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1991 Nissan Sentra Excessive Oil Burning
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BurninOil
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Feb 15, 2009, 9:32 AM
Post #1 of 17
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1991 Nissan Sentra Excessive Oil Burning
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Hi all. I recently have been having trouble with my old Sentra. Here are the details.
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.
This is the second crank seal I've put in it (original lasting 170k) and the first time the valve cover has been removed.
Any tips would be appreciated!
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Loren Champlain Sr
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Feb 15, 2009, 3:20 PM
Post #2 of 17
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Re: 1991 Nissan Sentra Excessive Oil Burning
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It sounds like you've got a broken piston ring or piston. When this happens, it over pressurizes the crankcase, which would explain your oil leaks. It will leak wherever is the least path of resistance. If you remove the oil fill cap with the engine running, you'll probably notice pressure, rather than PCV suction. Hopefully, I'm wrong, but doesn't sound good.
Loren
SW Washington
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BurninOil
Novice
Feb 15, 2009, 8:30 PM
Post #3 of 17
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Re: 1991 Nissan Sentra Excessive Oil Burning
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Thanks for the reply. That's what I was thinking as well. I forgot to mention but I also did a compression check and all 4 cylinders are between 180 and 182. I don't suspect it to be a ring since the compression is still normal. When the car is no stumbling and smoking (mid-range and higher), it runs perfect. Same performance as before.
(This post was edited by BurninOil on Feb 15, 2009, 8:33 PM)
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Tom Greenleaf
Ultimate Carjunky
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Feb 16, 2009, 3:33 AM
Post #4 of 17
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Re: 1991 Nissan Sentra Excessive Oil Burning
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Check your compression tester - that's unrealistic for a 227k engine that smokes like that - unless perhaps the cylinders are full of oil.
What do the plugs look like? Is PCV overcoming normal blowby?
Try pressure on cyl when at TDC and see where it blows out of,
T
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BurninOil
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Feb 16, 2009, 10:12 AM
Post #5 of 17
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Re: 1991 Nissan Sentra Excessive Oil Burning
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I used 3 different compression testers, all were the kind that thread into the spark plug (1 I own, 2 I rented), not the kind with the rubber tip you hold down. I've used the one I own on other vehicles that I know have bad rings and it shows a realistic number (70s for my old van on 2 of the cylinders). That vehicle pumps oil out the dipstick under load. I don't think it's the tool.
The plug tips are white/grey and clean, no oil. There is oil around the threads of the plugs up to the sealing washers but not a lot. The PCV valve has oil in it and so does both the vent lines off the valve cover. If it broken a ring, wouldn't it run badly all the time and make a lot of noise? The car idles smooth and starts right up. Running normally when it isn't puffing smoke. When it puffs, that's when it runs badly, but only for a few seconds and then it's back to normal. It's not smoking from every stop sign. Mainly if I drive highway speeds and then idle at a light. When I pull away, smoke. If it's a worn out ring, wouldn't it have been using oil prior to this? I've owned the car since new. Just seems odd it would break a ring coincidentally the only time I've pulled the valve cover off.
(This post was edited by BurninOil on Feb 16, 2009, 10:13 AM)
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Tom Greenleaf
Ultimate Carjunky
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Feb 16, 2009, 10:31 AM
Post #6 of 17
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Re: 1991 Nissan Sentra Excessive Oil Burning
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OK: It manages to "burn" enough oil to see it as said and consume it. Now I'm thinking of what connection taking a valve cover off would have and what I'm thinking is it isn't sealed well enough (guess) such that PCV system can't produce a slight vacuum to overcome normal blowby which is loaded with oil and the crankcase vapors are drawn back in thru the PCV which also should separate liquid oil from just the foggy vapor and isn't!
All kinds of things seal the crankcase and one is the valve cover. Off the top of my head - Oil fill cap, dipstick, front and rear seals, head gasket and perhaps intake gasket and certain hoses have check valved like the one to a common vac assist brake booster.
If pressure is allowed in crancase, oily vapor will invade, harm some hoses and blow out the weakest links first and likely make more weak links. Gotta make sure PCV system is doing its job.
Agreed - the compression test doesn't show a broken ring and seems like plugs aren't giving up any evidence.
Since this started with the valve cover change I'd go back and see if something isn't right with that. The area also must drain back to oil pan and if that fills with oil that can't return for some reason it can suck right down valve guides but you aren't seeing fouled plugs so I'm good and confused.
Never witnessed by me but I think problems with rings can happen such that they might test out fine and still be the issue??
T
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BurninOil
Novice
Feb 16, 2009, 10:35 AM
Post #7 of 17
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Re: 1991 Nissan Sentra Excessive Oil Burning
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Thanks Tom. I'll pull the cover off and see if I can find the oil returns and make sure the cover is sealing.
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Loren Champlain Sr
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Feb 16, 2009, 4:16 PM
Post #8 of 17
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Re: 1991 Nissan Sentra Excessive Oil Burning
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I agree with Tom on the compression test. However, if the cylinders are getting a lot of oil in them, the oil will really seal up that cylinder, but all of them? The odds are......can't find an infiniti symbol on my keyboard. How did the blow-by feel by hand? It's possible to lose a valve guide and suck oil, but all four cyls? Where's that symbol?
The cylinder head is pretty well open; Unless you've been using Pennzoil or Quaker State, I doubt that the oil return holes are so plugged that the oil would be forced by the valve guide seals. Gasket debris plugging the holes? Possible. Vacuum hose to the PCV connected to manifold vacuum? Sufficient vacuum? I've seen the passageways plugged. Hose from valve cover to PCV unrestricted, not kinked? So many questions. LOL.
Loren
SW Washington
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BurninOil
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Feb 17, 2009, 5:11 AM
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Re: 1991 Nissan Sentra Excessive Oil Burning
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Car has always had Quaker State. There is no residue or build up in the valve train area. No carbon deposits I can see. There isn't any gasket debris as the valve cover uses a large o-ring type of gasket and not a paper one. It fits in a groove on the cover itself. The PCV mounts directly on the cover so no vacuum leak in a hose to it. The hose leaving the PCV is a formed hose with a 90 bend (which I replaced due to it being solid feeling from years of heat). None of the hoses are kinked or restricted. When I turned the motor over while changing the front seal it felt like it had good compression.
Still scratching my head on this one. It's been this way for almost 2 months now.
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Tom Greenleaf
Ultimate Carjunky
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Feb 17, 2009, 6:00 AM
Post #10 of 17
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Re: 1991 Nissan Sentra Excessive Oil Burning
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Loren - you have to turn your keyboard sideways and hit the #8 key !!
There you go,
T
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Loren Champlain Sr
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Feb 17, 2009, 5:30 PM
Post #11 of 17
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Re: 1991 Nissan Sentra Excessive Oil Burning
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Oh, great! NOW you tell me!
Loren
SW Washington
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BurninOil
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Feb 18, 2009, 10:53 AM
Post #12 of 17
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Re: 1991 Nissan Sentra Excessive Oil Burning
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What about the metal plate that blocks the inside of the valve cover off? Is there something above this? Both of the 2 vents from the intake connect above this plate. One vent has the PCV in it. The hose from the PCV connects to the intake manifold itself. The second vent tube connects to the rubber boot from the airbox, with no valve, it's just an open hose. How is this hose not sucking oil all the time without a PCV in it? There must be something above that metal plate.
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Tom Greenleaf
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Feb 18, 2009, 11:29 AM
Post #13 of 17
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Re: 1991 Nissan Sentra Excessive Oil Burning
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Generally speaking the spot a PCV picks up vapor has baffles or a crooked path, or a steel wooly mesh to run thru in an attempt to separate oil droplets before PCV itself get a breath of the vapors to conserve on oil loss/burning. Some concepts are like the mesh over a stove that isn't or is vented for a grease collector in your kitchen type idea.
Perhaps in the recent work something was left out, broke, bent or something causing more oil droplets to get drawn in. Doesn't take many droplets to add up to real oil consumption - followed by clogging hose, ports, fouled plugs from excessive oil burning,
T
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BurninOil
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Feb 23, 2009, 11:06 AM
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Re: 1991 Nissan Sentra Excessive Oil Burning
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Nothing was left out during the work I did. Nothing broke, bent, pinched that I can find. The 2 hoses are very short, less than 6" and about impossible to hook up wrong. I may have to drill out the plate under the top of the cover to see if there is some kind of steel wool or other filtering device in there. I don't think I could have damaged it. I literally lifted off the cover, pulled the old o-ring (cover gasket) out of the groove it fits in, wiped off the sealing surface with a clean rag, put in the new o-ring and put the cover back on. The new o-ring isn't leaking. Since that first time I had the cover off, I pulled it off 3 or 4 more times looking for anything that might be causing this. So far nothing. Replaced the seals around the spark plug tunnels the 2nd time I removed the valve cover.
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Tom Greenleaf
Ultimate Carjunky
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Feb 23, 2009, 11:27 AM
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Re: 1991 Nissan Sentra Excessive Oil Burning
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To refresh this now long thread:
Oil "smoke" trouble began directly after replacing a crank seal AND the valve cover gasket on a 91 Nissan with some 227,000 miles.
Test show little so far as to why the sudden change but a problem was there to need those seals to begin with in a VERY high mile engine.
Oil burning and seen as smoke somehow isn't fouling plugs and evidence of severe blow by for any reason not conclusive to me at least.
Oil can be burned by excessive blow by, PCV issues or perhaps head gasket issues that were coincidental?? Oil separating at PCV shouldn't have changed with the work recently done. Not sure how that is accomplished in this exact engine. May not be a steel wool type deal but a series of baffles?? Simply dunno.
Rather than drilling thru cover for a view I might try clear hose temporarily to see what's going on thru the hose to PCV. Most clear hose wouldn't last so just a test.
It's not following a clear path of any commonly known issue that I'm familiar with so don't know what else to suggest. Perhaps a second set of eyes and hands on this would be a prudent choice?
Side note to be taken for face value: When an engine needs a rear main seal it usually means there is wear out of norms in crank bearings marking the beginning of the end of the useful life of an engine. Not encouraging but that's been my experience,
T
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BurninOil
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Feb 23, 2009, 2:33 PM
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Re: 1991 Nissan Sentra Excessive Oil Burning
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I appreciate the help and tips. It was the front main seal, which was also replaced at 170k miles. Second one lasted until 227k. I agree, I need to have some more eyes look at it and see. Obviously something is wrong that I'm just not seeing. PCV is oil saturated and so are both vent hoses which seem to indicate there is a pressure problem in the crankcase.
Thanks again for the tips!
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aartig
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Feb 25, 2009, 11:27 PM
Post #17 of 17
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Re: 1991 Nissan Sentra Excessive Oil Burning
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Yeah ...you are very true. I agree with you. Even I tried and found the same.
(link removed by moderator)
(This post was edited by way2old on Feb 26, 2009, 3:54 AM)
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