I changed the oil in my Rig today. The local Advanced Auto was running a special on royal Purple so I figured I would give it a try. This is the first time I have changed the oil since I bought it. I have no idea what the PO ran. I put about 1/2 a quart in the filter and 5 1/2 in the engine. After i was done I heard a slight knocking sound that I didn't hear before. Any thoughts?

 

it usually means the guy you bought it off of knew about the knock so he put a heavier weight oil in the engine to quite it down until he sold it to you...

 

That would SUCK!! I did finally measure What I took out and I took 5 Qt. out and put about 6 in so I am heavy. Would this cause the knock?

 

The 4.0 calls for six qts so you were light b4

 

Would the knock come from running a synthetic when there was probably a conventional in there before?

 

I agree with Cherokeefreak... The po probably used a much heavier oil in it to artificially boost the oil pressure, and to possibly mask some other noises- knocks, ticks, etc. Synthetic oil has smaller molecules than conventional oils so it is "slipperier". A lot of times if you put synthetic oil in a high milage engine that has always been running conventional oil, it will blow though seals and gaskets that were kept swollen by the conventional oil, and you will discover many new leaks and weeping that weren't there before. It can also find its way through the oil pump, and bearings faster which can cause a slight drop in pressure, You may want to put in an additive that is compatible with synthetic oil, at least that way you may be able to keep running that very expensive royal purple.

Corey

 

The Oil Pressure at Idle right now is at about 50. Not sure if that is high or low. When I took the oil cap off to add the new oil there was a small white piece of something stuck to the cap. I don't know a whole lot but I know that is not normal. 6 Quarts is recommended for a 4.0 so should I just put in an additive or do some kind of engine flush. Any recommendations on That?

 

What color was the oil when you drained? How long did you go before changing the oil after purchase? If the oil was black and smelt like burnt oil, even with a heavier weight, you would have heard the knock prior to changing. And even then, a fresh oil change with a heavier weight will not always quiet down a knock. Now this is just my experience from building honda engines for 8 years.

 

I drained the oil in a clear container and It looked like coffee, very dark. It did have a slight burnt odor to it but not bad. I drove it about 1000 miles before changing it. The knock was new after the oil change. Should I just do a flush and see if that helps?

 

A flush may or may not help. Its hit or miss. Does it knock at all times? Or is just when you first crank it up? Did you see any metal shavings in the oil that was removed?

 

I did not see any metal shavings in the oil and the knock in constant, but seems to diminish once it is started but this may just be me hoping that it will go away.

 

A slight Knock on start up after a Oil change is Normal for high mileage engines. My Chevy does it and my Taurus.

Also if you listen closely alot of engines have a little Knock on start up till Oil pressure comes up. This is from worn bearings......

 

This just happened to me. I swapped in a new motor, 80 grand on the clock. It ran great, I had about 500 miles on the motor with NO knocks. I wanted to change the oil again so I could flush it, and see how things looked. Old oil looked great. I put royal purple in, and not even 10 miles after the change, it had a slight knock in the bottom end. I put about another 15 miles on it, and then changed it to 15w-40 diesel oil. It still knocked for about the first 5 mins, but after taking it out and gettin on the throttle a bit, I came back and the knock was mostly gone. If you listen closely, its still there. We will see how it recovers, but the RP Deffinatly did her in, as the motor is in good condition.