Knocking under load

[ToyLifer]

My '96 automatic DX has about 180K. Bought it last fall and it's been running perfectly. Previous owner had it serviced before delivering. I changed the oil/filter a couple of weeks ago--had a free coupon for new Valvoline NextGen oil, 10W40. Everything was fine for a couple of weeks, maybe 400 miles.
Then a slight knocking developed under load, only within a narrow RPM band--if the engine ran faster or slower, the noise disappeared. But this week, the band seems wider and the knock seems louder--doesn't disappear as fast, just knocks a little faster or slower.
Hard to tell where the knock is, but it seems mid-engine--I could be wrong. It's only when moving and under load. Oil looks good and is at proper level.
Valvoline hotline tells me I waited too long between changes (it was close to 10K) and that 10W40 is too thick for the engine, and that there's probably some sludge starving a valve or something. They recommend a flush and a fill with 5W-30 (I think they mean 10W-30. It's late spring).
Question 1: What's a safe and affordable flushing technique for this Tercel?
Question 2: If that doesn't take care of the problem (I am doubtful), what's the next step (assuming I'm short on cash)?
Thanks--
Paul

[Brian R.]

To flush the engine, before the oil change drain a quart of oil out and replace it with a quart of transmission fluid (ATF), and drive it without stressing it for a couple of hours, maybe longer. Drain the oil and change the filter. Add the 5W-30. 5W-30 is fine for your engine as they recommend.

Many people recommend Seafoam for flushing, but I don't believe in anything but tranny fluid. ATF is very close to motor oil in composition, but has a really high detergent content. More than one old mechanic recommended tranny fluid to me and I trust them explicitly. They know more about engines than I ever will.

I would seriously recommend against using solvent type flushes. Solvent flushes are only good for varnish, not sludge or other hard deposits. They can dissolve sticky deposits which hold other deposits in place. If the released deposits are not soluble in the solvent, they will be loose to cause trouble by blocking oil passages. This can kill your engine really fast. This is the advantage of using transmission fluid. It is designed to suspend deposits with a detergent additive which should break up particles before they can stick somewhere bad.

If this doesn't work, I would try AutoRX which is specifically designed to dissolve sludge. You use it as directed on the bottle. AutoRX is not a solvent, but is a type of oil which softens sludge and allows the oil to break it up. Read about it at the above link.

If nothing works, then I think you are either in the market for a rebuilt engine or a new car.

[cncvandy]

I had same noise in my 93 tercel, my neighbor described noise to a mechanic and he said it was the flex plate and sure enough, that's what it was!!! Flex plate was broke between big washers that hold it to crankshaft!!!!!!