Oil leak on '94 Mitsubishi Mirage - what's the source?


#1

Our '94 Mirage ES, affectionately known as “The Dentmobile” for its uncanny ability to attract other vehicles to bump into it in parking lots, is now in the hands of the fourth driver in the family. It’s been reliable commuter car, student car, etc.



I recently introduced my teenage son to the joys of bondo and fiberglass by lovingly fiberglassing the rusty roof, pounding out and bondoing the dents, smoothing and wet sanding the finish, setting up the compressor and set of paint stray tools…and then the reliable engine decides to have a nervous breakdown with bout 86,000 miles, literally dropping all the oil on the driveway.



Symptoms that led up to this? Recently, my teenage son complained that the oil light was coming on. Since he’s not a motorhead, the concept of running a car without oil didn’t create a sense of urgency.



I gave him the SAT comparison about oil is to cars as blood is to humans.



So we looked for leaks, topped the oil, ran it for a few minutes until warm and no drips, runs or errors. I waved him to night class and had him stay close to home where speed limit is 25 and he could walk home in an hour should the car die.



Next morning, oil is all over the driveway under the car. I checked the dip stick, and 3 quarts are gone…again. I know the kid isn’t selling used 10w40 to his classmates.



Filter was tight. Oil pan plug is tight. Some oil pan bolts were 1/4 turn loose. No oil around head gasket or plugs. No oil around valve covers.



But…under the engine, way at the back (past cylinder 4) of the engine where it bolts to transmission (aka when facing car the left most side of engine under the hood) there is oil dripping a few drops a second. I think it could be coming from the area where the drive shafts exit, but hard to tell due to the dirt, the viscosity of the drops sticking to metal until a low point, etc.



Other observation - he’s been complaining of reduced mileage before the oil problem became pronounced. We used to get 30mpg, he’s getting 20 and isn’t a lead foot. Car does not burn oil, rings are fine, no blue smoke, no black or white smoke, recently passed smog test.



Is it possible the rear main engine bearing is shot and causing leaks? Is there some plug near oil pan level or other bolt that could be loose? Is there some part on this area of engine/automatic tranny that vibrated off? I saw all the freeze plugs in place and no leaks from them. Oil pump looks happy, as do the water pump and front of engine accessories.



Do the drive shaft bearings or silent shaft bearings wear out and weep oil under stress of in motion? Is it possible the tranny and engine bolts are loose? I don’t hear strange sounds when driving, coasting or sitting.



Is The Dentmobile ready for the big parts-shop in the sky?


#2

If your noticing a sizable leak where the engine mates with the transmission, it is indeed the rear main seal blown. And, you will need to drop the transmission and remove the flywheel to get to it. This leak sounds too large for any Stop-leak additive to work.

As for the reduced mileage, pull out and check the spark plugs. If the tips are oily or black, then this may be the reason the seal blew out, excessive blow-by from bad piston rings. You’re burning oil, it’s the catalytic converter preventing the smoke from coming out. To get an accurate picture, find a good independent mechanic, and have a leak-down test done. This test will check the condition of the combustion chamber and cylinder seals, ie valve seats and piston rings. If this tests OK, it may be worth the expense of fixing the rear main. If the test is questionable, then you may want to figure on rebuilding the engine instead, or looking for the next “Dentmobile”.


#3

The repairswill definitely cost more than the car is worth. Changing the rear seal will help for only a little while if the main bearings aren’t changed. The car is definitely ready to go its own way. If you can’t find an open hose or connection to the crankcase, you may have an expensive fix.


#4

Great advice!

I suspect there’s a new Dentmobile in our near future, it doesn’t make sense to rebuild an engine on a cheap car.