1996 century wagon, just redid intake and all hoses, oil is clean, i use good mobile1 synth, no loss of coolant, motor runs decent enough to drive fine and get good gas mileage, however it sometimes feels as if it is stumbling just a little bit, but i NEVER get a misfire code. i am loosing a little oil, however i am not smoking at all, i see it on the front of the motor by front seal and under the rear side / rear of the pan or rear main seal. valve covers have new gaskets, and i did put the silicone in the little dip where head meets intake, no signs of leak there, also replaced the o ring on the dummy distro plug that operates the oil pump, no leak there either. it almost never drips, and when it does its half a dime size and its very rare although the underside of the motor is oily even after a complete washdown, no signs of oil leaking from top of motor, i even ran my finger under back valve cover gasket and under back head where i could and inspected with light where i could, given i could not get to every inch of it, but everywhere i got was dry as can be. two questions, what causes the engine to run a little rough, it doesnt matter if its idling or driving down the highway, and its off and on. (pushrods not mixed up, but rockers were just dumped in a bag during LIM replace, didnt feel it made a difference where they went) all vaccume lines hooked up right, no codes, all new sensors, i have not changed fuel regulator but it isnt leaking and injectors were all clean when pulled and i replaced the o rings, they seem to all pulse just fine. for all intensive purposes this cars runs ok, temp stays on 1/4 and if i sit still with no ac (neither fan runs when ac is off) it does rise but before it gets to half way the puller fan kicks on and cools it back down, if i let it get to that and immeadiatly cut the ac on the pusher fan comes on aswell to help out. but with complete tuneup, complete LIM and UIM job, throttle body clean, all engine running related sensors changed, all bad grommets replaced. pcv valve is original but not clogged, the stopper moves freely. i would think it would run like it rolled of the showroom floor. I did forget to hook the purge canister up for a couple of days then I smelled gas from it and immediately corrected the situation. why would i have a little front main leak and possible rear main leak thats a little worse than the front on a car kept in a garrage with only 100k miles on it, even the rubber on the windows and door seals is like new. this leak may not be front and rear seals but it is not the top end of the motor, i dont know where the oil pressure sending unit is but i havent looked for it yet, crank sensor was oily so i replaced it, i also replaced cam sensor since i had the LIM off. also these leaks dont seem to account for the amount of oil lost. once i noticed oil on the front part of the hood from left to right running back about half an inch, but upon inspection i could find no oil under the area to explain how it got there, i havent noticed it again i chalked it up to maybe i spilled oil when i changed the oil but i really dont think that was the case. say in a 1000 miles i loose about half a centimeter on the stick, i dont know how much oil this actually means is lost. and only the oil and tranny pan have oil on them, its not like the last car i had a rear main leak where it would leave traces on the driveway and it would drip off the back bumper and loose a quart in 100 miles. but oil is getting around on the underside of the motor so if its accounting for all my oil loss its dumping it out when driving and not idleing, i could let it idle for 30 minutes and it wont drip.
My suggestion about the oil leaks? DON'T use synthetic oil, especially if that kind of oil was not used in the car right from the start. Synthetic oil tends to be a little "slipperier" than the non-sythentics and will find its way out of the engine when regular oil wouldn't. I also would not put the word "only" in front 100,000 miles. That's plenty of miles for any engine to start developing some oil seepage here and there. It's just part and parcel of an aging engine. Whether or not the car is kept in a garage would have nothing to do with it. That'll affect the paint and trim, not whether or not the engine leaks oil.
Actually, the newest syn formulations take care of the 'slipperiness,' so it'll only leak as much as dino oil, but I sure do remember when it did 'slither' (my word choice) out the seals. But you are right about mileage; unless Ash Tray owned the car since new, there's not much of a way to see if it had an easy, medium or hard life. Only when they're abused or the wrong oil was used would you see it when the intake's off. So when you're not seeing puddles under the vehicle, look at the tailpipe. If you see black on the tailpipe, it's getting burned inside the engine. My Exploder's 5.0L is that way; it loses a quart every 1400 miles. BTW, there are markings on the dipstick; if you have the two drilled holes or the crosshatched area, that indicates full to 1 quart low. So keep an eye on the level, and when it gets to the bottom of the range, then look at the odom and see how many miles it took to lose one quart. One quart every 3000 is somewhat acceptable for a newer vehicle; I like no more than 1/2 quart every oil change (3-6K).
