Heavy oil consumption mystery - My truck eats oil!

[JohnMasters]

Good morning fellow enthusiasts...

 

I feel that I have exhausted all efforts via research and repair and could use some guidance…

 

Heavy oil Consumption: 1 quart per 50 miles of spirited driving

1990 Pathfinder 4X4 SE VG30 5-speed, 135,000 miles

 

I purchase this vehicle off the side of the road in an area of town that I frequent.

 

The lady I purchased it from was very nice, mid 50s, with several cars in the yard and did not appear to drive the pathfinder very much. She purchased it in 1998 and had it registered in Alabama so it WAS NOT subject to annual emissions inspections.

 

I called and spoke with her mechanic who had worked on the Pathfinder in the past and who I happened to know as he is a trusted mechanic in the area whom I had previous positive dealings. He said the truck was not well maintained and that she DID NOT change her oil regularly but that the engine was in good shape and it just needed a better home.

 

The truck was filthy as if it just sat in the driveway and collected dirt for several years.

 

The odometer reads 135,000 miles which I fully believe as this truck is in great, low mileage condition.

 

After cleaning the truck and getting it ready to be my daily driver I noticed that it was consuming a large amount of oil but I could not tell whether it was leaking or burning as it didn’t smoke like a freight train as much as the large consumption would have suggested and there was NO oil leaking on the ground while parked.

 

There was some wet oil covering the underneath of the starter so I went about making a few repairs…

 

Replaced Plugs, Plug wires, Dist Cap and rotor button

Replaced the valve cover gaskets(they were leaking)

Installed a new Oil Pressure Switch(it was leaking)

Installed a new PCV valve(It was very gummed up)

Deleted the CAT(It appeared to be almost totally clogged)

Checked Compression(160psi+ on 5 cylinders, I haven’t done the hard one yet)

 

For the first several hundred miles I was using castrol high mileage 20/50 with one quart of Lucas oil stabilizer to slow the consumption but consumption stayed pretty consistent with very little white smoke.

 

At first the oil seemed to stay contaminated and blackish in color but after 2 oil changes in a few hundred miles it seems to be staying clean and clear now.

 

After the repairs I switched to Valvoline MaxLife 10/30 with NO stabilizer to see what would happen when the oil was thinner. the truck now smokes(WHITE) a bit more and it is easier to get it to pour white smoke out while sitting in neutral and revving the throttle up and down.

 

It appears to go through less oil when I baby the truck and keep the RPMs down.

 

I have looked at the possibility of valve stem seals being the problem but the VG30, based on research, doesnt seem to be plagued with that issue and I would think that the compression numbers would lead away from a ring related issue... or would it?

 

After the repairs, this truck runs great and has some good power too but is still eating oil so I am hopeful that I can discover the problem and use this as my daily driver. However I have been at it for two months and am running out of ideas but I hate to take it to the shop.

 

Any suggestions would be very appreciated!!!

 

John Masters

 

 

 

 

 

 

Edited June 8, 2015 by JohnMasters

[PathyAndTheJets]

Usually white smoke is burning coolant. Puffs of blue when you shift is usually valve seals.

 

Check your compression. You can do this quick and dirty by unplugging one plug wire at a time and listening to the rpm drop. The cylinder that reduces rpm the least has low compression and may be the culprit.

 

Just be careful, and try not to ground yourself to the body. It does not feel nice.

[JohnMasters]

Thanks for your reply...

 

Compression is at 160psi or better on 5 out of 6 cylinders. I havnt checked #6 yet.

 

The smoke would appear whitish/blueish.

 

I dont suspect coolant as their is no coolant loss, the coolant stays very clean and green, the truck runs cool and no symptoms have pointed in that direction. Although I could simply do a block test to rule that out. Which I will do.

Edited June 8, 2015 by JohnMasters

[adamzan]

Definitely not normal to use that much oil. I've seen vg30s with well over 250k use no oil. What about the lines that go to the pcv? Also have a look at where the trans meets the engine. If its wet the rear main could be leaking. But i would expect oil on the ground if it was that bad.

 

Check that number 6 cylinder. Sounds to me like you have a blockage in the crankcase vent system though.

 

Sent from my SGH-I747M using Tapatalk

[JohnMasters]

I also have a 1992 XE with 240,000 and it uses very little oil so I know what you mean.

 

I have checked and rechecked the PCV lines and hoses and they seem fine. There does not appear to be pressure in the crankcase as I feel no pressure coming from the oil cap hole or dipstick hole while the vehicle is running. I guess there would be a procedure for checking the PCV system with a mityvac(which I have) so I will look into that.

 

There is some wet oil towards the back of the engine but it doesnt appear to be the main seal. The Oil pressure sensor was definitely leaking a little bit so I assumed that was where that particular wet spot had come from and replaced the sensor.

 

A blockage in the vent would seem possible as apparently the previous owner was not regular at changing the oil and the truck just sat around.

 

My knowledge of exactly how the oiling system works and what each part such as the vent play IS NOT vast so I will do some homework on the vent possibly being clogged and gain some understanding.

 

I didnt check the compression on 6 because when I removed the tester from cylinder 5 the spark plug adapter stayed screwed into the engine and it took me like 10 minutes to get it out. If that were to happen on 6, Ill bet it would take more than 10 minutes. I would much rather have a compression tester that did not utilize an adapter. . Obviously I didnt have it screwed together tight enough.

[JohnMasters]

I was just doing some reading and saw this statement...

 

"A flickering oil light or a slight tapping sound in the rocker arm area on the topside of the motor is a good indication that not enough oil under pressure is reaching the top end of the engine."

 

There is, in fact, a slight tapping around the topside of the engine that does not exist on my '92 Pathfinder. This tapping seems to get fainter as the engine warms up.

[JohnMasters]

I talked to the mechanic a bit more about the persisting oil consumption issue and he is convinced that it IS NOT a Valve Stem Seal and that although the compression numbers are good, that one or more of the oil control rings are stuck or gummed up. SO...

 

Last night I did an internal engine steam cleaning by running the truck at 2500 rpm and introducing a few gallons of water into the upper intake via the brake booster line. Then, ran a half a bottle of seafoam through the intake as well. BE CAREFUL NOT TO ADD TOO MUCH WATER WHEN DOING THIS!!

 

I also replaced a quart of 10w/30 with a quart of Marvels Mystery Oil which is 5 weight, making the oil even thinner so that it may do some cleaning as it passes the rings.

 

I drove the truck for 15 or 20 miles like Tony Stewart and the oil level has remained unchanged so I will watch it for a few days and report back.

Edited June 10, 2015 by JohnMasters

[djeffrey]

Hmm never heard of using water. Interesting. Let's us know if your problem is fixed. Good luck!!

[JohnMasters]

Update...

 

The truck is running fine but still using oil at a steady rate.

 

I hate to do it but I have several projects that need my attention at this time so I will be selling this Pathfinder.

 

I decided to swap the rear drum brakes/axels from my current 92 XE with the rear disks from this 90 SE. It took most of the day but everything works great so purchasing this truck a few months ago wasnt a total waste of time.

 

Thank you for your input!!!