1989 Jeep 4.0 Rod knock

[mstrjon32]

Originally Posted By: wjli
I think you have it grease monkey. Now you are faced with the uncertain dilemma-----Is there an oil/filter combination to stop it?????


I ran PureONE's on my 4.0 for a while, but it did quite a bit of slapping with them. I went back to Mopar filters and it's quieted down significantly. I don't care what the flow charts say.

 

[addyguy]

If the noise went away as the engine warmed up, its almost certainly piston slap - it goes away as the piston heats, expands, and fits the bore.

A little thicker oil (10W-40) might quiet it down a bit, but for the most part, you just live with it. I speak from experience - I drive an 02 Cavalier that does it all the time, and I might try a 10W-40 at some point to see what it does....

 

[Greg L]

I had valve tick the first time I switched from PP to Havoline in my 4.0 Jeep.

Put a bottle of Valvoline Long Life moly additive & it went away.


Your problem doesn't sound like a quick fix, though.


GL

 

[Greaser]

If you have a knock at idle and it goes away with more RPM thats piston slap.If it gets louder with rpm you have rod or wrist pin issues.If you have a knock under load thats a main bearing problem.The 4.0L has alot of weird noises and 90% of em sound like a diesel at idle but quiet up under acceleration...normal 250,000 miler.There was a piston skirt increase in the later years that quieted things up greatly.As for skirts being found in the bottom of pans I have not heard of a slew of 4.0's having this problem.I have found that the 4.0L engine runs quieter on a thicker 30W or a 40W HDEO like Delvac 1.My Cherokee had a knock new with 1500 miles on her.Have 272,000km on it now and it runs better than ever.My Wrangler was always very quiet from new till now with 208,000km and runs strong and never uses oil.Both using HDEO and my UOA's show that they are both running clean and have low wear numbers.

 

[grease_monkey]

Originally Posted By: Greaser
If you have a knock at idle and it goes away with more RPM thats piston slap.If it gets louder with rpm you have rod or wrist pin issues.If you have a knock under load thats a main bearing problem.The 4.0L has alot of weird noises and 90% of em sound like a diesel at idle but quiet up under acceleration...normal 250,000 miler.There was a piston skirt increase in the later years that quieted things up greatly.As for skirts being found in the bottom of pans I have not heard of a slew of 4.0's having this problem.I have found that the 4.0L engine runs quieter on a thicker 30W or a 40W HDEO like Delvac 1.My Cherokee had a knock new with 1500 miles on her.Have 272,000km on it now and it runs better than ever.My Wrangler was always very quiet from new till now with 208,000km and runs strong and never uses oil.Both using HDEO and my UOA's show that they are both running clean and have low wear numbers.

I did an old diagnostic test my grandfather told me about and from the way every thing is adding up it is a safe bet that it is piston slap. now if i can just convince my brother in law to run a thicker oil.

 

[Greaser]

If you look at the coolant flow on the 4.0L straight six it comes in at the front cylinder and goes out the back.Most of the noise comes from the front cylinders.I've read that several bore measurements on various 242's with lotsa miles have shown the first 1 or 2 cylinders to be actually ob-long or oval,not round like the ones out back.Why this occurs?Piston slap due to coolant flow,timing design,piston skirt length who knows?But an old 4.0L that sounds like a diesel at idle is pretty normal...we have alot of em' in different heaps at my Jeep club.

 

[Dupree]

the jeep 4.0l are notorious for piston slap with certain oils, they can be really noisy beasts

 

[FastSUV]

My '01 Grand Cherokee sure seems quiet??? It doesn't sound like a diesel nor do I hear anything abnormal...Should I consider myself lucky?

I have been using Trop-artic 10w30 blend. I have wanted to try a 10w30 diesel oil but was worried about my emissions system since it is a CA emissions vehicle and O2's & cats are not cheap...it doesn't seem to use a significant amount of oil so maybe I could get away with it?

 

[Greaser]

The newer models were very quiet.They got it near perfect then canceled the engine model....like so many before it.

 

[BuickGN]

I didn't read through this thread but when I had a true rod knock and not enough money for a rebuild, I tried several thick oils and Valvoline straight 60wt made it the quietest, signifigantly quieter than the 20w-50 oils that I tried.

Just had to be careful on a cold start, if rpms went above 1,200 it would blow the filter off with the guage pegged at 120psi. Made it through a year though.

 

[BigJohn]

Our '89 4.0l with 170,000 miles has the 'diesel sounding' knock as well. We have done a couple of things....

First, the oil pressure wasn't what it ought to be, so we dropped the oil pan and put in a new oil pump. That helped the pressure, but the knock continued.

We tried synthetic oil in a 10w30, but it only helped when the oil was new. As the oil got some miles on it, the knock came back.

Also tried 20w50 and it really helped, but just couldn't bring myself to using that oil in the winter....and have had 5w30 in it, but the knock continues...especially at start-up idle.

For this summer, I think we are going to give a 15w40 Diesel oil a shot, or maybe 5w40 Rotella synthetic.

 

[Greaser]

In an older 4.0L I would use a HDEO in the 15W-40 flavor for warm weather and a HDEO in the 5w-40 weight for colder weather.Synthetic or Dino it's up to you and even a mix is great.Some of the thicker 30 weight oils are good too.I'm just a fan of the HDEO's due to the concept of more additive package to compensate for fuel,coolant,tolerance issues in older engines.Geritol for older,graceful engines so to speak

 

[Greaser]

Originally Posted By: FastSUV
My '01 Grand Cherokee sure seems quiet??? It doesn't sound like a diesel nor do I hear anything abnormal...Should I consider myself lucky?

I have been using Trop-artic 10w30 blend. I have wanted to try a 10w30 diesel oil but was worried about my emissions system since it is a CA emissions vehicle and O2's & cats are not cheap...it doesn't seem to use a significant amount of oil so maybe I could get away with it?
Most of the current HDEO's are SM rated now.Which means a lower ash and ZDDP content so the cats are safer than ever.