1993 Engine Knocking

1993 k1500 5.7L, 189,000 miles, orig engine and tranny. This vehicle is a recent purchase, after a new filter and oil change with Mobil 1 5w-30, and new transmission filter and fluid change with Dex III, the engine has a slight knock. All fluid levels have been rechecked and are correct. The knock is only audible when sitting in gear and after the engine warms up considerably. Is this just the sound of an old engine or is it something else? Thanks in advance.
-Mike

Does it sound like a hammer on metal, or more of a click? The hammer noise could indicate a bad connecting rod bearing, while the click could be a bad valve lifter. Does it make the noise when in PARK? If not, it could be a tranny problem. I know this sounds vague, but until you can isolate the noise, it will be difficult to diagnose.

5W-30 is a little light for a motor with that many miles, I have a '94 with 198,000 miles on it, I use 15W-40. What is your oil pressure when warm?

If you are inclined, and have the time, pull the oil pan and check the bearings. It will take most of a day, but you'll know what's up. The only real solution to a bad rod bearing is to remove and rebuild the crank and put in new bearings. A sticky valve lifter might be cured by trying a solvent rinse of the motor while idling. If that doesn't work, removal and replacement is called for. If the noise is coming from the tranny, it could be the torque converter.

U-235,
Thanks for the reply. It sounds like a click, and the noise is considerably quiter when in park, but you can still hear it. I just don't understand how an oil change could make the engine knock. Maybe the guy used a heavier oil? I'm not sure what the oil pressure is at idle, I think its 35psi and at Hwy speeds 60psi its moving around with engine rpm's Does the 15w-40 help with older engines? I also used a synthetic oil, don't know if that matters either?

The tranny seems to shift fine and I have not noticed anything coming from that area seems to be coming from the engine.

What is the product to clean the lifters and how do I go aobut doing it?

Another trick is to pull one plug wire at a time with the engine running. If you have a bad connecting rod the effected cylinder will be very apparent with the plug wire disconnected. The lack of combustion in the cylinder does not allow any wear or slap of the rod to be absorbed and therefore it will be very loud compared to what you hear under a combustion load. However, based on what you are saying about a click rather than a knock, I doubt it is a connecting rod, but it is one more thing to eliminate. "GUNK" makes a motor flush additive you can use. It comes in a quart can an is added directly to the oil. But you need to drain a quart prior to adding it. Good luck.

U-235,
Thanks for the reply. It sounds like a click, and the noise is considerably quiter when in park, but you can still hear it. I just don't understand how an oil change could make the engine knock. Maybe the guy used a heavier oil? I'm not sure what the oil pressure is at idle, I think its 35psi and at Hwy speeds 60psi its moving around with engine rpm's Does the 15w-40 help with older engines? I also used a synthetic oil, don't know if that matters either?

The tranny seems to shift fine and I have not noticed anything coming from that area seems to be coming from the engine.

What is the product to clean the lifters and how do I go aobut doing it?

The oil pressure looks okay, maybe even a little high. My oil pressure, if 5W-30 is used, almost doesn't register when warmed up at idle, but with the 15W-40 it runs 20 to 50 psi. Please note your engine may have different wear in it compared to mine, just throwing out ideas. If its a click, I would suspect the lifters, try the Gunk stuff, I use it at every oil change, DO NOT DRIVE AROUND WITH IT IN THE OIL!!! You just add it to the crankcase before changing the oil. I have my Sub warmed up and leave the Gunk in for around 10 minutes at idle. I like it because it thins the oil out and lets it drain more readily.

If you want, call the previous owner and ask what weight oil he ran. Its been my experience that V-8's require a minimum of 10W40, especially when they have high miles.

If the noise doesn't go away, bite the bullet and pull the intake manifold off, remove the lifters and clean/replace them. Don't keep using oil additives that you need to leave in, you'll just mess things up more and waste your money. Try a mechanics' stethoscope if you have one, or a long screwdriver, place around the intake manifold while the engine is idling (BE CAREFUL...MOVING PARTS :biggrin: ) and listen to see if the noise is amplified.

As long as you are maintaining the oil level and oil pressure, don't worry too much. Take your time and diagnose the problem correctly, or have a reputable shop do it.

U-235,
Thanks again, I will try those things and then go from there.
-Mike

Hello

I have a 95 with a 5.7 and have run nothing in it but Mobil1 syn 5w30 my self and have 193000 on mine and its my daily driver and warm at idle in drive i have 35psi, and i do pull a 28ft boat in the summer. But just a suggestion as the other guy did, i have always run 1 qt of rislone in place of a qt of oil at oil change in anything i've owned that has had a sticky lifter. The reason i do is because you run the rislone all the time. With the other since i read its a recently new veh to you you dont know how it was taken care of, and the gunk could (and the only reason i say this is because i've been a mechanic for 23yrs and have seen it happen..not that it will) break enough varnish and sludge loose to plug and or block off some of your oil passage ways in the eng and cause oil starvation to vital eng parts. And the rislone is more of a slower less dramatic cleaning of the varnish and sludge. I agree with the other guy about pulling the intake and maybe the pan. If you do pull the pan and every thing is ok PLEASE BUY A NEW OIL PUMP even if you replace noting else, a quality pump should'nt be more than 40 bucks.But a like i said just my two cent worth.

Changed the oil from 5w-30 to 20w-50 and noticed a much quiter engine, the oil pressure is up to 60psi when cold and around 35-40 when warm. Before the oil change it was 40 cold and 20 warm, the engine sounds better and the kock is only barely audible. Would it still be the lifters?