YoSammyT

I just finished a rebuild on a 1990 sbc 350. I probably don't even have 100 miles on it. The engine is out of a 1990 C1500, but it's now in a Datsun 280Z, mated to a turbo 350 tranny.

I have a difficult to find oil leak. No leak at idle, but after driving it it will leave a puddle under it, and it smokes from oil slinging on the header when driving. So, I put the car up on stands and let it sit and run for around 15 minutes. Again, there is no leak at idle when hot or cold. No noticeable leak at 1,500 rpm either. However, if I rev past that it drips very noticeably from the bottom of the rear main seal housing. Some of the drops hit the outside edge of the fly wheel which slings oil on the header and up in the transmission housing.

If I rev the car up a few times to 4,000 rpm or so and then quickly get under it, I can actually see it leak several (7 plus) drops of oil, then it stops leaking.

I had two breathers with no PCV, but they pretty quickly became saturated with oil, so I utilized a K&N part that vents the valve cover directly to the side of the air cleaner and I'm not using a PCV valve, just a straight vent to the air cleaner on both sides.

It's my understanding that a one-piece rear main seal... 1. typically doesn't leak 2. when they do leak, they'll leak at idle as well as any other rpm. Am I wrong? I've never had this happen and I'm at a loss here and could use some advice. I really, really don't want to have to pull the engine back out.

Thanks for the help.

ATX-Iroc

Did you forget the dipstick tube? Done it before😔

v8sten

iTrader: (5)

if its slinging it from the flexplate then its the rear main seal

ironmanLS1

iTrader: (9)

Back of intake, oil pressure sender, valve cover, oil pan. Just a few of the places. I would do a thorough cleaning and then start over looking. Don't forget to check your oil level so you don't run low on oil.

1 FMF

iTrader: (1)

i would get a vacuum gauge and measure crankcase pressure under the operating conditions you are having the oil leak. it sounds like a crankcase pressure problem which is often the result of a poor pcv setup... and you don't necessarily require a pcv valve. you don't want crankcase pressure over 1 psi, if it's over 2 psi it's definitely a problem or will be. ideally you want a slight vacuum or crankcase pressure not more than 1 psi lower than atmospheric. too much vacuum on the crankcase is bad because then atmosphere will be pushing in on your front and rear crank seals and then cause them to leak.