other. Likely something with the tank switching valve. Imo.

crankcase filling full of gas? Idk how it would run if 4x as high on the dipstick. How many gallons came out? That’s bad. I don’t know if it could make that much oil just with bad rings and still actually run somewhat normally or at all.
Rings, injectors, pulling fuel in through vacuum line? Idk but seems separate from tank filling issue.