Oil loss w/o burning or leaking

subaru
outback

#1

over the last 6 months I’ve have to add at least a couple quarts of oil between oil changes but I can’t figure out where it’s going. it’s not burning oil (as far as I can tell) nor can I detect any leaks. I thought it might be a head gasket but I would have assumed I would see some oil residue around the crank case but it looks relatively clean. the car has 174K miles and is otherwise in good running condition. any ideas as to why I can to add so much oil? I’m also using high-mileage oil for each oil change. thanks for any help!


#2

At 174k, the engine could definitely be burning oil, but since your catalytic converter will remove most evidence of that from the exhaust, it will not be as apparent as it was back in the days before catalytic converters. If this is taking place, it will quickly put an end to that expensive catalytic converter, so you really do need to track down the source of your oil loss.

Another reason to quickly find the source of the oil loss is that you could have a breached head gasket or two. You failed to tell us the model year of your Outback, but, based on the odometer mileage, I am going to guess that it is probably in the 1997-2003 age range, and that is the group of Outback 2.5 liter engines that are very prone to head gasket failure.

If you are looking for evidence of a breached head gasket, instead of looking for oil residue around the outside of crankcase, you need to look for evidence of oil in the coolant overflow reservoir (a blackish line at the high mark for the coolant), and–even more importantly–evidence of coolant in the motor oil.

If you find evidence of coolant in the motor oil (it will look more or less like a chocolate milkshake), that is VERY bad news. Because coolant is not a lubricant, this type of dilution of the oil leads fairly quickly to excessive wear of the bearings, cylinder walls, and other friction surfaces. The result of excessive wear of the cylinder walls is–increased oil consumption–so, all of these scenarios could be linked. And, excessive wear of the main bearings will spell a quick death for the engine, so this is not something that you want to delay in investigating.

Check your coolant and your oil for cross-contamination, and then come back to this thread to report your findings.


#3

These days you can burn plenty of oil without really knowing it. At 174K you probably also at least have seepage from various places. Every little bit adds up.

However, if there was some change over the last 6 mos & you haven’t found any obvious leaks, check your PCV valve & feeder. Actually, check it anyway.


#4

Pretty good advice so far,

Also pull your plugs and look at them if they are very black or covered in oil there is some of your oil consumption.

You can also check cylinder pressure low pressure would indicate ring, head gasket or valve problems.

Also I would look back at the bell housing between the motor and trans, if the rear seal is leaking it might be running down and out there.

When you run the vehicle the pressure builds and you blow it out but when you turn it off the pressure drops and your leakage goes away cause it is not being blown out by engine pressure.

Good luck.


#5

Could you be a little more specific as to exactly how much oil it’s burning?? How many MILES per quart??