Help - conflicting diagnosis - engine ruined by diesel

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se7en
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Help - conflicting diagnosis - engine ruined by diesel

Postby se7en » Mon Jul 10, 2017 10:41 am

4 years ago i filled up my tank with diesel - by mistake - drove it like that for about 25 miles - with lound explosins every 5 seconds and a lot of smoke.
Stealer cleaned it up. Cleaned it up again and replaced the cats.

Since then I add a gallon of oil to it every 500 miles.
In the first year every morning i would start the engine there would be lots of white smoke comeing out of the exaust. Nowadays I rarely ever see it.

All that oil is being eaten up by the engine somehow as there are no leaks. None.


Diagnosis 1 - a couple of mechanics have told me that the reason for oil loss is that the engine sucked in catalytic dust back into the engine which is what scraped the cylineds/pistons and this is how the oil is leaking into the engine.


Diagnosis 2 - just saw my mechanic who is very confident that this is not possible - he says the engine is running fine - he understands that it is eating way too much oil and that is a big problem. He could not tell me why the engine is eating the oil. Wants me to come in a few days later where he will take off the entire exaust and run it that way to diagnose. He thinks it is not the scraped cylinders/pistons.

Diagnosis 1 will end up costing $4000 - engine swap and 1 or 2 cats. Not a bad deal but a high number for me.

Diagnosis 2 has the potential to be under 2K. The probelm could be something else. What could that be? If diagnosis 2 is correct as my mechanic says and the pistons and cylinders are not leaking oil - how else could I be losing oil?
Re-boring the cylinders is an expensive undertaking.

Can anyone shed any light on this please?


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HiBRiD109
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Postby HiBRiD109 » Mon Jul 10, 2017 11:11 am

Wow this sounds like worst case scenario, usually an engine will shut off but you must had enough gasoline to keep the engine running. Burning 1 gallon of oil every 500 miles is insane. I had a truck that needed a quart of oil a day because the rear main seal was blown.

Judging by the fact that no oil is leaking out of the engine, that the oil is being burned. Do you have a lot of blue smoke or smelly exhaust? I want to say you have blown piston(s) and/or damaged cylinder wall(s) from the engine firing prematurely before the pistons could reach top dead center. The valves could also be damaged.

Either way, I think your engine is severely damaged and personally believe you should just replace the motor or replace the entire vehicle. You will be wasting money trying to diagnose the root cause because either way something in the engine is severely damaged. Your catalytic converters will also need replaced since i'm sure they are full of oil residue by now. If you were doing it your self, then I can see trying to fix the problem could be feasible but having someone else do it could result in a lot of money spent on labor and service.

Hows your MPG? Any knocking noise?

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se7en
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Postby se7en » Mon Jul 10, 2017 11:46 am

HiBIRD - thank you.

I think you are right. no loud noise other than loud engine when the oil is gone.
No blue smoke anymore. In the begining (1st year) especially winter mornings this was an issue - nowdays i see it only in winter mornings after i do my top off.
mpg is about 14.5.

going to see a mechanic now...

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Postby Kestral » Mon Jul 10, 2017 2:12 pm

I guess if the truck is in real good shape other then the motor and you like your truck I would replace the motor. First I would make sure the transmission is in good shape. There is a company I think it's called Jasper Engines you can look them up on line and they sell rebuilt Nissan VQ40 DE V6 motors I don't know what the cost but they come with a warranty. Do Not! Buy a rebuilt motor without a warranty. I would prob check with a few junkyards and see if they have any used low mileage V6 motors out of a Nissan Frontiers or Pathfinder's that were in a wreck?

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SETI20
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Postby SETI20 » Mon Jul 10, 2017 2:32 pm

That's insane usage. So many things can get destroyed when your engine is detonating like that with diesel in it. Most of the parts in there besides the crank and rods are aluminum.

I don't have a lot of experience with the Pathfinder engine, but I have a lot of "tuner" buddies that drive 350Z's and G35's and the VQ35 and VQ40 engines share a lot of the same parts. Most of them aluminum.
Broken ring lands and cracked heads are a common issue when things go wrong with bad tuning, bad mixtures and bad boost spikes. That causes similar absurd oil consumption. But usually you can tell where it's going. Filthy back bumpers, greasy exhausts, etc.

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Postby smj999smj » Mon Jul 10, 2017 4:38 pm

Just by what you are describing, it sounds like the engine is shot. But that said, why not do a compression test and cylinder leakdown test?

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se7en
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Postby se7en » Tue Jul 11, 2017 8:41 am

Thank you, guys!

Saw the mechanic yesterday, he drove it around, seems to think the engine sounds really good. He says it would be quite loud if the cylinders were scraped... 2 errors for engine light: P0153 and third cylinder misfiring.

Mechanic thinks we should fix these two issues. and go from there. Not sure this approach is best. Certianly makes me think this could be labor intensive - they were talking about valves gaskets... Going there soon - they will lift it up and look.

compression test and a leak down test is a good idea!

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se7en
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Postby se7en » Tue Jul 11, 2017 12:27 pm

Well I lied.
Got there - they asked me to step on the gas (i did for 5 seconds at 6500 rpm) - and there was smoke coming out everywhere. But there is no smoke when i drive in the city or just idling. They all agreed that the engine needs to be changed. Fiddling around with the pistons, gaskets valves etc. will be more expensive...
They said to run it till it dies and we will replace the engine.
In the meantime run it with diesel oil instead of 5W30. The guy there told me to use 15W40.

I really appreciate everyone's help!

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Postby eieio » Tue Jul 11, 2017 2:40 pm

smj999smj wrote:Just by what you are describing, it sounds like the engine is shot. But that said, why not do a compression test and cylinder leakdown test?
yeah!
doesn't anyone do compression & leakdown tests anymore?
it's probably the least invasive way to find out if an engine is toast or not
in addition, it gives an opportunity to check the condition of the spark plugs, the condition of which can have quite a story to tell as to the condition of the combustion chamber components of the engine internals
be sure to mark the plugs with the cylinder they came out of for future reference
.....there's an awful lot of guesswork going on out there, why not get the facts?

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smj999smj
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Postby smj999smj » Tue Jul 11, 2017 6:58 pm

se7en wrote:Thank you, guys!

Saw the mechanic yesterday, he drove it around, seems to think the engine sounds really good. He says it would be quite loud if the cylinders were scraped... 2 errors for engine light: P0153 and third cylinder misfiring.

Mechanic thinks we should fix these two issues. and go from there. Not sure this approach is best. Certianly makes me think this could be labor intensive - they were talking about valves gaskets... Going there soon - they will lift it up and look.

compression test and a leak down test is a good idea!
If the cylinder walls were scored by the catalyst media, it wouldn't make the engine sound louder. It would just create a poor sealing condition between the piston rings and cylinder bore walls, causing lower compression and an oil burning condition.

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Lord Farquaad
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Postby Lord Farquaad » Fri Jul 14, 2017 3:50 am

Maybe the fact that diesel does not ignite on spark, but on compression, made the ECU inject more of it to get/keep it going with the diesel in the tank. Maybe close to the point of hydraulic lock. This could have caused some rings to crack and break under these pressures that normal gasoline rings are not designed for?

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smj999smj
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Postby smj999smj » Sat Jul 15, 2017 4:51 am

Lord Farquaad wrote:Maybe the fact that diesel does not ignite on spark, but on compression, made the ECU inject more of it to get/keep it going with the diesel in the tank. Maybe close to the point of hydraulic lock. This could have caused some rings to crack and break under these pressures that normal gasoline rings are not designed for?
Diesel engines don't require an ignition spark in order to create combustion, but diesel fuel is still flammable and can very well be ignited by a spark...especially when run in a gasoline engine.

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se7en
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Postby se7en » Thu Nov 02, 2017 1:36 am

Since I am looking at a bill of 3500 to replace the whole engine.. do you guys think it would be a bit cheaper to just replace the piston rings and the valve seals? Those parts would be cheap I think. The labor cannot be more than 2k.

Is there a chance that this would not fix it?

4 years ago I drove the pathy with diesel in it for about 30 miles at 30mph was all I could do - very loud explosions every 5-10 seconds... now I go through a jug of oil every 3 weeks...


At the same time I'd put in new spark plugs and ignition could that I got for $120. And the two front cats - I'm hearing the rattle when acclelerating uphill with loss of power - and I'm pretty sure they are toast - they were changed when I put in diesel 4 years ago.

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Postby smj999smj » Thu Nov 02, 2017 9:21 am

You changed the converters a few years ago, but since then, the engine has been burning a lot of oil and contaminating those converters. So, upstream converters will definitely be on the list and at this point, I would question the integrity of the rear converters, as well. If you go back to an earlier post, you said a second mechanic said it's not possible for converters to come apart and score the cylinder walls. Twenty years ago, I would have agreed, but that's not the case anymore. Many vehicles today, like your Pathfinder, don't have conventional EGR valves; they use the variable valve timing to accomplish exhaust gas recirculation. They do this by cracking open the exhaust valves during the intake stroke to pull exhaust gas back through the exhaust valve and into the combustion chamber. If the catalyst substrate has deteriorated, bits of it can get sucked into the combustion chamber, as well, which will score the cylinder walls. To replace or rebuild the engine without replacing the upstream converters would be foolish, IMO. As far as the rear converters, I would replace them with Doug Thorley mid-pipes, which deletes the rear converters altogether (this may not be an option if you live in a state with strict emission testing).
The VQ is not an easy engine to rebuild. Replacing valves seals is a lot harder than it is on, for example, a small block Ford or Chevy, because of the overhead cams and use of bucket tappets. Some have had issues with head gaskets failing after a rebuild which I assume has to do with the inability to get the deck surface of the head within tolerable limits. May of today's engines (Ford's modular engines are a good example) need a mirror-like finish on the head to properly seal. Ford got to the point where they didn't recommend sending the heads out to a machine shop for resurfacing, rather simply replace the head with a new (and expensive) one. I have a feeling the VQ is similar in that the head surface needs to be basically perfect and free of any kind of imperfections, no matter how small.
The block is another story as we don't know the condition of the cylinder walls. If you are lucky, they well just need to be honed. Worst case scenario, they are damaged beyond the point of honing, they will need to be bored and new pistons will be required, adding a lot of cost to the job. Then, most techs will tell you to rebuild the engine and not replace the timing set is not a good idea, add-in more cost. You mind as well install a new water pump and thermostat while you are there and don't forget the cost of a gasket set, RTV, etc.
Personally, if it was mine, I would trade it in on another vehicle; maybe, get me a 2011 or 2012 Pathy. If the only option was to repair the vehicle, I would look for a 2011 or 2012 used engine for it. Note I specifically say 2011 or 2012, because those are the years that didn't have any timing chain issues and as a whole vehicle, it was also the years that all of the other "bugs" were finally taken care of. Then, with the used engine, I would get a set of Walker upstream converters, NTK upstream air/fuel ratio sensors and the DT mid-pipes. It would also be a good time to install headers, as the heat shield bolts on the factory manifolds are probably going to break, anyway. But that's "me." Obviously, you have to do what's best for you.

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se7en
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Postby se7en » Thu Nov 02, 2017 12:51 pm

SMJ - wow lots to think about. Not really - I just have to spend the $$$$. Thank you for your great help!

I think I will do exactly what you say:
new front cats, new sensor, rear pipes
And new spark plugs with new ignition coils that just arrived today.

Not sure what you mean by headers here: "It would also be a good time to install headers, as the heat shield bolts on the factory manifolds are probably going to break, anyway".

There is a place here in Vancouver Canada that specializes in engine replacements. Should I buy the engine myself or leave it to them? I will definitelly buy the cats pipes etc. Amazon seems to have good prices. What is a good site for engines this or is google my best bet?


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