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My 89 745 Turbo is burning oil (Mobile 1) in a very strange way. This summer while climbing Fancy Gap, VA on I-77 on cruise the tranny downshifted into third - a bit later the engine went boom. Turned out the piston in #1 cyl. had melted,the oil was down two qts, and the radiator was nearly dry. Before this I was burning about a qt/2000 mi. So I get the engine rebuilt (including a new mitsubishi cartridge) and everything is great, no oil or coolant consumed in 1000+mi; I even made it up Fancy Gap again on cruise with no downshift or problems. The oil and coolant levels remained constant from N. Carolina to CT during a Thanksgiving trip. However upon returning down I-81 thru the mountains, I hit resume on an upgrade after slowing down for a semi and naturally the tranny down shifted into 3rd and held it for maybe two minutes at 4000 rpm (75mph set on cruise). Shortly after I stopped for gas, noticed a burning oil smell and found myself down over a quart, coolant was fine. Luckily I checked it, topped up, and had no engine damage. From that point on the oil level has not changed in 1500 miles around town. I feel certain that a load (uphill), higher rpm (4000), and boost (10-11 lbs w/Saab APC) cause me to loose oil in a hurry. This last (post rebuild) happened at night so I don't know about exhaust smoke. What is happening here? My crank breather assembly was replaced about 5K ago and cleaned during the rebuild so it should be functioning fine, all hoses have been checked - but what else can be causing this oil consumption if not this? Anyone have any ideas or similar experience? Oh yea first time I had oil leakage on the firewall from the dripstick tube, second time I could see no sign of leakage. Would a check valve on the line from the intake manifold to the "Y" fitting that closes under boost be of any use? I'm stumped.
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