I would go into the ask a question section, but for some reason my browser will not let me in. I am not sure if this is a common problem or not.

I have an older jeep and I am running heavy oil in the 4.0L motor because it has wear issues. The motor sounds okay when cold and when running cold. After it warms up I start getting a kind of hissing sound. In the expectation that it is not a good thing, I use the noise as a shifting point. (It is a Cherokee with a 5 speed).

I would describe the sound as what a room full of sewing machines would sound like. A kind of mechanical clicking that occurs so frequently as to be almost a hissing sound. I was thinking that it was the collective chatter from a motor with excessive clearance in the valve train, but when I look into the oil filler hole, it would appear that the rockers are non adjustable. The noise gets progressively louder with RPM and it limits my ability to accelerate away from a stop.

I was thinking about dumping a can of "Sea Foam" motor cleaner into the oil and see if that helps. Anybody have any ideas about this?

John

 

Check for exhaust leaks, particularly in the exhaust manifold where the collector is.

 

Oh...what part of Wisconsin are you in? There are several of us in WI.

I'm in Milwaukee.

 

I live in the Green Bay area, in the direction of Manitowoc.

 

While Seafoam is great in your gas tank or intake it's not really the kind of crap you want to put in your oil. I would recommend Rotella 10-40, Wix or Napa Gold oil filter, and a quart of MMO.

 

Most older 4.0's sound like a diesel-powered Singer sewing machine. They are not a quiet engine.
The devil is in the details though, there are 'normal' 4.0 noises and there are 'trouble' 4.0 noises. Easiest way for us to take a shot at which you have is if you could post a recording of the noise.

You said the noise was limiting your ability to accelerate. Is that because you stop accelerating when you hear it or is there something holding the engine back?

What is your oil pressure at hot idle? How about while driving?
What weight oil is in there and what sort of filter?

 

I have no easy way of getting the sound of the motor on the internet. A little more background on the inline six motor.

The motor burns some oil, there is some blow by coming from the crankcase vent, but oil usages in not enough to interfere with running. The spark plugs look pretty good generally. Also the oil pressure light comes on at idle once the motor warms up. I put straight 30 weight in the motor. (had it on hand)I think the filter is a Fram or some low cost equivalent purchased locally. Given the oil pressure drop, no doubt the lower end is loose.

The motor starts and runs just fine at low to moderate RPM. Also it is quiet at low RPM. Once a little warm, a couple of miles, the red light comes on at idle and I get a metallic hashing sound at medium RPM. It will come and go with the throttle position. Step on it hard and it gets noisy fast, more noisy when pulling. There is a power decline, but that may be the normal power curve.

The warmer the motor gets, the lower the RPM where the noise starts. It interferes with my driving only in that I shift earlier than I otherwise would, and I am reluctant to run it out hard. My newer '99 Cherokee with the inline six has yet to make a similar sound. Otherwise I am unfamiliar with the jeep 6.

I am guessing that if it were from the lower end the motor would have already blown up, and I know what piston slap sounds like. My current thinking is to just use the vehicle the way it is and hope for the best.

John

 

I would start by getting rid of that Fram (they are known to cause oil pressure problems) and putting a halfway decent oil filter on it (Wix, Purolator, Napa Gold, etc. or Motorcraft FL-1A for an oversized filter ). Straight 30W isn't great either, it is probably ok this time of year but definitely don't run it during winter (and even this time of year keep off of the throttle until it warms up). 10w30 is what the book recommends, 5w40/10w40 is also fine, 15w40/15w50 for very worn motors. Also verify the pressure with a mechanical gauge, oil pressure sending units are known for failing and if you only have an idiot light it isn't telling you much anyway.