[sector95]

Is this a rebuilt motor? You say it only had 1500 miles on it. Did you rebuild it or was it aftermarket?

What kind of noise? The fan will make a lot of roar until the fan clutch warms up and allows a little slippage. And as "eti" eluded to, the noise might be coming from somewhere else other than the motor.

A *slight*, occasional engine knock is acceptable; the ignition control computer should sense the knock (thru the engine block knock sensor) and dial back the advance a bit.... the computer tries to give the engine as much advance (within the preprogrammed limits) as possible. An engine designed to run on 87 octane will have it's maximum advance set to operate effectively on this fuel.

The 4.3L is a 90 deg V-6 and as such is inheritantly unbalanced in it's firing. Early versions compensated by using an offset crankshaft and later engines had a balance shaft incorporated into the block. In either case, the engine sounds a bit "coarse" and that is normal. The non-balance shafted engines will tend to be a bit rougher in operation.

mike