spartan99

I have one of the few remaining warranties for Jeeps from when Chrysler included the lifetime powertrain warranty as standard 10 years ago. I am approaching 10 years and 130k miles and the engine consumes oil at a typical Wrangler 3.8 rate of half a quart or so per thousand miles. It varies but it's right around that amount. Runs perfectly fine otherwise. Is the consumption issue a matter that can be repaired under the warranty? Thank in advance.

Mark Doiron

Most 3.8s get closer to a quart per several thousand miles--six thousand in the case of mine (but it only has 218,000 miles, so I'm still breaking it in, LOL). I know it sucks, but a half quart/thousand miles is not considered "high consumption" by just about any auto manufacturer. A quart/800-1000 miles is generally considered normal.

spartan99

No biggie. I am okay with it. Just figuring I might as well enjoy a rebuild if I am entitled but if not that's okay. That's as always!!!!!!

spartan99

My only concern is that on very hot days I'll hear what sounds like pistons rattling when accelerating from a stop, or when going up a steep incline on a mild temperature day. Do you think that is from rings and/or bearings or do you think that is pre-detonation?

rob_engineer

That sounds like pre detonation, spark knock. Try this: when your gas tank is nearly empty, fill it up with 93 octane. If it is pre detonation the higher octane may make it go away. I had this in a '93 Ford Explorer. I drove it for a few years with this condition. Use 93 octane no problem. Anything less, instant spark knock.

spartan99

Thanks. I am familiar with what it but never tried fixing it before. Never come up til now. Can it be gotten rid of for good. Does my engine need be cleaned internally? Predetonation is from carbon build up on the pistonsright?

spartan99

https://www.hemmings.com/magazine/mu...l/1567737.html

Interesting article. My engine has a slight knock sometimes. Perhaps it is combustion chamber deposits like it suggests it might be.

Mark Doiron

Engine knock can be caused by a couple different things. Usually it's just poor quality gas--too low of an octane or contaminated with water. Generally, modern engines address this by adjusting the timing when they sense the knock--retarding it until the knocking stops. This hurts power output and gas mileage, but usually stops that annoying noise. Higher engine compression with lower octane gas can also cause it, and as engines age they may, in fact, become a bit tighter and have higher compression.

Anyway, technically this type of knock is not "pre-detonation". Pre-detonation is caused by some hot part in the engine cylinder that is igniting the air-fuel mixture before the spark plug is fired. It causes a similar sound, but can be caused by carbon build-up, or a part not machined properly or that has been created by engine wear (say a small piece of metal hanging at some edge that gets hot).

Carbon build-up in modern engines is mot much of a problem because gas is unleaded. That's why we don't pull our spark plugs every few thousand miles and clean them. And it's why spark plugs last for 100,000 miles instead of 10-20,000.

Having written all of that let me state right up front that my success with snake oil repairs is zero percent. That is, never have I used some additive in an attempt to take the easy way out and had it stop the problem. That's in over a half century of driving, and quite a few attempts. However, I will recommend that you try something anyway, but only because the mechanic who does the heavy lifting on my Jeep recommended it before I replace the fuel injectors that were causing a tapping noise on my own engine (post-200K miles). It didn't fix my problem, but maybe it will yours. It was SeaFoam. There are two types, one that's put in the gas (he recommended doing that twice), and one that's sprayed into the engine air intake (the fuel additive is sometimes used that way, but hydrolock is real possibility if you're not careful). You may want to try them. Again, they did not work for me, but maybe you'll have better luck.

spartan99

Good info thank you.

resharp001

There are several YouTube vids on seamfoam to watch....not Jeep specific, but interesting. Oddly enough I found myself watching this one last week for no specific reason.

https://www.youtube.com/watch?v=agAWXnT4-EQ Seems like some people swear by Seafoam, but also seems I've seen some not so great comments about it.