I am rebuilding my 2003 4Runner V8 with 222,000 miles and just wanted to know what are some of the most useful preventative maintenance repairs and upgrades available. I want to keep my ride very clean, understated, and as ORM looking as possible.
If the ride is new to you,
check/change all the fluids unless you have receipts for them being changed. Engine Oil, Transmission Fluid, Differential(s), Engine Coolant, Power Steering, and Brakes.
Fumoto Valve on the engine oil pan makes oil changes stupid simple. I don't have to use any tools to change my oil and the ride is high enough that I can just lay under the car and do it. I use full synthetic 5W30 - usually mobil1 or Valvoline from Walmart or Costco. Wouldn't be bad to send off an oil sample for testing to see if there's any cause for concern in your used oil.
Timing belt every 90k. If you've just purchased this and don't have clear evidence of it being replaced. This is the single most important PM you can do. If the belt breaks, you may toast the engine.
Water Pump whenever you do the timing belt, or visa versa.
Radiator hoses - if you change the water pump, you'll have to change coolant. Might as well replace the radiator hoses with new OEM or some fancy silicone. Better "now" than unexpectedly..
Spark Plugs - check them and replace. They're easy to change. Check coil packs for wear and replace as needed.
Brakes - front calipers tend to seize up. Jack up the front and see how easily the front wheels turn. Shouldn't be much resistance. You could barely turn mine when they were seized. You'll get really bad MPG and wear out pads quicker without fixing it.
Power Steering - the reservoir tends to get stained in such a way that it looks full, pop open the cap to make sure the levels are correct. (I've mentioned this twice now for a reason, lol)
Lighting - LED EVERYTHING you can. All of it is way better. This has come so far in the 18 years since your 4Runner was manufactured. Headlights, interior lights, etc. Fogs are a bit difficult to source where they actually function as fog lights and not just "more lights" - Headlight housings fade over time and REALLY date the vehicle. This is a good time to look up the mod to put 06-09 headlight housings on your ride. The projector beams are much better, and LED headlights are very good these days.
Front and rear suspension bits. At this age, a lot of rubber stuff is worn out, and a lot of ball joints are torn/leaking or otherwise damaged. Shocks/struts may be worn out if they're original or just old. If everything is worn, your ride will be soft and uncertain with some loud noises when you hit bumps too quickly.
Driveshaft U-Joints - if they have play in them, you'll have clunks and clanks and vibrations. If you have a 4x4, they'll have zerk fittings to re-grease them. You want to be re-greasing them at least twice a year, minimum.
Seat Foam or Upholstery your drivers seat is probably super flattened by now. New OEM seat foam is a breath of life. It's a few hundred bucks well spent. leatherseats.com has really good reupholster kits in a bunch of colors and options. Can't recommend them enough. Took me about a week in the evenings to do it all myself with zero experience. about 24 working hours and I added heated seats.
New stereo Head Unit / Backup Camera If not equipped, a backup camera and a touchscreen with Android Auto and/or Carplay are the biggest things that outdate these vehicles. I came from a 2015 RAM, 2015 CRV, and 2014 Outback as other family cars, and the biggest difference is the dated-ness of the radio, etc. Once changed, I have no desire for a newer model vehicle, personally.
Headers if (and only if) you have a ticking noise from the exhaust manifold, and it bothers you... Don't get OEM replacements - they'll crack again. You can get Doug Thorley shorty headers and put catalytic converters on them to maintain factory setup with something that'll last. With the factory exhaust still in place, you won't be obnoxious or really much different in noise.
Professional detailing it's always nice to get someone to really spend some time on things like really getting the carpets and corners cleaner than a normal wipe down. Plus, it'll point out areas that "can't" be cleaned - which will help guide you down areas to restore with new parts.
Beyond all this, wheels, tires and suspension are all personal preference. There's hundreds of pages about options in that arena. Be conservative with aftermarket suspensions if you want understated. Don't get caught up in taller and stronger suspensions. I regret not getting adjustable valving shocks/struts in the first place.
