Mechanics

EXCESSIVE OIL BURNING

1991 Nissan Sentra

Engine Mechanical problem
1991 Nissan Sentra 4 cyl Front Wheel Drive Manual 227000 miles

Recently the crank seal and valve cover gasket started leaking. I replaced both.

Next time I drive it, the car is smoking (blue) and stumbling when shifting. Just as you let off the clutch and accelerate. It also pings about half the time just as it belches out a large cloud of smoke.

I've replaced the PCV valve and found the 2 vent hoses coming off the valve cover soaked in oil. Prior to changing the valve cover gasket these hoses were dry.

The car burns 1 quart in about 150 miles. Highway speeds no smoke is visible. From a stop, up through the gears it smokes (cloud larger than the car).

Prior to the crank seal and valve cover gasket, the car burned NO oil. Not a drop in the 227k miles before this. The car also just passed CA smog with no problems less than 1 month ago.

Any ideas? I replaced the seals around each sparkplug tube and the PCV valve. I tried 2 valves, one aftermarket, one from Nissan. The 2 vent hoses from the valve cover were reinstalled properly.

On the inside top of the valve cover is a baffle that separates the PCV vent and breather tubes from the valve train. This baffle is sealed around 3 of the 4 edges and takes up about 2/3rds of the area inside the cover. At one end there is a slight edge where I assume it lets the area " breath" through the PCV and other vent hose to the intake. Is there something above this baffle that could have dislodged and is no longer keeping the intake from drawing oil off the valve train? The baffle is riveted in place so there is no easy way to remove it.

Still getting 36-40 mpg even with 1 quart per 150 miles of driving!

This is the second crank seal I've put in it (original lasting 170k) and the first time the valve cover has been removed.
Avatar
MiniDrivr
February 10, 2009.




No ideas?

Tiny
MiniDrivr
Feb 24, 2009.
Did you find out what is causing this? I have the exact same problem after a valve cover gasket replacement.

Tiny
Befland
Apr 1, 2009.
I still haven't found a solution. I also tried using compressed air to blow through the vent tubes to make sure there was air flow through that " plate" on the inside of the valve cover. It has air flow so I am completely confused.

It's using 1 quart every 115-150 miles (depending on how much freeway driving I do). It's running much worse as well due to the oil residue buildup. I've had to switch to premium gas to keep it from pinging.

Tiny
MiniDrivr
Apr 1, 2009.
If you take it to the dealer, let me know what you find out. I'll post an update if I ever solve this.

Tiny
MiniDrivr
Apr 1, 2009.
Will do. I've got to find out pretty quick because I can't drive it the way it smokes now. I'm almost sure it has to be something related to the PCV or hoses. Either the aftermarket valve was no good or I knocked something loose when I installed it. Maybe loosened something when I cleaned the underside of the valve cover?

Tiny
Befland
Apr 1, 2009.
I tried an aftermarket PCV and one from the local Nissan dealer. Neither one worked any better than the original one I was replacing.

Good luck!

Tiny
MiniDrivr
Apr 1, 2009.
OK.I replaced the PCV with another aftermarket one. I also replaced the hose from the PCV valve to the manifold (even though I believe it was ok). But before I put the hose back on I took a tiny screwdriver and scraped out inside the fitting that screws up into the intake. Then I took a shop paper towel (the industrial kind not the kitchen variety) and twisted it so I could get it up in the fitting. I also did the on the valve cover where the PCV screws into. After burning off the oil that was already in the system it has not smoked and it is running normal. I'll check again in a while when I go out at lunch but it seems to be fixed.

Tiny
Befland
Apr 2, 2009.
I had tried that on mine last month but it didn't help for very long (day or two). How many miles do you have on it?

Tiny
MiniDrivr
Apr 2, 2009.
Any update? Did that fix it for good for your car?
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Tiny
MiniDrivr
Apr 11, 2009.
Well it quit smoking but it's still using about 1 qt of oil every 100 to 150 miles. I cannot figure out where it's going. My steering rack is leaking fluid so it's hard to tell if there's oil leaking from somewhere too. It's not leaking around the perimeter of the valve cover and it doesn't seem to be burning it. I noticed when I took the valve cover off, there were some plastic pieces mounted to it. Didn't see where they mated to anything on the head. What purpose do these serve? Also.I assume that the cover goes in some kind of seal around the plugs. Wonder if I could have damaged one of those?

Tiny
Befland
Apr 15, 2009.

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