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Sedans Nissan Altima Nissan Altima Engine Failures
500 messages, Last post on Nov 29, 2009 at 8:42 PM
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Replying to: electricdesign (Feb 28, 2008 9:23 pm) I suspected the head gasket at the onset of the oil consumption problem. But I instructed the mechanic to ensure this was the problem before spending the money to replace it. He did the carbon test on the coolant and found zero trace and concluded there was not a head gasket problem. I have added water to the resevoir a couple times in the past weeks, which still points to a head gasket. I will observe for bubbles as you suggets and let you know. The engine has never overheated, at least not yet. Like you, my mechanic also thought it was a good thing that all four cylinders had compression that was +/- 2 PSI of each other. I'm guessing he used a plug gauge, not a threaded guage, which may explain why the readings are lower than expected. I'll confirm his method and let you know. My mechanic also mentioned the importance of valve guide seals. If you remember, he would like to open the valve cover to see if I have a plugged oil return port that is causing the oil to accumulate in the top side and leak out the PCV valve (by the way, what do you think of this theory?). He also indicated that the valve guide seals have an umbrella shape, designed to shed oil coming from the top side, and if the oil was accumulating, the oil would rise under the guide seal and possibly escape. This sounds different than your description of the seals, which you indicate is submerged in oil. Can you say if his theory has merit? I've used him for years and he's very reputable, but perhaps he's not seen this engine torn down like you have. One thing I forgot to mention in the previous post, the engine oil is black, real black. It gets black very quickly, even after a complete change. And it stays black, even though I'm replenishing it with a fresh quart every 200 miles. How difficult is it to get the precat and exhaust manifold unbolted from the head? In the past, I've had bad luck with head bolts - they are usually pretty stuck and I'm afraid of twisting one off. I'd like to disassemble the precat and inspect it for integrity and see if any material inside is loose. And will the 2nd cat disassemble pretty easily? If either cat is shot, I'll have to replace because PA tests annually for emissions. But I don't want to replace the cat if I've already damaged the cylinder walls badly. I guess I could clean the debris out of the cats and run them "empty" for a while to see if that solves my oil consumption problem before replacing with new cats. I'm a weekend mechanic, more of a do-it-yourselfer, and not sure I should attempt to take the cats apart at home. And finally, please help me understand how a bad cat causes cylinder wear and oil consumption. Does a clogged cat cause the exhaust and cat chemicals to back-up into the engine? Does that corrode or wear the cylinder walls? Since I'm now using 1 quart / 200 miles, does that sound to you like it's too late to save it? And if I'm burning 1 quart / 200 miles, whether it's from scored cylinders, bad head gasket, or leaky valve guide seals, why don't I have a sooty black carbon buildup at the tail pipe? Thanks for taking the time to read. Hope your weather is better in FL than here in NW PA.
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Replying to: boating (Feb 29, 2008 8:02 am) 1, not every altima, actually a pretty small amount, suffer from the oil consumption problem. 2. It is almost exclusive to the 2002 model year 3. The QR25DE engine was first used in 2002. There were, like with anything else new, some issues with it. those issues have been taken care of. 4. then engine itself is solid. its the cat, actually the precat, that was causing the problems. If your not really interested in the altima, or are just looking for a reason not to buy one, then don't get one. you'll just worry about it all the time. But, If you really like the car, and are really interested in one; I wouldn't let the problems with the first year of the 2002-2006 (3rd generation) redesign featuring a brand new never before used engine keep you from getting one. |
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Replying to: scttcrssmn (Feb 29, 2008 10:48 am) I'm really busy tonight, so I'll answer the rest of your questions tomorrow. Many of the questions that you ask are answered in my previous posts from #75 until now. I'll address just one issue right now, the valve seals, and this could apply to most engines, but especially to this one. Your mechanic is saying the same thing I said, it's just your interpretation that is different. Yes the valve seals are unbrella shaped, I knew that, and 99.9% of them are, because they fit over and cover the end of the valve guide like an umbrella, this is a very normal and usual fit. But imagine if an umbrella gets submersed in water, it wont do you any good, you'll still get wet! In other words, if you are under water, an umbrella won't do you any good, unless it's seal tight around you. And as I said before, the valves, guides, springs & seals are located in pockets in the head, so the valve seal runs largely under oil, and does shed oil that falls from above it, but most of the oil is running down the sides of the pocket down to the valve guide. This valve guide depends more on the seal itself fitting tightly onto the stem. As the valve seal gets old from age and hardens from the heat, the valve stem slips up and down on the seal and the seal between the valve and valve seal becomes less of a good seal, it gets loose. Once oil can leak between the valve and the valve seal, it can reach the valve guide where vaccum around the intake valve can suck some oil through the valve guide and into the combustion chamber on the intake stroke. It takes a special tool to remove the valve springs from the head, that why it needs to be done by a professional machine shop. The bottom line is you may need valve seals, and the best way to do that is to pll the head off and get it professionally rebuilt like I had mine done, then there is no more problem. I suppose that you looked at all the pictures of the teardown and rebuild of the engine that I linked in previous posts. You can also download those pictures, they will be very helpful if you need to tear down your engine. But before tearing down anything, we need to do all the diagnostics first. I'll answer more later. Yes, be sure the oil drain pockets in the head are clear and open. More to come soon. E.D. in Sunny Florida
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Replying to: electricdesign (Feb 29, 2008 5:00 pm) A little more info for you today. I warmed the engine up today (25 degrees here) to make sure thermostat was open, then opened the water reservoir to watch for bubbling. Had to add water first because it was empty again, indicating either a leak or head gasket, correct? Had the engine running constant at 3,000 RPM, but no sign of bubbles, at least not for the 15 minutes I observed. Had the oil changed three days ago, so I checked the dipstick today to see its condition. It showed full, but I've only put a few miles on it. However, the oil is black again, so it's being exposed to combustion somewhere. This is the reason my mechanic thinks the oil drain pockets may be plugged. What else do you think could be causing fresh oil to blacken almost immediately after a change? Sure wish I could figure this out. Don't mind spending the money to replace head gasket and valve seals; just don't want to put it back together only to find out the oil consumption is still bad. One more item of interest. While I was observing the reservoir for bubbling at 3,000 RPM, after about five minutes, the engine suddenly went to idle RPM but did not idle smoothly. Instead it would run at idle, then run up to 1,300 RPM, then idle again. I thought maybe my prop on the accelerator pedal slipped, but it was firmly in place. I reset the prop, watched for bubbles, five minutes later, the engine did a repeat performance of dropping down to idle. Any idea why it cut out like this? Thanks for spending the time with this. I appreciate your insights.
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Replying to: scttcrssmn (Mar 01, 2008 12:06 pm) 1. "Mileage got into mid 90’s in late 2007, car started to run rough occasionally, like when there’s condensation in the fuel. Problem was intermittent. Used isopropyl in fuel, but that didn’t fix it. Also, the heater started blowing cool when idle, which made me think low water or weak water pump. Took to my Goodyear mechanic, a good guy and capable mechanic. Looked at computer codes, suggested changing gas cap to clear the codes and radiator cap to see if that improved the heat . He also backflushed the heater core and it got better for a few thousand miles, but it still continued to run rough occasionally for short bursts of time." The occasional rough running, heater running cool, and loss of coolant all point to a head gasket leak. You must check out the cooling system as I outlined in my post #214, point #1. "I warmed the engine up today (25 degrees here) to make sure thermostat was open, then opened the water reservoir to watch for bubbling. Had to add water first because it was empty again, indicating either a leak or head gasket, correct? Had the engine running constant at 3,000 RPM, but no sign of bubbles, at least not for the 15 minutes I observed." You said that right, having to add water to the coolant reservoir is a sure sign of a leak, and if it is not and external leak, then it is likelly a head gasket leak. I found the bubbles with the engine idling, that is the way you should check it. If it is real cold, the fans probalby wont come on anyway, if they do that means the engine reached full temperature, usually about 200 to 202 degrees, then the fans cut off when the temp drops down to about 188 degrees. 2. "Then the excess oil consumption started. Maybe 1 quart / 1,000 at first. Took back to Goodyear January, 2008. Replaced PCV valve, but no change in consumption. Back to Goodyear again February, checked water for trace carbon, but zero. Checked oil for presence of water but none. Compression check yielded 149, 151, 150, 149 which he thought was OK (do you agree?). Did leak down test and pressure held good. Pulled the plugs but they were dry, with a little white powder residue. Replaced plugs. Mechanic found oil in line leading from PCV valve so he replaced the valve again in the unlikely event that the new one he installed the first time was bad. Car is now using about 1 quart / 200 miles. Mechanic thinks he should remove valve cover to see if oil return ports are clogged, allowing oil to accumulate in top side of engine, filling to the point where the PCV is located and allowing oil to escape there." Compression low but even, may be ok. Yes, check oil return holes in the head. 3. "So, my question to you – is there any merit in pulling the valve cover and checking the oil return ports, or is it a foregone conclusion that I have the dreaded catalytic converter problem?" Yes, check oil return holes in the head. And you MUST check the exhaust and Cats as I outlined in my post #214, point #2. 4. "How difficult is it to get the precat and exhaust manifold unbolted from the head? In the past, I've had bad luck with head bolts - they are usually pretty stuck and I'm afraid of twisting one off. I'd like to disassemble the precat and inspect it for integrity and see if any material inside is loose. And will the 2nd cat disassemble pretty easily?" The Precat comes off fairly easily, you need to squirt WD40 on all the bolts and threads that you will need to loosen, to help them come off, the heat shield may be the hardest thing to get off, the little bolts can be tight to get off. Once that is off, use a special oxygen sensor socket to remove both the oxygen sensors, then underneath the car, disconnect the exhaust pipe from the Precat/Exhaust manifold, remove the studs, as it makes removing the exhaust pipe easier. One of the studs was stuck tight and I had to use a torch to heat the area of the manifold near the stud red hot before I could get the stud loose. Once that pipe is loose at the front end, you can unbolt the back end of the exhaust pipe at the bolted flange in front of the muffler (it has 2 bolts with 2 nuts, very tight, use lots of WD40). Remove this pipe, it has the 2nd Cat in this pipe. If this cat is plugged or restricted, you can unplug it at this time, using a metal bar or rod and a large hammer you can knock the stuff loose out of the end of it to clear the pipe. Now back to the Precat/Exhaust manifold, Loosen and remove the bolts and a small metal support bracket at the bottom of the assembly, it connects the precat to the engine case to give the manifold some lower support. Once all that is taken loose the only thing that should be holding the manifold are the nut and studs bolting it to the head. Soak them with WD40 and the nuts should come off with no problem. The Exhaust manifold gasket is a very nice metal gasket that can be reused it you don't damage it. Once the nuts are removed, put the manifold off the studs and lift it out and check it out completely. If it is damaged or plugged, you can unplug it at this time. Putting it back on with the cat unplugged will cause the service engine soon light to come on with the code that says catalyst efficiency below threshold or simply "bad cat". 5. "One thing I forgot to mention in the previous post, the engine oil is black, real black. It gets black very quickly, even after a complete change. And it stays black, even though I'm replenishing it with a fresh quart every 200 miles. " "Had the oil changed three days ago, so I checked the dipstick today to see its condition. It showed full, but I've only put a few miles on it. However, the oil is black again, so it's being exposed to combustion somewhere. This is the reason my mechanic thinks the oil drain pockets may be plugged. What else do you think could be causing fresh oil to blacken almost immediately after a change?" This is not a good sign, it could mean that the cylinder walls are damaged and that the rings are not sealing. The only good way to tell is buy pulling the head and actually inspecting the cylinders, checking the finish of the clyinder walls and measuring them with an inside micrometer. In the case of my daughters 2002 Altima 2.5S, I was lucky, as the cylinders looked in good shape and they were not worn. The oil consumption in my case was fixed with the new valve seals, and the head gasket leak was fixed with a head rebuild, milling the head flat and new gaskets. 6. Continued in the next messege.
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Replying to: electricdesign (Mar 01, 2008 3:37 pm) 6. "And finally, please help me understand how a bad cat causes cylinder wear and oil consumption. Does a clogged cat cause the exhaust and cat chemicals to back-up into the engine? Does that corrode or wear the cylinder walls? Since I'm now using 1 quart / 200 miles, does that sound to you like it's too late to save it? And if I'm burning 1 quart / 200 miles, whether it's from scored cylinders, bad head gasket, or leaky valve guide seals, why don't I have a sooty black carbon buildup at the tail pipe?" The chemical ceramic material (like sand) comes out of the cat and into the exhaust ports and into the cylinders and eats up the cylinder walls and piston rings, allowing oil to leak up past the piston rings into the combustion chamber and burn up with the gasoline. The oil burns clean, so you don't get much soot, I'm not sure why it burns so clean, maybe computer controls helps it to burn more completely by advancing timing and adjusting the air/fuel ratio. 7. Finally, give me what ever information that you can, but it appears to me at this time, if you want to keep driving this car, you will need to set aside a pile of money and set some time aside out of your schedule and put your car on the calendar to do some major work on it. After everything else externally is checked out, you will need to tear down the engine and remove the head for an "Exploratory Teardown", send the head out to be resurfaced and rebuilt (New valve seals and check for cracks or leaks), And check the cylinders very carefully, lightly file the top of the engine block with a long straight file to be sure the deck is flat. If cylinders are good, you may put the whole thing back together like I did, but if cylinders are bad, the engine has to come out. Then you can decide to either rebuild that engine, or replace it with a rebuilt engine. Good Luck, E.D. in Sunny Florida
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Replying to: electricdesign (Mar 01, 2008 3:44 pm) Thanks for the detailed reply. I have been off line for a couple days. I will read thoroughly and get back to you. |
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Hello all, I wanted to let everyone in on what is going on with my very own 2002 2.5 altima with 85,000 miles. About 3 weeks ago I was driving home from work and the OIL light came on. I thought it was just from driving the car from Indiana to Florida and putting so many miles on it in a short time that may have burnt off some oil. I checked it and there was no oil on the dipstick. This freaked me out a little bit and I took it to get the oil changed. About 10 or so days later the OIL light and also the SES light came on. I checked the oil again and there was once again no oil on the dipstick. I put more in it myself and checked to make sure the level was correct after running it for a bit and the oil was BLACK. Very strange after putting brand new oil in. My dad looked around the Internet and found the forums on this problem. I took my car to NISSAN to get it diagnosed and they said the oil was mettalic and that showed signs of wearing on the cylinders. Now that it was diagnosed I called Nissan and after around a week or two ago got an answer back saying they couldn't do anything about it since it was out of warranty, which is understandable but something doesn't seem right about the whole ordeal. Now I am stuck in a perdicament to either rebuild, replace or trade. Any suggestions?
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Replying to: seanakio (Mar 05, 2008 7:43 am) |
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Replying to: seanakio (Mar 05, 2008 7:43 am) Thanks for sharing your experience and I hope it works out for the best for you.
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