First, I don't know the exact year of this I-6 (see https://www.ford-trucks.com/forums/s...d.php?t=292878 if you can help me identify the year) but a fair guess is mid- to late-80s.

The engine runs nice and quiet when cold and as it is warming up (there is some very light tapping from the valve train, which I understand is to be expected). As it approaches operating temperature I get much louder tapping noises from the top of the engine. Take a screwdriver and rap as fast as you can on the valve cover -- that's what it sound like. And sometimes there's a double tapping -- like you're doing it which two screwdrivers, one in each hand.

Periodically the noise goes from single-tapping to dual-tapping and back. And then it will all stop for a while. The engine will run for up to a minute with no noise at all, then one (or both) of the little drummers will start up again.

Can lifters be this noisy? Or is it something else, like sticking pushrods perhaps?

Again, I'd like to empasize that the noise only starts as the engine reaches operating temperature and is never present when its cold or warming up.

Engine performance doesn't seem to be affected -- the motors idles and runs pretty well regardless whether the noise is there or not. I'm not seeing any blue or black smoke. I do see white smoke (or is it condensation?) until the engine is at operating temperature.

I've put about 600km (~350 miles) on the truck since I got it. I'm running 15W-40 oil with a quart of ATV, and I've change that out once after about 300km.

 

You mentioned that the noise stops for a minute then starts again. You put ATF in the oil for the detergent i would think. You may have stirred up a bunch of trash. This may be getting into the oil pressure relief valve and dropping your pressure at idle to the point you hear valve train noise. You may be looking at pulling the pan and cleaning out a bunch of trash. I personally don't like harsh cleaners for that reason. The detergent in good quality oils will do the same job but do it slow enough that the particles will be very tiny and not get caught anyplace but the filter. Good luck.

 

You're probably right.

When I first got the truck a couple months back it was running on straight oil (to the best of my knowledge) and the noise was constant then at operating temperature. Since I've been using a heavier oil with ATF and put a few miles on it I get periods of noise-free operation, which seems to be an improvement.

I can't really associate the presence of noise with oil pressure or engine speed. It will come and go when the truck is left to idle. It will come and go when accelerating up a long grade at 40-50 mph, or coasting down the same grade. Doesn't seem to matter what the engine is doing.

I do a lot of short-haul driving (5-10 minutes then shut off for a couple hours or more) so the engine is running cool much of the time. Perhaps some longer hauls might be beneficial.