3rz rumbling noise.

My '96 3rz with 260k+ miles has been making a rumbling noise for a while now. Sounds like it's coming from the motor, but I don't hear well enough to trace exactly where.

It's a rumbling that sounds sorta like a throaty exhaust or maybe an old carbureted motor burbling. It varies with rpms and gets the most loud under max load - like when the motor maxes out and won't give me any more juice while climbing up a hill or trying to accelerate. It maxes out a lot these days - really low on power.

I've done a compression test, and the numbers came back pretty low. The middle two cylinders are 130s, and the outside two are 150s.

I'm pretty sure it's not an exhaust leak - I've replaced all gaskets and tightened all connections, and I have the mini header and not a cast manifold. It's not transmission related - I've put a rebuilt one in and double checked everything - plus the noise is there at idle in neutral.

Will a bad valve (or valves) make this sort of noise?

What else could sound like this? A bearing in the motor?

How do I tell which it is?

Motor uses virtually no oil. Just drove a 6800 mile road trip from NC to Idaho and back with about 1000 lbs loaded on it, and it only used maybe 1/2 quart through all of that.

If the bottom end is good, I will throw a new head on and keep driving it. If something is bad in the bottom end, though, I don't want to spend the time and money on a new head.

 

bump.

 

Bump for solution.

 

260 k is getting long in tooth even for Toyota have you considered a lower mileage salvage engine?

 

Just a some WAGs, here, but it could be the chain tensioner, if that is still original ...
or maybe the distributer bearing (do a 'stethoscope' test).

 

Yeah, I've considered it. But if my bottom end is still good, I would much rather spend the same for a brand new head than roll the dice on a used motor. Every used motor is a crapshoot unless you know the person who owned the donor truck.