A Wow, you have been through the ringer over the past six years! Chasing a pesky oil leak can be a real pain. You could be trying to fix what isn't the real leak. I'm slightly disturbed by your engine builder's statement that sometimes big-block Chevys just leak in that spot! I've been building big-blocks Chevys for 35 years and I've never had one I couldn't seal up. After all the parts you and your engine builder have thrown at this thing, let's look a little further.
Unfortunately, I'm going to suggest you pull the engine out of the car. First of all, you will be able to put the engine on a stand and turn it upside down. This will allow you to really clean the pan rail and ensure that you get a good seal with the pan gasket.
Yes, the silicone one-piece oil pan gaskets are great. The Milodon oil pan is high-quality. Milodon features new pan rails on its fabricated pans to ensure leak-free operation. What I would like for you to try is to pull the engine and install it on an engine stand. Do not remove the pan just yet. Run the oil pump with a priming tool to create oil pressure, just like the engine is running. If you don't have a priming tool, check out Milodon PN 23000; it has the proper reproduction of the bottom of a distributor to feed the oil through all the oil galleys. Remove the flexplate and have a buddy run the pump primer so you can watch the rear of the engine. Rotate the crankshaft 90 degrees about every minute to change the way the oil is fed to the rear main.
Back in the day, when I was a line mechanic at a Chevy dealership, I found a small-block that leaked oil through the block casting at one of the main galleys. It only leaked while the engine was running, and it looked like the pan or the rear main. After replacing the pan gasket, and the rear main seal, I couldn't get it to stop leaking. I removed the transmission and the flexplate and drove the oil pump with a primer. The oil galley that fed the rear main bearing had porosity in the casting, and the oil sweated through the block under pressure. This took me several days of work to find it, and then I had to replace the block.Source: milodon.com
Chasing Your Tail
Q I read your column every month and like the way you provide detailed, down-to-earth answers to problems. I hope you can help me with mine. I have owned, since new, a '99 Chevy Tahoe 4x4 with the 5.7L Vortec engine. The engine starts skipping and losing power pulling up a hill when exceeding 2,000 rpm. It acts as if it is starving for fuel, just like in the old days when the mechanical fuel pump went bad. The truck gets great gas mileage (22-23 mpg on a trip), and the problem does not exist when the engine is cold.
Here's a list of what has been replaced without correcting the problem: fuel pump, fuel filter (many times), fuel pressure regulator (five times), distributor cap and rotor (three times), spark plugs and wires (three times), fuel pressure line from filter to engine, catalytic converters, intake manifold gaskets, and the No. 1 fuel injector!
A little background information: When the truck was 2 years old, the engine started to skip and shake on a long uphill pull and the "check engine" light came on. Because the computer trouble code said the No. 1 cylinder was skipping, the dealer replaced the spark plugs, wires, distributor cap, and rotor. But the problem continued.
Later a dealer technician plugged a laptop into the diagnostic port under the dash and drove the vehicle. When the truck started to skip, he noticed the fuel pressure dropped off. So the fuel pressure regulator was replaced for the first time. It continued doing the same thing and the computer trouble code was showing that the No. 5 cylinder was skipping. Then the fuel pump was replaced, along with the fuel regulator for the second time. This did not get rid of the problem.