2004 Subaru XT under powered and smoking after oil change

Question

Over the weekend I traveled home and back: about 140mi each way. About half way there the engine light came on, and, realizing it had been about 4500 miles since my last oil change, I added oil to the engine after arriving at my destination and confirming a low oil level. The car ran fine and the engine light did not turn on again until about half way back the other way. Unlike the first time, about 20 minutes after the engine light came on I noticed a lack of power at higher rpms and while driving uphill.

The next day I took it in to my mechanic to get a diagnosis. There were many, including a timing belt issue and an issue with the variable cam. He suggested starting with the cheapest solution first, and changed the oil and oil filter. When I got the car back I asked him if there was anything in the oil he drained: there wasn't, but he mentioned something about it smoking slightly from the exhaust. On the trip home I noticed smoke from the exhaust (it was not slight) and the same lack of power. I thought the smoke had a blue tint, but this morning it just looked grey. The mechanic told me to drive it for a week and come back if it continued to smoke.

There is no smoke from the engine compartment, and there was no smoke before the oil change. There are no dash lights on either. Also, the idle (and at all other rps) is smooth and it starts right up. Why would it have start smoking after an oil change and what would cause the lack of power? (not accompanied by smoke the first time around) Should I take it to a Subaru dealer, or to someone else?

Additional info: the car has 98500 miles, and the timing belt has not been changed.

Answer 1

Depending on the colour of the smoke that is produced from the exhaust it could be different sources, have you had a valve cover replacement done on the car? I've worked on some cars that have leaking valve covers where the spark plugs are located and this causes issues with oil seeping into the cylinders, which could be a source of smoke, and oil loss.

With the last Subaru that I worked on, we had to change the valve cover gasket, intake gasket, various evap hoses (heat cycle destroyed), and a water pump. I would suggest looking into doing the work all at one time, because doing the timing on the car takes a serious amount of effort to get to, and you might be able to save money on the labor.

I would start by looking for oil leaks, as well as trying to identify the source of the smoking, if you have a OBD2 reader, scan the car and see if anything is off.

best of luck! :D

Answer 2

I make no claim to be a Subaru expert but I have become aware of issues with the variable valve timing on GM vehicles. It seems some vehicles with this type of valve train are sensitive to oil viscosity. Oil that is too thick or to thin can result in poor performance. Is it possible that you added the wrong type of oil? If oil was induced into the exhaust system it could take several miles for the residue to burn off.

Answer 3

You say 2004 XT so I am guessing that this is a Forester XT with the 2.5 litre EJ25 engine with turbo.

The valve cover gaskets on EJ25's (and many other EJ engines) will leak oil if unchanged. The primary culprit is usually the spark plug well gaskets, which after a decade or so of heat cycling and compression go from flexible rubber to near rock. This is easy to see if it is ocurring as you simply remove the spark plug tubes and see if there is oil pooling around the gasket just inside the tube. More advanced cases will see oil making it's way down the outside of the valve cover. This can also impact the spark plugs as they may be sitting in oil which causes them to deteriorate over time.

The good news is that valve cover leaking is an easy job to fix. The bad news is that it may not be the issue as bad cases of this will result in oil on hot engine parts/exhaust and poor ignition (i.e. less power). It is unlikely that it would be causing smoke from the exhaust.

Smoke from the exhaust could be the result of one or two blown head gaskets. This can usually be identified by looking to see if there is oil on the driver's side (US) front half-axle - as the driver's side is usually the first head gasket to go. If there is oil there, it is most likely coming from the head gasket. An inspection under the car will allow this to be confirmed by looking at the line between the cylinder head and engine. Foresters of your age will range from a small seep to severe leaks. If there is a severe leak and the exhaust is smoking, coolant is probably being passed into the cylinder and thus the smoke.

If there is no head gasket problem (or only a small weep), then the issue may be timing belt related. The timing belts are very tough but according to a 2006 Impreza manual sitting in front of me, the timing belts should be replaced at 60,000 miles (or 100,000 km). So at 98,500 miles, you are nearly 40,000 miles past the replacement date. I'm uncertain what exactly will occur with a deteriorated timing belt, possibly smoke due but almost certainly poor power as the belt stretches and the timing goes off.

Replacing head gaskets and/or the timing belt are not simple jobs. You should try and ascertain the issue and find a Subaru non-dealer who will do these for you. The timing belt is critical as these are interference engines. If the belt breaks, you will be looking for new valves, new cylinder heads and thus likely a new engine.