Why does my 93 sound like a diesel?!

[tireroastin93XJ]

It's a 4.0 auto with 135,000 miles and has always sounded like that since I've had it. It only sounds like that at idle. At cold start up it sounds normal, but after running about 20 seconds it sounds like a diesel. Any thoughts? It's really starting to annoy me!

Thanks
Mike Harris

 

[logdog]

Try a higher octain gas. (bad guess)

 

[Dr. Dyno]

It sounds like your 4.0 has the same affliction that's common to most 4.0's, and that's cold start piston slap. Once the engine warms up and the pistons expand in the bores, the noise eventually goes away. It's more of a nuisance than a problem. It doesn't seem to cause higher oil consumption or reduce the life expectancy of the engine so don't worry about it.
There's two things that you can do that might reduce or eliminate the noise. One is to run some Mopar Combustion Chamber Cleaner through the TB to clean out the carbon deposits from inside the engine. The other is to drain the engine oil and flush the crankcase with engine flushing oil. If the engine's never been flushed before, you'll be shocked at how much black grunge will be washed out but amazed at how much smoother and quieter the engine will run afterwards. Gas mileage might also improve. Give it a try.
_______________________________________________________________
- 1992 4.0 XJ Laredo with mods - 174k miles - AX15, NP231, D35c, D30
240hp@5250rpm/280lbft@3500-4000rpm, 1/[email protected], race weight 3465lb
- 4.6L STROKER almost ready to install
- Websites - Jeep 4.0 Performance, 4.6L Stroker Build-Up, Dino's Jeep Tricks

 

[tireroastin93XJ]

It sounds like your 4.0 has the same affliction that's common to most 4.0's, and that's cold start piston slap. Once the engine warms up and the pistons expand in the bores, the noise eventually goes away. It's more of a nuisance than a problem. It doesn't seem to cause higher oil consumption or reduce the life expectancy of the engine so don't worry about it.
There's two things that you can do that might reduce or eliminate the noise. One is to run some Mopar Combustion Chamber Cleaner through the TB to clean out the carbon deposits from inside the engine. The other is to drain the engine oil and flush the crankcase with engine flushing oil. If the engine's never been flushed before, you'll be shocked at how much black grunge will be washed out but amazed at how much smoother and quieter the engine will run afterwards. Gas mileage might also improve. Give it a try.
_______________________________________________________________
- 1992 4.0 XJ Laredo with mods - 174k miles - AX15, NP231, D35c, D30
240hp@5250rpm/280lbft@3500-4000rpm, 1/[email protected], race weight 3465lb
- 4.6L STROKER almost ready to install
- Websites - Jeep 4.0 Performance, 4.6L Stroker Build-Up, Dino's Jeep Tricks

It doesn't sound like that at cold start up, it sounds fine. It starts making the noise about 20 seconds after starting, and when it's warm.

Mike

 

[89MJComanche]

The other is to drain the engine oil and flush the crankcase with engine flushing oil. If the engine's never been flushed before, you'll be shocked at how much black grunge will be washed out but amazed at how much smoother and quieter the engine will run afterwards. Gas mileage might also improve. Give it a try.[/color]
- 4.6L STROKER almost ready to install
- Websites - Jeep 4.0 Performance, 4.6L Stroker Build-Up, Dino's Jeep Tricks

I have a different opinion about the above statement. Engine flush is not a good idea. The best way to clean out is to drop oil pan and wash it out, remove valve cover and clean it out. Re-install both, and run some high detergent synthetic through the engine changing oil about every 1000 miles for 3000 miles.

Engine cleanout oils remove more than just oil deposits. They remove the gunk from the places where there are gaskets and seals that keep your engine from leaking. In my experience engine clean out oils cause oil leaks!! Then again if you are going to drop the pan and remove the valve cover you only have one other gasket, the head gasket.

Replace the rear main while the oil pan is off.... then run semi synthetic like Valvoline Max Life. It works just as well as the $5/qt stuff.

My oil looks like Golden Brown Maple Syrp after 3000 miles. As a matter of fact I re-use my XJ oil in my MJ for the past three years. THE MJ is a work truck only and it has changed its own oil one drop at a time for the past 4 years!! 250K on it.




AARON

 

[jneary]

the majority of the jeeps from aruond that year or so make that noise,chrysler says it is o.k. at first they wanted us to measure cylinder bore and order pistons to match but never fixed the problem. then they said it was the material on the piston skirts causing this, however ther is nothing related to this that can cause engine failure. if i remember correctly chrsler wuold offer the customer either a new engine or extend the warranty to 70,000 miles. dont quote me on that though, i cant remember the details. but thas shows their confidence in the engine. i would bet if you took a pole, everyone would say the 4.0 engine is by far the best engine ever put in any jeep.

 

[Atl XJ]

Yeah, mine's been doing that since 70K miles and although it sounds like a piece of junk my mechanic told me exactly the same thing that Jneary said. Something about the piston skirts and not to worry about it, it'll run 100K miles like that. He was a Jeep mechanic for 20 years so I trust his judgement on that. I'm at 92k now and it hasn't caused any issues so far, knock on wood. I really wish there was a fix for it though becuase it annoys the crap out of me. I usually just turn on the radio or kick on the a/c. You can't hear it over the electric fan.

 

[jneary]

or get another motor. but if it is noisy too.......

 

[jneary]

or you can get a new motor, but if it makes the same noise.......
just drive it and enjoy

 

[Dr. Dyno]

I have a different opinion about the above statement. Engine flush is not a good idea. The best way to clean out is to drop oil pan and wash it out, remove valve cover and clean it out. Re-install both, and run some high detergent synthetic through the engine changing oil about every 1000 miles for 3000 miles.

Engine cleanout oils remove more than just oil deposits. They remove the gunk from the places where there are gaskets and seals that keep your engine from leaking. In my experience engine clean out oils cause oil leaks!! Then again if you are going to drop the pan and remove the valve cover you only have one other gasket, the head gasket.

AARON

I've twice done the engine flush treatment on my 4.0 without any problem, and the flushing oil did NOT induce any leaks. High detergent synthetic would certainly do that though.
Whether or not it's a good idea to use flushing oil depends on how much contamination there is inside the crankcase. Mine doesn't have any sludge at all, only the usual oil contamination, so the engine flush worked for me. My engine has minimal cold start piston slap and sometimes none at all.
Engine flush will not clean out sludge though and if you use synthetics or anything else with high detergent content, bits of sludge can break off and block the oil pump pick up screen, oil passages, and cause valve lifters to stick. Even cleaning the inside of the oil pan and valve cover might not be enough for a heavily sludged engine because all the internal engine parts will be coated with it. The only cure in such a case is to completely strip down the engine, clean everything, and rebuild it.

 

[tjl1388]

Mine sounds like a diesel as I shut it off. As the engine shuts down, it sounds like a diesel.....clunk clunk clunk. Is that the same thing?

 

[Sarge]

I have a different opinion about the above statement. Engine flush is not a good idea. The best way to clean out is to drop oil pan and wash it out, remove valve cover and clean it out. Re-install both, and run some high detergent synthetic through the engine changing oil about every 1000 miles for 3000 miles.

Engine cleanout oils remove more than just oil deposits. They remove the gunk from the places where there are gaskets and seals that keep your engine from leaking. In my experience engine clean out oils cause oil leaks!! Then again if you are going to drop the pan and remove the valve cover you only have one other gasket, the head gasket.

AARON

The flush doesn't CAUSE leaks. It may reveal leaks already in existence and so should the high detergent oil. If the oil doesn't then it aint doing its job. My personal method would be to drop the pan and clean; remove the valve cover and clean; then flush.

Sarge

 

[burntkat]

yup, completely normal- my 90 XJ does it and so does the wife's 94 ZJ.

regarding cleaning- just run some synth through her as mentioned above <every 1000, for 3000>-- it'll do just fine.

 

[Atl XJ]

Mine sounds like a diesel as I shut it off. As the engine shuts down, it sounds like a diesel.....clunk clunk clunk. Is that the same thing?

Mine used to do that and it was the catalytic converter going bad.

 

[tireroastin93XJ]

Thanks for all the replies! Guess I won't worry about it. The motor is very strong and runs like a bat outa hell, it's just annoying at idle. Like I said, it doesn't do it at higher rpm, at least if it does, I can't hear it. I thought I read something about 92-94's having a piston noise in them in JP or another mag doing an article on which XJ was the best to buy. I agree with pulling the pan and valve cover and cleaning before doing an engine flush, that's a good idea. I change my oil every 3000 miles, don't use synthetic, I use Quaker State, since that's what the previous owner used, and the oil isn't very dark at all when I change it, still looks pretty good and isn't low. I've been lucky and haven't had any oil leaks yet. And at 133,000 miles, I'm expecting some.

Thanks again!
Mike Harris

 

[RichP]

Well, my opinion, I wouldn't touch quaker state with someone elses money, not in my vehicles. My 98 is fast approacing 200,000mi, made the change to Mobil-1 around 5,000mi or so and since then there has been nothing else in it except for a 'field oil change' at paragon after it got dunked at around 50,000mi crossing a lake, it got 6 quarts of Mobil 10w30 organic and a new filter. The synthetics will provide very high detergent cleaning whether it's Valvoline, Castrol, Mobil or Royal Purple, etc. The main difference is that they are a bit more gentle than the flushes and take a few thousand miles vs 15 minutes. Down side is that once you put that flush in there it tends to soak into the sludge and keep working even after you drain the oil and refill so you still need to keep an eye on the oil color and change the filter when you can't read the hash marks on the dipstick. The same is also true when you change to a synthetic oil, it starts cleaning. If the filter plugs up then a bypass in the oil system kicks open and you get unfiltered motor oil circulating.
If you are going to run a flush like 'Motors' thru it I would do the flush first before dropping the pan or lifting the valve cover, though I suppose it would not hurt to clean both ahead of time, kind of a headstart so the cleaner does not have to work on the heavy stuff. When you do lift the valve cover keep a shop vac in one hand and a plastic scraper in the other, use the vac to catch any pieces of sludge that break free befor they can work their way back into the returns othewise the crud can block the pickup to the pump, lost a 2.8 that way when I was trying to seal an oil leak from the back of the intake manifold. The flushes and synthetics won't break big chunks loose like manually removing the crud.

 

[tireroastin93XJ]

Well, my opinion, I wouldn't touch quaker state with someone elses money, not in my vehicles. My 98 is fast approacing 200,000mi, made the change to Mobil-1 around 5,000mi or so and since then there has been nothing else in it except for a 'field oil change' at paragon after it got dunked at around 50,000mi crossing a lake, it got 6 quarts of Mobil 10w30 organic and a new filter. The synthetics will provide very high detergent cleaning whether it's Valvoline, Castrol, Mobil or Royal Purple, etc. The main difference is that they are a bit more gentle than the flushes and take a few thousand miles vs 15 minutes. Down side is that once you put that flush in there it tends to soak into the sludge and keep working even after you drain the oil and refill so you still need to keep an eye on the oil color and change the filter when you can't read the hash marks on the dipstick. The same is also true when you change to a synthetic oil, it starts cleaning. If the filter plugs up then a bypass in the oil system kicks open and you get unfiltered motor oil circulating.
If you are going to run a flush like 'Motors' thru it I would do the flush first before dropping the pan or lifting the valve cover, though I suppose it would not hurt to clean both ahead of time, kind of a headstart so the cleaner does not have to work on the heavy stuff. When you do lift the valve cover keep a shop vac in one hand and a plastic scraper in the other, use the vac to catch any pieces of sludge that break free befor they can work their way back into the returns othewise the crud can block the pickup to the pump, lost a 2.8 that way when I was trying to seal an oil leak from the back of the intake manifold. The flushes and synthetics won't break big chunks loose like manually removing the crud.

Thanks for the advice, I've been wondering if I should switch to a synthetic or not considering the mileage. I've also been reading other posts here about the very subject and how the synthetics can cause oil leaks. I'll probably pull the valve cover and pan and clean them then use the sythetic. Like I said, after 3000 miles my oil isn't that dark at all, it really surprises me. I would think if it had a lot of crud in it, the oil would be darker.

Mike

 

[RichP]

In the case of QS I'd be more prone to believing it's leaving all around the engine instead...

 

[tireroastin93XJ]

Thanks for all the replies! I was listening a little closer to my engine and it sounds like it's mostly coming from the top like valve train noise. Do the rocker arms ever need adjusting like on Chevys or do they need replacing?

Mike Harris

 

[RichP]

Thanks for all the replies! I was listening a little closer to my engine and it sounds like it's mostly coming from the top like valve train noise. Do the rocker arms ever need adjusting like on Chevys or do they need replacing?

Mike Harris

Generally the hydraulic lifters clog up and don't fill up or expand all the way, thats one of the things an engine flush will do, dissolve the crud in them. Synthetic motor oil on the other hand never lets it build up with to start..