V6 Engine Rattle

[bond1]

The V6 engine in my 98 taco rattles, intermittently, hot or cold. The engine only has 50,000 miles on it, so this shouldn't be happening. It only rattles when the RPM's hit around 2000, while i'm driving. If I floor the gas the rattle gets louder, but it diminishes when the RPM's hit around 3000. Sounds like its coming from the back of the engine near the firewall. I tried changing the oil thinking low oil pressure. No change. I added marvel mystry oil to the engine oil, no change. I changed the high performance plugs out with standard plugs thinking detonation or pre-ignition. Rattle's still there. I took all the belts off the front thinking bad pully bearing. No dice. I added a can of fuel system cleaner to the gas, no change. I fueled up on high octane gas, and it sort of toned the rattle down, but not much. I checked the heat shields on the manifolds, they're tight, no cracks. The rattle sounds metallic, like valve clatter, its definately engine related. The previous owner had the truck supercharged, but put the stock manifold back on the engine when he sold it to me. I can't think of anything else to check. I'm going to try to disconnect the cat converter to see if that's where the noise is coming from. I can also make the rattle occur when i'm parked, but the rattle happens at about 3000 rpm. Any body else have this problem?

[bond1]

No luck, the catalytic converter is good. I replaced it with a straight pipe and the rattle is still there. Sounds like its coming from inside the cylinder head on the drivers side, near the back. Don't know. Maybe the engine's blown.

[TacoRuss]

Have you tried using a stethescope or even a screwdriver & ear to narrow down the noise??

Good Luck,

Russ

[ck_tacoma02]

Yes, same sound with my 3.4 V6 (now at 35,000 miles and started at 3,000 miles). The noise tends to occur under light loading such as when going up a slight grade or with moderate acceleration. I can’t hear it in 1st or 5th gears. It is loudest in 3rd gear at just under 3,000 rpms, although, noise will cycle on and off through the rest of the rpm band. Once the ears became sensitive to the sound I can always hear it but the loudness and intensity fluctuates randomly. I’m very good at picking up patterns but after two years of living with this ticking I am unable to determine the conditions that make a consistently loud sound. Exterior temperature has no influence, although, the noise is only present once engine has warmed up. Mileage of oil doesn’t seem to make a difference.

The sound when present (loudest) drives me crazy and the bloody truck sounds like a gigantic lawn mower. I have yet to find satisfaction with dealerships or Toyota.

I’ve met a few other people on the forums with the same problem but no one has either figured out or fessed-up to the origin of this noise. Valves that need adjustment is the most probable cause, however, my valves were checked and said to be within Toyota tolerances. This is still the best recommendation I can make, check the valves and adjust as needed. If they’re out of adjustment I bet that will fix it.

Keep us posted as to what you discover.

[bond1]

Good idea TacoRuss! I got my stethoscope and honed in on the noise. It was definately coming from the back of the engine. Sounded like the heat shield on the exhaust pipe that crosses behind the back of the engine. So I stuck a screw driver against the heat shield and the rattle changed to a dull rattle. Doh. I feel stupid. Guess I should have tried that first.