Look for rust around the tire wells, and on the ZX series, especially across the front edge of the hood. Also check inside the rear hatch for rust bubbles on the surfaces there. These cars are not super- rusty, but they don't resist salty conditions as well as some others. One more problem/giveaway area is the seams on the rocker panels under the doors...look for rust bubbles under the paint.
Crouch down and look down each side of the car in good light. Look for ripples and waves. These indicate old body work, which may be a no-no. (You can't tell how deep bondo is from tapping on a fender.)
A good ZX should start with no more than 3-4 seconds cranking. (Mine can sit for two weeks and starts with less than one second cranking...)
I also recommend a wet & dry compression test by you, or by an independent mechanic shop. This is very easy and cheap - one just removes the spark plugs, screws in a pressure gauge, spins the engine a few times, and notes the pressure achieved. This is done on all cylinders (with the same number of engine rotationss on each, to keep pressure readings relevant), then than you back, and squirt some oil in each cylinder and do it again.
If the dry compression is UNDER 130 psi, the engine is showing some wear. If there is more than about a 15-pound difference from high to low (maybe 140 high, 125 low) than you have one cylinder which is significantly weaker than the others. Not real good news. You can expect the "wet test" (with oil) to be a bit higher, as the oil falls on the piston rings and seals them. If the pressure comes up a LOT on the wet test, like 20+ psi, you have bad rings! If the dry pressure is too low but the wet pressure does NOT come up much, that means the problem is valves, as they don't benefit from the oil squirted in.
If the pressure is a bit low but even across all cylinders (perhaps 115 all across) the engine is worn, but at least it's even. The car will drive OK since the cylinder performance will be balanced, but the car will lack power and needs to be rebuilt when the wear gets a bit worse.
Most Z's have good engines if they have good power. The straight-6 engine is one of the finest and longest-lived ever built! Even if pressure is a bit low, if you care for the engine carefully, you could have a long reprieve before a rebuild is necesary.
Check all the gauges and accessories to make sure they work. If someone has installed an aftermarket stereo, for heaven's sake take a look at the wiring and see if it's a nightmare!! Not much you can do about it, but it makes an arguing point and you know you will have to get it straightened out. Allow at least two hours' labor for fixing it, or deduct $100-$150 in purchase price.
Dash cracks across the top of the dash are normal in old Z's. It has to do with the type of vinyl used by the manufacturer. If they really offend you, you can get a dash cap or a carpet cover for the dash for about $80. Replacement dashes start about $200 for used ones, and new ones from the dealer are $700 plus. (Live with the cracks or add a cap...)
If the rear hatch carpet is toasted by the sun, don't worry - for under $100 you can have a car interior/upholstery shop make a replacement.
A cold Z should have at least 60 psi oil pressure at road speed (3000 rpm). When it's warm and at idle, it's OK for the gauge to drop low - even down to 10 or 15 psi. This is how Z engines work. If it does NOT top 50 psi when fully cold, I would worry about it. That's too low for this engine. It's worn.
The front ends are pretty stout on these. But have the shop check the brakes and look for bent wheels, as replacement wheels are pricey unless you get lucky at a wrecking yard.
If the car is a turbo, think carefully. Most people don't have a clue about how to take care of turbos. The boost gauge should hit the red line within one second if you are at 3000 rpm or above when you floor it. If you don't see that gauge hit at least the lower end of the red zone, the turbo is dying. NOW - you can get a rebuilt turbo for $500, and it takes a minimum 6-8 hours' labor to install it. This may not be prohibitive if you really want a turbo. Just budget accordingly. IF you replace a turbo, replace the oil feed line which goes to it. This adds at least one hour labor but is the best insurance you can have. They do get plugged! (Then NEVER use anything but synthetic oil in it!!!)
I do not recommend automatics in Z-cars. (As a friend says, the "Why?" question comes to mind....). If you want a real sports car, get a sports car - which means a 4-speed or 5-speed stick. (Automatics reduce the performance, too.) The transmission should not grind on shifts or pop out of gear when decelerating, and the rear end should feel tight. If you feel "slack" in the drivetrain, have the shop look at the rear motor mount and look at the rear end. Used transmissions are widely available, but changing one is a day's work.
Do NOT buy the car without talking to the past owner, if it is humanly possible. When I buy used from a dealership, I try everything in my power to talk to the past owner. I want to know WHY they're selling. (In my case, they had ONE kid and decided they hadda have a Suburban. Please, my brain reels.........)
EXTENDING ENGINE AND DRIVETRAIN LIFE:
I am absolutely adamant about the virtues of running synthetic lubricants in performance cars. That means engine oil like Mobil 1, Amsoil or RedLine. These makers' synthetic lubes are also highly recommended for transmission and rear end. They will smooth the shifting and extend the service life of lubricated components. If the past owner used them, you can bet that owner took much better care of the vehicle than usual!
I'm on my 4th Z and never wore one out...just sold 'em and got another. Now driving a 1983 ZXT.
Al Powell, Ph.D. 107 Reed McDonald Bldg. Texas A&M University College Station, TX 77843 Http://agcomwww.tamu.edu/agcom/satellit/alpage.htm