Bonefish wrote:ok, so I got my first care. It's a 94 Lumina, with about 135k miles on it. Paid 650 for it, so I think I got a sweet deal.
Congratulations! If the car runs and drives, and cost $650, it'll be an excellent deal. It may not last forever - read: there will come a point when it's less expensive to buy another car than to fix this one - but, with proper care, can, you know, BE A FUCKING CAR! Very cool.
Bonefish wrote:But, here's the question: what can I do to improve my gas mileage? I put 89 octane in the tank, but I'm not sure if that's actually worth it...
It won't be. If you can afford it, I recommend buying name-brand gas - it's basically guaranteed to be consistent in its quality, while off-brand gas will often change suppliers week to week - but buying higher-octane gas will rarely benefit mileage. [There are sometimes other reasons to get it, but you don't fall into any of those categories.]
I typically run a few tanks of Shell's premium through any new engine I buy, and then continue using Shell; even their lowest-octane gas has cleaners and such, which is a contrast to most companies, who only put the good stuff in their good stuff. But a tank of reliable fuel injector cleaner is a good head-start to cleaning stuff up. Still, one shot won't undo years of shit gas, so good fuel is important on an ongoing basis.
Bonefish wrote:But yeah, what should I do? Replacing the spark plugs seems like a safe bet, but what else?
Well, here's where I caution you. The car you have is renowned for its lack of reliability. It's often called the "Lemina." [Lemon + Lumina.] But that's not necessarily a problem: I drove the car with GM's lowest customer satisfaction rating
ever for 314,000 miles. But yes, it does mean that they have some mechanical problems, and that repairs may be necessary at a higher rate than another vehicle.
Let's put fuel mileage in perspective. Let's say you got the engine that most people got: the 3.1 liter V6, GM's standard V6 powerplant at the time [and a pretty decent engine]. In the Lumina, it could be expected to get something like 20 MPG, driven calmly, with a city-leaning mix of highway and urban driving. Let's say yours is gummed up pretty bad, and only gets about 15. If you drive 15,000 miles a year - about the average for your age group, an average which includes a lot of people who live a
long way from where they work - and pay $4 a gallon for gas, your "bad fuel economy" will cost you $1,000 per
year.
Chances are, your actual economy isn't going to turn out to be that bad, and your mileage probably won't be nearly that high. [Unless you're driving 20 or 30 miles to work each day, and another 20 or 30 back.] Chances are, you'd only get less than $500 a year out of restoring your car to brand-new condition! So don't get carried away with fuel economy: it's easy to spend far more than you're ever going to save. From an economic standpoint - and, hell, an environmental one - concentrate on keeping the car
going. 
For example, replacing spark plugs probably wouldn't offer a positive return-on-investment, unless there's something
wrong with them.
But mileage deserves attention, so I don't want to ignore it, either. So the first step is, what kind of mileage are you getting now? It's not worth a ton of attention if you're only getting 18MPG out of her, but if you're getting 5, there's probably something quite wrong. Get a tank of decent gas, write down your mileage, drive until you're almost empty, fill the tank back up to the same level, and divide the number of miles you drove by the number of gallons you just put in. [Which I'm sure you already knew.]
More generally, which engine
do you have? The 4-cylinder Luminas will have very different issues from the V6.
Does it leak anything? I assume it's an automatic, so how are your levels of transmission fluid and oil? Coolant? When the engine's been running for a while on a hot day, how does it smell?
When the car's not been running for a while, run your finger along the inside of the tailpipe, as if it were Jeff's rectum. Does it leave a thick, resiny soot on your finger, or just a light dusting of dry black powder? Soot in the exhaust often means a sensor is out of whack, and sometimes a $50 sensor can get you 5 MPG in economy. Tracking down
which sensor is out of whack, on the other hand...
This being a Lumina - or, to be honest, any 90s GM - I would assume that a check engine light is on somewhere. [If it isn't, check to make sure the light isn't burned out; it should briefly illuminate when you fire up the car.] GMs at the time had very stringent requirements for being in good working order, and rarely stayed in perfect working order, and thus constantly tripped check engine lights; this often isn't a problem, but you can have it scanned [free] and get a better idea of which sensors might be trouble. And if the light is good, but not on, then you know someone's been taking very nice care of your ride.
So here's what I would do right away:
- A few tanks of good [preferably Shell] gas. Maybe some injector cleaner, particularly if you notice soot in the tailpipe.
- Oil change. Start off clean. Do it yourself, and use Valvoline Max-Life Synthetic, and a brand-name oil filter [Fram's good]. Don't ever put anything but Valvoline Max-Life Synthetic in it ever again; there are other oils I'd recommend if you drove an M3, but for a high-mileage car, this shit's gold. [edit: While you're changing it, look in the discarded oil: is there anything but oil in it? Like antifreeze? Or metal?]
- Check this other stuff everyone's mentioned: your mileage, the condition of your brakes, how sooty your tailpipe is, any weird noises or vibrations, wheel shake at speed, etc. Report back, because we love this stuff.
- but rather downshifted through the gears, bringing me to a halt without ever touching the brakes and raising my fuel mileage upward of 30 MPG with a 25-year-old race-modified car. But the convenience of an auto in the Jeep is really something, and makes left-foot-braking a lot easier than in a manual; another tough decision for whatever '96 I buy.
