When to do tune-up?

[KU40]

My Explorer has 172k on it, I bought it with 150k. It runs fine, only has a slight engine vibration/warble when idling. I don't have any idea what kind of maintenance the previous owners did on it. It seems well maintained, though, because of how well it runs, looks, and feels.

Should I just take a spark plug out and see how it looks? I forget if these need specifically torqued when put back in though? Or are there any other tipoffs to when it may need it?

I get 17-18 mpg on the 70 mph highway, 19-21 on the 55 mph highway I take to work (in the summer, it's down around 17 now in the winter). The EPA estimates 19 on the highway. I just kinda figured I'd get quite a bit better mileage on my trip to work since I drive at the supposedly great mileage speed of 55.

[dkjones96]

I'd have recommended you did a tune-up when you got the car. I did one Sunday on the Durango and I'd gotten it the day before. Mostly as an exploratory mission.

The plugs being pulled tells you how the engine is running, getting it up on a lift(or getting under it) tells you if people decided to go off-roading in it and messed up or any collision damage that might not be on the carfax, changing all of the oils tells you a lot too. In my car they'd changed every oil in the thing and it barely had 40k miles on it when I got it Saturday. Diff oils, transmission, t-case, and coolant had all been changed.

Granted, that should probably have been checked before the car was purchased but with me it was a major rush to get into a vehicle.

As for your plugs specifically, I've worked on a couple of those explorers and if you are going through the hassle of taking one of the plugs out you might as well do them all. Plus, one plug won't tell you the whole story, you want to pull all of them so you know if one injector isn't firing right or something.

[KU40]

I've been under my Explorer numerous times, as I've done all the previous oil changes as well as changed out the shocks and muffler. It all seems pretty good and surprisingly clean. Though it was nearly out of rear differential oil when I bought it. Unfortunately didn't find that out until a couple of weeks later . But surprisingly there doesn't seem to have been any obvious damage from it, as that was nearly two years ago.

I also forgot to mention that I only get about 13-14 mpg around town, and the EPA estimate is 15. I just figured with the way I drive (conservatively and mileage-conscious) I'd be getting a little better.

I see you have a Durango, do you know much about them (historically)? I only ask because my mom's Durango, I forget the year but it's late 90's, has suddenly decided to plummet the mpg. She claims to now only get 7 mpg and really not much better even on the highway. Do you have any idea what could cause this? My stepdad is pretty big on maintenance so I think it has been handled all right in that regard.

[VetteOwner]

umm have u checked the rear differential since? that oil should not go anywhere unless theres a leak(either from the pumpkin or out the axle shafts into the brake drum)

also grease/check the u joints on the differential, those can cause vibrations.

repack wheel bearings, check brake pads, check fluid levels, change fuel filter, change pcv valve/breather filter, check to see if all the lights work

regarding your moms durango i know on other cars if the O2 sensors take a dump usually cause low mpg yet still runs fine(goes into some factory default thing thats typically rich) that and its a dodge

[dkjones96]

So far I think I'm averaging about 2-4 mpg above the all city rating of 11.

The O2 sensor can't be completely dead because OBD2 would complain but it could be reacting slowly causing worse mileage. Was it a sudden drop in mileage? Maybe the switch to winter blend? We have that here tho...

I agree with VetteOwner, check for leaks in that diff.

[theholycow]

A few ideas...some of which may or may not apply to your Explorer or your mom's Durango:

O2 sensor failure would probably throw a code. If the O2 sensor is providing a believable (but wrong) signal, I imagine it could make FE plummet without throwing a code.

Tire pressure, or changing to different tires, could cause FE to dive and the driver may not give it a second thought.

A locking torque converter that lost its ability to lock might not throw a code.

An automatic transmission missing its first or fourth gear can conceivably go unnoticed. Maybe even third...but I don't think missing 3rd on those vehicles would cause a large FE hit.

A failing belt-driven accessory (alternator, steering pump, etc) could work but drag a lot, I guess.

Deferred maintenance, as you suggested, could cause it, especially if there's lots of stuff that wasn't done. Spark plugs, wires, fluids, air filter, etc. Edit: Also EGR, PCV, that kind of stuff.

Dragging brakes could manifest as a FE drop without other symptoms.

Wheel bearings on modern vehicles can fail with seemingly no symptoms, or any of a million normal or intermittent symptoms. I've been through a lot of wheel bearings (it's my weakness; I beat the hell out of them, I refuse to slow down for bumps, off-roading, or curbs). If all four wheel bearings have failed silently, they could cause a lot of resistance, and maybe only do so once heated up. Here's a few tests:
- Classic tests: Raise the vehicle, grab the top and bottom of the tire, and try to wiggle it by alternating pushing/pulling the top and bottom.
- Drive and listen for what sounds like aggressive tire noise.
- Raise the vehicle and see if the wheel spins freely. This one may need to be done immediately after an extended highway-speed drive to heat up the failed bearing.

Winter can drop FE significantly due to winter blend gas, extra idling, cold air, increased electric usage, and other things.

[dkjones96]

I could see a missing first gear going unnoticed.

Checking tire pressure would be another good idea. The tires in my car were 20psi low when I got it. You couldn't really tell except that the ride was softer than it should have been. Even that low the side walls didn't really look to be buldging much more than usual inless it was parked unevenly.

[KU40]

Thanks for the replies. Lots of things to think about/look into. Don't worry, yes I've checked the differential oil level since then. About......80 times . I was pretty nervous about it so I got OCD on checking it. It hasn't gone down at all since. So I don't know if somebody did some work back there and just forgot to put oil back in or what. Strange.

I've done the push/pull and up/down tests on my wheels before, as I had a noise in the front end when I went over bumps when I first got it. My stepdad was all worried about the wheel bearings because he had just changed them in his sister's F150, but mine checked out fine. The shop recommended changing upper ball joints, so we did, and clunk was still there. Finally a year later a mechanic got smart and found out it was just sway bar bushings on the frame (I wondered if it wasn't just this the whole time, but there was beginning to be a little play in the wheel so ball joints needed changed anyways). Wish they would have found that $60 fix before the $500 ball joint suggestion. But oh well.

I thought about the O2 sensors on the Durango and told my mom to think about those. and yeah, Dodge wouldn't be my first choice either, but my stepdad loves them. So what can you do.

[shatto]

The original question asked about a tune-up.

Modern engines, and vehicles, have nothing to tune up.

There are replacement items; brake pads, fluids, timing belts, wiper blades.

Here are some things you ought to do:
*replace brake fluid about once a year. Sooner if you are in a humid or wet climate.
*replace differential oil at the 50,000 mile range.
*replace the power steering fluid then too.
*change transmission fluid at the proper time.
*change anti-freeze...'coolant' to you youngsters, yearly. Distilled water only.
*change your 100,000 mile sparkplugs on time. Might add upgraded wires then, if you've got em.
*rotate the tires every 5-10,000 miles.
*buy a liftime alignment and have the alignment done at 10-20,000 miles
*check serpantine belt idler and tensioners which can get out of alignment and you'll think the belt is bad.

You may, but don't need to, replace hoses and serpantine belts.

Never use Stop Leak except to get home from the middle of the Mojave Desert, as it just plugs the heater core and radiator.

You do not need additives of any kind, anywhere; if you use a top of the line lubricant such as those from Amsoil.

[VetteOwner]

lol tons of stuff on modern vehicles to tune up, just as same as before! cars havent changed much at all since 1909.

definately change plug wires when you change plugs, they wear out faster than good plugs anyways.

brake pads/shoes check them but only repalce when theres less than a 1/8" left, or if they squeak when you press the pedal(that metal tab rubs on the rotor causing a squeak and tellign you to change them)

id leave the brake and power steering fluid alone, its just a big PITA and a waste to be changeing it since thier both closed systems there shouldnt be any contaminants of any kind in them. i only replace them when i have to service either of them where i have to drain the fluid/bleed brakes anyways.

same with antifreeze, it has a 5 year 100,000 gurantee on it and if its not changing colors leave it alone.