Jeep cold engine noise

I noticed that my Jeep has been making a distinct clapping noise any time the engine is not up to operating temperature. It sounds worst on cold mornings, but becomes quieter as the engine warms up. The noise is RPM dependent, so I’m assuming it has something to do with the engine. The noise is not audible when the engine is idling in park, but quickly shows up as soon as I put the car in gear and add gas. My father and I think that a slightly loose rocker might be the cause of the noise, but we’re not sure. A mechanic friend of his told him that our jeep has self adjusting rockers so it can’t really be fixed without replacing it. I’ve never heard of such a thing so I’m having a hard time believing it. The really confusing part is that it only makes noise when the car is in gear and the engine is under stress, making no noise when it’s just idling, even when the engine is revved. Since purchasing it 5 years ago, we have been careful to do regular maintenance on our jeep so I’m somewhat surprised by it. We really need it to the 2 more years of commuting to college so any help or advice would be greatly appreciated.

Vehicle Info:
1998 Jeep Grand Cherokee Laredo
~175000 miles
4.0L I6 with stock 4 speed transmission
Completely stock

That engine is known for having problems with the hydraulic valve lifters as it ages.
If I recall correctly, there are replacement parts of an updated design, in order to overcome this engine’s inherent valve problems.

However, only you know whether you are willing to spend some $$ on this 13 year old vehicle. If you are planning on driving it for 2 more years, I would advise spending the money–as long as everything else on the vehicle is in good shape. The good news is that the cylinder head does not have to be removed in order to replace the lifter mechanisms, so the job won’t be as expensive at it might be on some other models.

Everything else is in working order. It has a lot of miles on it but it still runs surprisingly well. My next question is whether or not my father and I could do this ourselves. If it is in fact a tedious job, we could probably get his mechanic friend to help us out too. Also, am I assuming correctly that we should just replace all the lifters, that way we don’t have to worry about the problem coming up again down the road?

For reference, my father and I have removed an engine from my Nova before and he’s done some engine timing work (with help form his mechanic friend), so we are somewhat competent.

Yes, all of the lifters would need to be replaced, if they are indeed the source of the problem.

You didn’t say how many miles on this engine, it would have been helpful to know. You could have worn out lifters, rocker arms, pushrods, or camshaft. Or it could be a combination of wear no two or more of them on any intake or exhaust. I assume this engine has hydraulic lifters so it may not be easy to diagnose until it will make noise in park but all these things are replaceable by anyone who can swap engines.

Does engine temperature have any effect on the noise?

Oldtimer, as the OP stated in the original post:
“Vehicle Info:
1998 Jeep Grand Cherokee Laredo
~175000 miles
4.0L I6 with stock 4 speed transmission
Completely stock”

Engine temperature does in fact have an effect. As the engine warms up, the noise becomes less noticeable, to the point that it can only be heard if I hit the gas harder than normal, becoming audible around 2,000 rpm or so

While I’m not sure about it, and to me it seems backwards, test the oil pressure. I may get corrected here quickly, but maybe not. If the lifters are oil filled, then oil pressure would have an impact. i would guess VDC has the best answer, but this is a pretty easy test to do. Normally (why I said it seems backwards) oil pressure will drop off a bit as the engine warms up and it flows easier, but it’s also possible that the pressure can drop, with a worn pump and thinner oil.

Just a thought to add into the mix. No, I don’t know what you’re pressure should be…sorry.

I have a habit of always checking my engine temp. and oil pressure whenever I check my speed so I’m sure the pressure is always in the recommended range, with a slight variation during acceleration of course.

I meant with a real pressure gauge, in place of the sender that’s there. The sender is just an electrical unit, and while it may be close, it won’t be actually accurate. But if you’re sure, feel free to ignore any advice given.

How would I go about checking the oil pressure, I’ve never done it before. Also, what should I be looking for and what could a pressure variation tell me?

You’d need a real pressure gauge. I’m assuming by the question that you don’t have one…I believe most major parts places (AutoZone, O’Reilly’s, etc) rent them for nominal fees. Still, you need to know what the pressure is supposed to be. Most engines (I think) run from 12-15 psi at idle, which is subject to variation.

I really wasn’t being sarcastic, although reading it I’m quite sure it appears that way. If you’re sure, feel free to ignore me - I’m used to it. Heck, I work for the Government. While I may really “be there to help”, it’s not often perceived that way.

What weight and brand oil is being used? What is the maintenance history of the Jeep? You might remove the valve cover, install anti-splash caps on the rocker arms and start the engine, watching the push rods and noting how fast they spin and those that spin the fastest can be felt for excess play. If there is excess play, remove the appropriate rocker(s), pull the push rod(s) and inspect the ends for pointing. I have seen Jeeps wear the ball on the ends of push rods down to tapered points.

Currently, I am using 10W-30 with some Lucas Oil Treatment mixed in. We have been changing the oil regularly since we got the car 5 years ago, so the service record shouldn’t be a problem. Pretty much anything that has broken or worn out has been fixed or replaced.

So where would I get anti-splash caps or is that something that can be improvised easily. Also, I’ve never actually taken any internal engine components apart, and I’m assuming that replacing the rockers requires the right torque and use of a feeler gauge to properly re-install the rockers. Would these specifications be found in something like a Haynes manual?

I just checked on a few jeep forums, particularly focusing on 4.0L engines. They say that you have to remove the head in order to remove the lifters. Moreover, they recommend replacing the camshaft and push rods along with the lifters. This is quickly starting to sound like an overwhelming project, and although I would be up for it, I feel like my dad just wouldn’t want to try it. I’m thinking at this point that we should just check and see if one of the rockers may have become slightly loose or that a push rod may have become worn out or bent. Any advice?

There are a lot of these Jeep 4.0 motors at salvage yards. Just run this motor until it quits. When and if it quits you can put a used motor in the car from a salvage yard. Just run the motor as it and crank up the stereo or put in some ear plugs to ignore the noise.

The splash caps are available at most McParts stores. I have replaced the lifters on Jeep engines without removing the heads, there is a tool made to remove lifters from their bores and they can be fished out through the push rod passages. But first confirm the cause of the problem.

Before you tear into the engine please check to see if the exhaust manifold is cracked. These are known for having the manifolds break in a weak spot, making the type of noise you describe and the noise lessens or subsides as the metal heats up, expanding and closing the crack. Just a thought.

Come to think of it several cracked 4.0 Jeep manifolds have shown up here, asemaster. And on more than one occasion they have been noisy at a cold start and gotten much quieter when hot. Hopefully that is the problem on this Jeep.