Ready to give up!! Please help!

[luv2mud]

I'm at the end of my rope. Since last August I have replaced 2 motors and a transmission. Currently it is broke down AGAIN!!
My truck is a 2002 and had 257,000 miles on it when we replaced the first motor in August 2013. That switch was understandable. The truck had a lot of hard miles on it. I bought another motor with 104,000 miles on it. I figured with the miles I got out of the first motor this one would last me a while. That following winter while driving, it blew the rear main seal and I had to replace the transmission. After a couple of months I had to replace the lifters in that motor. In May the new motor started going. Burning oil, smoking and rattling so it sat until October when we decided to try another motor. After picking my truck up I started home and it blew the main seal and had to have it towed back. The seal was replaced and I finally got the truck home. We drove it around here a few times and the seal has blown again!!!
I have had multiple people working on this. My boys, a professional shop and a family friend that's a mechanic.
I am at a loss! Call me crazy but the thought of a new truck just makes me want to cry. I've had this one for almost 11 years and its just who I am.
Do I give up? Is there a reason its blowing the seals?


Sent from my HP 7

 

[Intender]

Clogged pvc system can blow a rear main seal. Too much oil pressure. Pressurise the crankcase and see what your getting before it opens the pvc valve. It should not take more than 5 or 10 psi to pop it open. Your probably getting too much oil pressure from somewhere

 

[drbandkgb]

this is sad

 

[robcarync]

Are you referring to the rear main as in the crank shaft seal in the engine? Or a transmission seal? Curious since you mentioned replacing transmission...wasn't sure if you replaced the transmission AND the rear crank seal, or if you blew a transmission seal...and thus replaced the transmission.

I am not an expert on the Xterra applications, but have seen this a few times on small engine equipment (commercial mowing, zero turns, golf mowers etc...same generic principle though...but there may be application specific things to check). If you have blown out multiple seals in the same engine, that would not surprise me. if you have blown out multiple seals from multiple engines, that would. Was there anything re-used from one engine to another? IE: breather systems/intake manifold?

When I have seen this on smaller engines (IE: crank seal literally blows out as if crank case is pressurized), it has been due to worn cylinders, allowing excessive blow by past the rings, and excessive pressure in the crank case that the crank case breather system can't vent efficiently enough. You can get an idea on the cylinder condition with compression test, leak down test, or crank case vacuum test.

It could also be due to abrasives in the oil, having worn down the bearing surface at the crank shaft where the seal won't fit tight enough. Not sure how the seal actually sits in this application, but I have seen on the small engines, the crank surface gets worn beyond tolerance to the point where the seals fall out. Replacing the seal won't help generally.

All of the blow by the rings should be vented back to the intake through the breather tube. There are usually some reed valves and oil separators, etc that the gasses go through before it gets to the intake side of the engine. If the breather valve or tube is clogged, the pressure will build until it is vented SOMEWHERE (IE: seals).

Again not sure on the Xterra specific set up, but these are some general areas I have seen on smaller engines...but should still be applicable. I wonder if the FSM has a test or spec for crank case vacuum?

 

[luv2mud]

All of this is above my head so I'm relaying the info to someone that understands....I hope! I appreciate the suggestions. Thank you!

 

[robcarync]

All of this is above my head so I'm relaying the info to someone that understands....I hope! I appreciate the suggestions. Thank you!

The easiest way to think about this is break it down to the basics: An engine is more or less sealed container. If a seal is being pushed out of the area it is supposed to be sealing, there are only 2 very basic options:

1) Either the pressure inside that container is TOO HIGH, which puts a higher than normal force on the seal, pushing it out.

2) The part of the engine that should be retaining the seal is not holding it TIGHT enough, allowing it to fall out when a normal sized pressure is pushing on it.

More Detailed Explanation:

If the engine is just worn out in the piston cylinders, the combustion chamber isn't sealed up enough. That means that each tiny explosion in the cylinder is losing power. Normally you want the power from the explosion to transfer the energy into movement of the pistons. If the seal is bad between the rings and cylinder, you will get a lot of gas/fuel mixture blowing past the rings and into the crank case. This will result in a higher pressure inside the crank case, since you have more fuel/air vapors being pushed into the crank case than usual. This corresponds to option 1 above.

Even on a brand new engine, you will have some of this fuel/air vapors blowing past the rings into the crank case. There is a breather system (PCV - Positive Crankcase Ventilation) that is basically a tube that connects the bottom end of the engine back to the intake side of the engine (tube may actually connect to valve cover...but there will internal passages connection crank case to that area). What should happen, is that the extra fuel/air vapors enter the sump of the engine, and the repeated cycling of the engine pushes the vapors back through the tube and into the intake side. Since the vapors are fuel and air that has not been burnt, it just enters the intake stream to get burnt on the next cycle. This is a great thing for EPA regulations and engine efficiency...older engines used to vent straight to the atmosphere. The breather tube will have some sort of check valves and drain back hole and maybe an oil separator. Ultimately, only the fuel/air vapors should enter the intake, and no liquid oil should make it that far. If there is a restriction (stuck breather valve, clogged tube, etc)...the pressure can't vent, causing it to build in the crank case. The pressure will build until the weakest link fails first. This corresponds to option 1 above.

Lastly, the seal mating surface can be worn. The smaller engines I have seen this on just have a press fit seal, so I am not sure how the Xterra seal is set up...it may not make sense in this application. If the engine is run for extended time without an oil change...or if dirt or other abrasives enter the oil, all of the oiled bearing surfaces will be scuffed up and have accelerated wear. If the area around the crank shaft is worn enough, there may not be enough friction to retain the seal. This would correspond to option 2 above.



What I would do: Check the factory service manual and see if they have the specification for a compression test, or a leak down test. This will give you an idea how good the ring/cylinders are sealing. If it looks good, check the factory service manual for a crank case vacuum spec, and measure the pressure of the bottom side of the engine. If it is high, then replace the breather tube and the breather valve.

Again, as disclaimer, I am not an Xterra expert, just sharing what I have seen and how I have diagnosed this issue on smaller engines.

 

[luv2mud]

Well...as crazy as it seems, i left my truck sitting for 2 months for nothing. Better to be safe then sorry but after hauling it to the shop and having a thorough inspection, there is nothing wrong with it!!
The mechanic said the only thing he can say is it was previously overfilled and it blew out the excess fluid. He cant see where there is any issues.
Soooo...the X still lives! Yay me!!

 

[Cruecible]

Woot!!

 

[drbandkgb]

Hell ueah

 

[robcarync]

Yayyyyy!!!!!!

 

[Amos]

The easiest way to think about this is break it down to the basics: An engine is more or less sealed container. If a seal is being pushed out of the area it is supposed to be sealing, there are only 2 very basic options:

1) Either the pressure inside that container is TOO HIGH, which puts a higher than normal force on the seal, pushing it out.

2) The part of the engine that should be retaining the seal is not holding it TIGHT enough, allowing it to fall out when a normal sized pressure is pushing on it.

More Detailed Explanation:

If the engine is just worn out in the piston cylinders, the combustion chamber isn't sealed up enough. That means that each tiny explosion in the cylinder is losing power. Normally you want the power from the explosion to transfer the energy into movement of the pistons. If the seal is bad between the rings and cylinder, you will get a lot of gas/fuel mixture blowing past the rings and into the crank case. This will result in a higher pressure inside the crank case, since you have more fuel/air vapors being pushed into the crank case than usual. This corresponds to option 1 above.

Even on a brand new engine, you will have some of this fuel/air vapors blowing past the rings into the crank case. There is a breather system (PCV - Positive Crankcase Ventilation) that is basically a tube that connects the bottom end of the engine back to the intake side of the engine (tube may actually connect to valve cover...but there will internal passages connection crank case to that area). What should happen, is that the extra fuel/air vapors enter the sump of the engine, and the repeated cycling of the engine pushes the vapors back through the tube and into the intake side. Since the vapors are fuel and air that has not been burnt, it just enters the intake stream to get burnt on the next cycle. This is a great thing for EPA regulations and engine efficiency...older engines used to vent straight to the atmosphere. The breather tube will have some sort of check valves and drain back hole and maybe an oil separator. Ultimately, only the fuel/air vapors should enter the intake, and no liquid oil should make it that far. If there is a restriction (stuck breather valve, clogged tube, etc)...the pressure can't vent, causing it to build in the crank case. The pressure will build until the weakest link fails first. This corresponds to option 1 above.

Lastly, the seal mating surface can be worn. The smaller engines I have seen this on just have a press fit seal, so I am not sure how the Xterra seal is set up...it may not make sense in this application. If the engine is run for extended time without an oil change...or if dirt or other abrasives enter the oil, all of the oiled bearing surfaces will be scuffed up and have accelerated wear. If the area around the crank shaft is worn enough, there may not be enough friction to retain the seal. This would correspond to option 2 above.



What I would do: Check the factory service manual and see if they have the specification for a compression test, or a leak down test. This will give you an idea how good the ring/cylinders are sealing. If it looks good, check the factory service manual for a crank case vacuum spec, and measure the pressure of the bottom side of the engine. If it is high, then replace the breather tube and the breather valve.

Again, as disclaimer, I am not an Xterra expert, just sharing what I have seen and how I have diagnosed this issue on smaller engines.

 

[Amos]

This is one of the best explanations of a PCV system I've ever read.