2000 Jeep 4.7L w/235000 miles. What next?

jeep
cherokee
transmissions

#1

My Jeep came equipped with the factory towing package, and I’ve done all, or almost all, of the manufacturer’s/dealer’s recommended Preventive Maintenance at the mileage mark they suggest. I switched over to a synthetic oil for the engine, so as far as I know all the (user-maintainable) fluids are now synthetic. My son, an auto mechanic himself, says that people like me are called “gravy” to a repair shop.

Why?

What I want to know is what’s next? How can I make it run like it did when new?..

Or at least like it did when it still had less than 125.000 miles on it?

How can I keep this little beasty going?

When new, I was averaging 18.8 mpg… In town! My Highway driving, at 65-70 exceeded 23mpg (22.5-25.4, depending on the terrain). The dealer kept telling me I shouldn’t be getting such good number, even if I was exclusively using premium gasoline. Going up into the Rockies’ foothills with the cruise control on at highway speed wouldn’t even cause the transmission to down-shift in its effort to maintain speed.

Now; however, I’m getting 15.5mpg in town and averaging 19-20mpg on the highway. The tranny kicks down when going up those hills. Don’t like it!

My son and the dealer claim there is no reason for complaint. They also tell me I don’t have to change the injectors because they never wear out. Nor should I have to worry much about the spark plugs. There are cleaners for both. I still change my (synthetic) oil every 3500 miles, the dealer (and my son) tell me it’s excessive to completely drain, flush, and replace the fluid, and replace the filter when doing the transmission service every 30.000 miles… Same with the differential every 90.000… And the fuel filter at the same time. Altough they will happily take my money to do so.

I have started to lose about a pint of oil between changes and my son suggests that instead of replacing the two leaky gaskets (one of the valve covers and the rear main seal), I should wait until it gets real bad and then install a factory-rebuilt into it.

Thoughts? Advice? Anything?


#2

Well…where do I start.

First off…running on Hi-test will NOT increase gas mileage. It may prevent a vehicle from getting worse gas mileage…if-and-only-if that vehicle was meant to run on hi-test. But if the vehicle is designed to run on regular…then running on hi-test won’t help one bit. And since you drive in the Rockies…a car needs even lower octane at higher elevations.

Second…Who says you don’t have to worry about spark-plugs?? Why would ANY competent mechanic say that?? Is this a Diesel???

Fuel-Filter at 90k miles…What does the owners manual say?? That seems like an awfully long time.

Injectors do break…and they also get clogged if abused (i.e. Not changing gas filter often enough).

Thoughts - find a different mechanic.


#3

I have thought of switching mechanics. And have done so. Several times. They pretty much all say the same things down here. They all tell me I should be happy with the mileage I am currently getting, as it shouldn’t have been as high as it was anyway. Why would they tell me that? What is wrong with having machinery operating at high performance, high reliablity, and optimum levels of efficiency? Especially, if it’s as necessary an item as an automobile is in our society.

The owner’s manual recommends 91 octane. The dealer’s mechanics claim I should only need ‘regular’, but its octane rating is 85. My son is of the same opinion, unless it ‘knocks’, then only go up to whatever doesn’t ‘knock’. The hills make it knock, and it drops the above-listed mpg by about 5.

The fuel filter is in the top of the gas tank, and the manual suggests changing it every 100K. Probably due to its location.

The dealer almost always suggests cleaning the ‘O2 Sensor’ and ‘Throttle-body’ due to being dirty, even though scheduled maintenance suggests 60K.

This silly car just got its 4th set of tires at about 225K; I have them balanced during the tire rotation procedure every 5K miles. And even though I try to have an alignment done every other tire rotation, when they go through the procedure, they never have to make an adjustment. Why? My son tells me there is nothing to adjust. If so, this is the first car I’ve owned that never needs an alignment.

I came from old school auto maint; 10W-30 oil change every 3K up in N-E PA (Pocono Mtns). Now down here in Texas; they are telling me with 5W-30 Dino-Oil change every 3K-5K miles, or with Syn-Oil change every 6K-15K miles. It’s kind of confusing to a non-mechanical individual. Give me electrons and magnets any day. Electronics… So much easier!

Way-Back-When, I was told Fuel injectors needed to be inspected for possible replacement every 30K-50K miles, and should be kept clean in-between inspections. Corrosion control kind of thing. Just like Spark plugs; Back-Then - every 15K miles Pull and Inspect the plugs, and then Clean or Replace (I&C/R); Now - 100K miles between any I&C/R maintenance. I know they are not making them any better because they cost about the same now as then (or seem to).

Thanks for your response.


#4

Three choices. Miller Lite, sherry or champagne. These are the only things in my imaginary storage rack. Definitely champagne this time. Of course, this doesn’t address any of your questions but if there is no 235,000 mile celebration, when will it be?


#5

Well, being a computer-math kinda geek, I originally set 250K (256K) miles as my goal in using this car; but when I hit 128K in just over three years, I thought "Hell, I can easily hit 512K miles with this thing. There will celebration when I hit that mile mark. A big one!
But around that point in time (125K miles) I had just started going to a different auto mechanic, too. Coincidentally, it was also around the same time my car started running less efficiently, i.e. lower mpg, down-shifting on the hills, hitting the gas pedal harder to get the same results, and so on. He lasted about 30K-40K miles, and went to a different one. The only thing I CAN’T get a mechanic to check out is the fuel injectors. They all keep telling me they can run cleaner ($29.95) in the the fuel tank and things will be as good as new.
This last set of spark plugs (3rd set at 205K) only cost $2.80 each through the auto dealer. That was supposed to get me my better mpg. Huh?
I had one mechanic that told me to just put in an inline fuel filter when this current in-tank fuel filter goes bad. A Jeep Dealer’s Maintenance Agent told I only needed to relplace the fuel filter when the fuel pump goes bad since they are both inside the fuel tank anyway. Why not suggest I replace them both every 100K miles when the filter should be replaced?
I plan to contact Chrysler when the Jeep hits 500K and ask them what they did right when they assembled my Jeep.


#6

I agree with all of Mike’s points. I’ll add a few.

A pint of oil between oil changes, even 3500 mile oil changes, for a 4.7L with 235,000 miles is EXCELLENT. You may have seepage past a tired ol’ gasket and a tired ol’ seal, but you do not have a real problem there.

Have you checked the recommended maintenance schedule that came withe the vehicle? That’ll tell you when your spark plugs are due to be replaced. If they haven’t been replaced yet and you can document it, I suggest you donate the old ones to Ripley’s believe It Or Not. 235,000 miles on a set of plugs HAS to be a record. An arc of 40,000 vols or so flashes across two electrodes thousands of times a minute. Every time it dooes, a small amount of electrode material is vaporized by the arc. Do the math. Yours have flashed millions of times. The wires that carried those voltage s[pikes (if you have a distributor based system) are probably pretty tired too.

Your mileage isn’t really that bad for that vehicle at that age. But I’ll bet a tuneup would help it be even better.

Lastly, do a compression test. My bet is that the engine’s getting tired (as in tired compression rings and worn cylinders)


#7

Two-fifty is good. Five-twelve can be done and I hope you get there.


#8

Thank you, MountainBike. In this last month, I have noticed a drip spot just starting on my driveway, so I’ll have start arguing with my mechanics so they can start thinking about how to eliminate the leak. There hasn’t been a blue cloud following me, so I don’t think I’m burning oil.

I do try to follow those recommended Preventive Maintenance (PM) guidelines, which my son says the dealer’s mechanics told him I was a ‘Gravy customer’.

I’ve done the Tune-up thing but there was no change in my current mileage readings. The thing that got me was the rather sudden drop in MPG somwewhere between 125K-130K miles. And everything I/we’ve tried has done nothing to bring back the higher MPG.

That’s why I always ask the mechanics about physically checking the injectors.

They are the only items in the fuel system that has not been changed, let alone looked at, all they want to do is run a cleaner through the fuel line. Why is that?

If I’m willing to spend the money, why aren’t they willing to do the work?

Are fuel injectors so infallible? That they never go bad?

I spent my working life in Communication Systems and Computers. I completely understand the need for PM schedules and Corrosion Control. Systems Analysis procedures recommend looking at and corrective actions taken, if needed, on every part or sub-system, in order to maintain the highest reliability of the total system (my car). Sorry, went techy there for a moment.

Have a great day!


#9

Celebrate at 384. Nice round number. :slight_smile:

(the computer nerds will get it, maybe some others)


#10

If the Jeep hasn’t had a basic tune up in the last 50,000-100,000 miles, it’s overdue. (spark plugs, air filter–ignition wires if it has them) If the plugs have never been changed, it’s entirely possible that that’s all that needs to be done to restore the car to perfect running condition.

Using a pint of oil between oil changes is nothing to worry about. There are people with new Volkswagens and Audis on this forum that would be delighted to have your level of oil consumption. If you switched brands of oil recently, try a different brand. Different formulations seem to agree better with different engine designs. If you like synthetic, I’m a fan of Mobil-1 or Valvoline’s ‘Synpower’ personally.

An often overlooked area when it comes to fuel mileage is the tires. If you just got a set of tires and the mileage dropped after that, it could be that the newer tires have a higher rolling resistance than the old ones–it may be a tradeoff of grip, ride, etc. for some drop in economy. First make sure they are not underinflated. Just a couple of pounds of underinflation will make a noticeable drop in fuel economy.

If your Jeep idles smooth, accelerates strong without hesitation, there is likely nothing wrong with the injectors. But at over 200K, one or more of them could be leaking or dirty enough that the spray pattern is not so good. In this case it may warrant replacing, or just running a decent fuel injector cleaner (not the cheapest stuff you can find) for a few tankfuls of gas may help clear it up.

If you like the Jeep, I’d consider getting the valve cover gasket replaced. The rear main seal could probably wait unless it’s really making a mess or oil is burning on the exhaust and causing fumes or a potential fire hazard. There are products that can temporarily swell an ailing seal if it isn’t too bad. You may have some temporary relief with one of these. Typically a RM seal only leaks while the engine is running. If you get the tranny fluid done, I’d only do the fluid and filter, and stay away from the flush.

People are pretty down on these vehicles, and certainly some have issues, but yours is a testament to how well a vehicle will hold up with regular maintenance. And I’ve always liked Jeeps anyway.


#11

I think your son the auto mechanic is way off base on a number of maintenance points from spark plugs to transmission fluid services to fuel filters along with a number of other issues.