(non Porsche tech) Throwout bearings

[mjohnson]

What's the risk of driving a groaning throwout bearing until it breaks?

Vehicle in question is a 2002 Pathfinder, 94k miles

[mjohnson]

Question is meaningful as the thing is also burning a quart every 500 miles. I'd like to wait until I can find a replacement engine so as to save on the labor cost of a clutch/flywheel replacement.

[fastfredracing]

Really , the only risk I can think of will be a breakdown when the thing finally explodes. It will probably tear up the clutch diagphram which you will be replacing any way, and worst case scenario, it could tear up the throwout bearing guide tube on the front of the trans(unlikely).
Even when it catastrophically fails, there are pretty good odds you will be able to limp it home, may not be able to fully disengage the clutch though. Yep I would wait, and do it when you do the motor. Check car-part.com, should be pretty easy to find a motor for that

[Laneco]

I have a 91 pathfinder. To replace the throwout bearing (do the clutch) you are looking at around $800 just in labor as on my Pathy, you must remove the torsion bars to remove the transmission....

My throwout bearing is a little growly. I'll drive it until it fails and then drive it home in whatever gear I can get it into. I'll be into the repair for the same amount of money.

For a 94, I'd suggest you look into the cost of the clutch job as you might add that to the deciding factor. Maybe yours is cheaper than mine. I strongly suspect that when you add the cost of that in, you will replace the motor AND the clutch/TB at the same time instead of seperately...

As an aside, 94,000 miles and a quart every 500 sounds like a valve guide/seals may be amiss. 94K is pretty low miles for that oil consumption. Mine has 217,000 on it and I use a quart every 2,500 to 3,000 miles.

angela

[mjohnson]

Re: valve guides...

I'm preparing emotionally/$$$ for the whole thing, but I'd love it to just be the top end. What test would prove it to be the valve guides? I'm mechanically ignorant -- would a good leakdown test show any big oil consumption to be the guides?

Thanks,
mike

[john70t]

Leakdown and compression tests only show how well the chambers are sealing (rings, head gasket, valve seats).
The seal/guides are outside that.

You'll probably find obvious spark plug fouling in the cylinder coresponding to that guide, but the oil could be also be being drawn in by sticking or worn piston rings.

To find the bad cylinder, shine an infrared thermometer on each exhaust header- the cold one is not burning right.
Or, a balance test could find the suspect cylinder- Pull each plug wire until one does not cause a rpm drop.

Oil can also be drawn into the engine through the brake master cylinder(to all cylinders) or lost through front pulley seals, oil pan, or rear transmission seals. Look carefully on the outside first before concluding it's going into the engine.