Two months ago, I asked about the well known "4.0 Rattle". The reason I asked was because my new to me 00 WJ didn't. I just changed the oil, and now it does! It had 2800 miles on a 10W30 conventional oil which I changed to Valvoline Max-Synthetic 5W30. Change was at 130K. My oil pressure is actually higher both hot and cold, but the rattle came on at startup.

I'm not concerned about it. I am just amused that it wasn't there before the oil change and was there after! Makes me wonder what the dealer put in the oil to silence it!!!

 

What filter did you use?

 

I'd go back to 10W30 oil. I'd never run 5W30 as it's too thin, IMO.

Some oil filters don't have an anti drain back valve built into them, so they're empty upon start up, causing no oil to the bearings and the noise lots of people hear. Once they fill up, oil then passes on to the bearings and the rest of the engine, and the noise goes away. A pressure gauge might not always show this, but an idiot light will. That's why I like the light as a back-up. Lots of people stop looking at their gauges over time until it's too late, but that light will usually catch their attention.

 

I ran 10W-30 for a year in my 1994 4.0 H.O. in my last jeep, then switched to 5w-30 Mobil one full synthetic, and the lifters got a little bit noisier because of the thinner oil. It ran from 230k to 250k like a champion on that full synthetic, and was as clean as it ever was because of it. Was a good switch for me.

 

Look guys! I've got NO problem with the noise! It is inherent with this motor! I just found it amusing that it started after an oil change. You are right, 5W30 is thinner than 10W30 WHEN COLD!!!! It still maintains lubricity of a 30 weight oil at operating temps. My oil pressure actually went up!

I've used Valvoline oil an all my vehicles since 1965 and NEVER HAD AN OIL-RELATED PROBLEM!! I also lived in Cranston, RI, right next to the FRAM factory and also never had a filter problem!

You guys go on and on about what oils and filters are best! The only oil I never liked was Texaco Havoline because to actually smelled bad! I worked for Texaco, but I never used their oils. It got warm and gave off an odor like it was burning. It also turned dark quickly.

You want an oil that is superb? Aero-Shell Aviation Oil. It's expensive, but it will clean out your engine like a kerosine wash! I've seen sludge come out like diarea!

We have also used accumulators to hold pressurized oil after shutdown, on drag cars and boats, so that the bearings are flooded with oil before lightoff. But that's going to extremes.

 

Coming from race cars to this Jeep that rattling scared the **** out of me all I could think of was damn an engine rebuild and no cash. Ive learned over the years of having my 04 if its noisy clunky and loud its fine. Its when the dummy lights come on that there is a problem.

 

There you go! Sounds like a thrashing machine, but runs strong! This motor came from AMC (American Motors) and people wouldn't buy the cars because of the noise. It found a home in Jeeps, though.

Hey Blue! Did you know my wife drove 15 miles back home because the oil light was on??? The motor was toast!!

 

Gentlemen! (I use the term very loosely) I just got a shock! The Jeep 4.0 is NOT the old AMC motor! It's an upgrade of the Wrangler I4! I feel a lot better now because I never liked AMC. Even the Eagle was a piece of junk.

Live and learn!

 

The 4.0L is actually based off the AMC design, and many people use the AMC crank/rods and new pistons to build a stroked, more powerful version of the 4.0L when it's time for a rebuild.

 

^This. The 4.0 is based off the AMC 4.2L

And it's a damn good platform as well. I know you said you've excepted the noise, but there are things you can do to minimize the lifter tick and piston slap. Just my $0.02

 

I don't have piston slap yet. It's just a mild lifter tick. If I bring it up to about 1500 rpm, it's gone.

 

I would be pissed if my gf or wife drove the truck home with the oil light on wtf. Good thing for those cast iron heads. The noise sucks and if you go to 5w it leaks like a bytch so I went back to 10w now it leaks normally. I just like knowing that if the Jeeps hit a snag they still run and can get you home most cars and suv's these days just give up on you even if a sensor dies.

 

That was my Chevy small block she drove 15 miles with no oil pressure, not my Jeep! It only had about 1 1/2 gts of oil in it.

Although I dearly loved that woman, she grew up in Brooklynn and didn't get her liscense until 26. She said she thought it just needed oil. After I calmed down, I told her if that light comes on while you're driving, turn the motor off ASAP. She apologized, but I still had to rebuild my truck, taking her van to work while I did it. If you really want to **** off a woman, clip her wings!

Having grown up in the cockpit of an airplane, I constantly check my guages. Not many people do. Seems to me, manufacturers could give you an INTENSE warning when something is wrong. Not just a small light that says "check guages". Remember GM's "HOT" light? How hot is it? Dunno. How about shutting the engine off when oil pressure drops below 10 psi or temp gets above 250 F? They won't because they want to sell you a new car!

My whole point is this. The 4.0 is strong and reliable but you still have to take care of it.