Originally Posted by oldskool66
it only leaks oil when there is load on the motor i can run it at 6k all day no leaks get on it on the free way and it blows oil at 2500... i replaced every gasket and seal including intake manifold timing cover valve cover gasket.
Apparently my simple answer isn't the problem, I hate that when it happens, then I've got to think.
When you say run the engine all day at 6000 and it doesn't leak with no load, expain how you're getting 6Krrrs and no load. I think I can guess but I'd rather hear your explanation.
If you're just revving the engine with no load on it there isn't a need for much throttle to get it up to 6000 RPM so the pressures in the cylinders are actually pretty low thus not a lot of forces to cause blowby. However, when the engine is truly working by moving a 2 ton car, the cylinder pressures get to be quite high even at a modest 2500 RPM this will make a lot of blowby.
If this is a blowby issue from a broken ring for example, as the cylinder pressures rise a lot of compression pressure will get into the crankcase and it will blow oil out the weakest place. Usually this comes out the breathers and often out the crankshaft seals or where the pan mates with the timing cover. Older heads with the cast gasket rail of the rocker cover are another common leak point as are the corners of the intake manifold. The pan rail can be another troublesome spot as often too much tightening of the pan bolts dimples the pan's stamped rail crushing the gasket, this can also happen to the rocker covers, and the timing cover if they are sheetmetal.
I'd think the locations of leakage would be visable; but if not, I'd clean the engine and take it out just enough to promote the leakage but short of soaking everything in oil so you can see where it comes from. I'd also recommend a leak down test in addition to a compression test. Low compression or fast leakdown can identify any ring problems. If the engine ever kissed serious detonation even for a few moments this can damage the ring lands grabbing the rings often busting them but not holing the piston. So the rings will fail to hold compression at some level from mild to wild but the piston won't have a hole right into the pan.
One might even consider the front of the crank got assembled without the oil slinger that fits between the crank's timing gear and the front seal. If the slinger isn't there; as crankcase pressure builds it will pump oil up the crank and past the seal like it wasn't even there. And yes wear on the seal surface of the damper can leak and leak a lot even though the seal itself is good. There are thin repair sleeves that slide down inside the damper to restore the sealing surface if this is a problem.