4.0 knock on start up

black oil ^

ok so this is how black my oil is after 1 week...

i've got a knock on start up. nothing loud, can't hear it if i rev it over idle. goes away after i drive it for a bit. i've read everything from it could be a sluge problem blocking the oil pump (my oil pressure is at about 50psi about 1 second after start up), oil drain back valve problem ('01 XJ block has a horizontal mounted filter so it doesnt completly drain), piston slap (whats that? i read it's nothing to worry about), and it could be noises from the lifters but i herd that wasn't a bad thing either.

runs smooth, just changed spark plugs.

engine light is on for (one code for all the following): large evap leak, large oil leak into the header (or something don't remember exactly), cat failure due to possible misfire, and piston ring failure.


ideas?

doesn't sound like its gonna throw a rod it's not consistent knocking and it's not that loud

you may have piston slap. i have a 96 with 212k. it has piston knock on start will last till about 120 degree engine temp.very comon on the 4.0 with lot of miles.

My guess is that code is for an evap leak. Take it to advanced auto and scan it. As for the knocking on start up, I've got the same problem at 160k. Not sure whats causing it but would love to know.

BTW does that oil smell like gas?

Piston slap is more than likely the culprit. As for the evap code is it a PO455 or 456? That could be either a bad gas cap to a crack in one of the hard lines or a split rubber line running off your evap. Check the lines. Never heard of a code for piston ring failure or oil in header....

Can't hurt to check the torque converter bolts if it's an automatic.

I'd stick with the oil quality. Is it thin (low viscosity)? How much drains at the change? Have you recently changed the engine to the '01 block? If so, did you have it checked for cracks? I'm shooting blind, but you shouldn't have black oil after a week. Whatever is causing that symptom is assuredly causing the knock.

Your profile says 2001 XJ (we shouldn't have to guess or look up that bit of info :lecture: ).

What is the vehicle's maintenance history? Recently new to you?

Black oil within one week I would say your engine has sludge buildup in it from lack of maintenance and/or running too cold.

Is the engine reaching normal operating temps--205~210 degrees?

Have you considered using a diesel engine oil--they are highly detergent and will clean the inside of your engine very well. You would still get dirty black oil until things are cleaned up.

Are you using a quality oil filter with a silicone drain-back valve instead of the failure prone nitrile rubber valve?