Since C4 production stopped in 1996, any
purchase made will be of a used automobile whose condition should always be assumed to be
Because of the mystique of the CorvetteŠ
in general and the drop dead good looks of the C4 in particular, it is
easy to get caught up in the moment and find yourself the owner of a fiberglass basket
Although it isn't possible to list everything you should
check there are some general guidelines that you should follow whenever you plan on
purchasing one of these wonderful automobiles.
The very best defense against buying a carload of trouble is
to ask for the service records. If the automobile has had only one
or two owners, you may be able to get the entire history in this manner however, even if
there has been a whole host of owners, the last owner should have kept the receipts from
the present service history and if he or she cannot or will not produce them, it is a red
All GM dealers conduct their business via computers and if
you approach a dealer to do a pre-purchase inspection of the automobile, you may be able
to persuade them to print out any records related to the VIN number. Although these
records are purged from time to time, it is worth asking.
Finally, if the selling individual will disclose the shop or dealer which
has been maintaining the automobile while they have owned it, you can
approach them with your questions should the seller be unable or unwilling to produce records or receipts
which clearly identify the automobile in question.
If there are no records and no leads on who has been
maintaining the automobile, you will either have to thoroughly check everything on the
vehicle or walk away from the potential purchase.
Often, since the seller will seldom pick up any costs
associated with a pre-purchase inspection, walking away may be
the best idea in these cases.
Still, lets be optimistic and assume you have found what
appears to be a low to moderate mileage C4 that appears to be in good shape.
What to look for in that situation is the question.
Every dealer, every person selling an automobile, everyone
who hasn't spent the last 100 years off the planet knows it is the appearance of an
automobile that first gets a potential buyer's attention and if the visual pleasure is
great enough, the buyer can be rendered unconscious to the defects present in the
This is particularly true in the case of the Corvette.
What to look for
Normally, a savvy seller will have the automobile "detailed"
prior to placing it on the market.
A detail shop will steam clean the engine compartment,
apply a top coat of Armor AllŽ or another of the wax based interior products to the dash,
seats (if leather or vinyl) and all plastic trim.
The shop will thoroughly wash and wax the exterior
with a high gloss wax and apply Armor All to the tires.
Recently, Blue CoralŽ and Dupli-ColorŽ have teamed up to
produce Dupli-Color Color Wax which hides swirl marks and minor scratches in the finish
and detailers are using that product as well to make the appearance as pleasing as
A prospective buyer should look at the exterior
finish in bright sunlight. Although the vehicle has been detailed, you will
be able to pick up subtle clues that there are scratches and paint problems hidden under
the wax if you examine the surface carefully.
Another trick is to apply Armor All to the actual paint. This technique
hides problems with chipped clear coat and will make the front of the C4 in
particular---where stone chips take a heavy toll---look better than it actually
You will also want to look carefully at all the weather strip
material on the car. It is almost a certainty that some of it will be cracked but if
all the strips are in bad shape, it will cost you several hundred dollars to replace
everything even if you do the work yourself.
Inside the automobile
Look for areas of wear in the
A common trick is to apply flat finish matching paint (particularly
if the carpet is black) to areas where the carpet has been been worn through to the car's
body. Unless you look closely, you will think the carpet is in great shape until you
purchase the vehicle and later notice you were tricked.
By the same token, if you observe new floor mats, be sure to
look under them for signs of wear.
In the rear cargo compartment, look for cracked
or damaged trim, broken or damaged top hold down hardware and scratched or otherwise
damaged plastic seat backs.
Finding these situations and pointing them out to the seller along
with protestations that you will have to have the car restored will sometimes result in a lower price.
Many Corvettes have some damage history. Most is very
minor but occasionally you run into some major problems usually caused by an accident.
Before you spend your money, take the time to make sure you are not buying something
that until recently was in a body shop or worse a junk yard.
Unless a fiberglass panel has been actually replaced, it is
relatively easy to determine if repairs have been made.
On the side of the panel away from the side normally
viewed, look for a built up area where the resin and fiber have
been applied to repair the damage.
Look at the underside of fenders, the inside of doors and
inside the engine compartment.
In the rear, take off the license plate and using a mirror
and a flashlight, look at the rear of the automobile for damage.
When a fiberglass repair is made, the area is
reinforced with fiberglass material and often stiffeners or doublers are installed to make
the repaired area strong. You should never see bulges or areas where the
underside of the fiberglass is raged appearing and thicker than normal unless a repair has
Symmetrical built up areas are acceptable if they are
obviously part of the fiberglass structure formed when it was originally laid up.
These areas will be smooth and very commercial in appearance. There will be nothing
ragged about them nor will they appear to have occurred recently.
Frame repairs normally show heat discoloration or slight
wrinkles where the metal has been reformed.
While the car is on a lift, look closely at all of the frame
structure and supports for any sign of heat treatment or wrinkling.
While you might tolerate a little fiberglass repair
you should never buy a Corvette that shows frame damage. Unless the repair is perfect, uneven tire wear, poor
cornering, pulling to one side and even life threatening situations are all
possibilities. It isn't worth it.
You will want to climb into the cockpit and take the
automobile for a spin right away but wait a bit on that. If there are serious
problems present, why bother?
First go to where the car is located, do not allow
the car to be brought to you. The reason: you want to see how
the engine starts when it is cold.
After you have performed the visual checks of the appearance
items, you will want to take a look at a few areas. Here are some things to check:
- Check the tires for remaining tread and any signs of sidewall
damage or plugs and for any uneven wear..
- Note how easy the clamshell hood is to operate. It
should release and lift without binding.
- Feel the engine's valve covers to make sure the engine really is cold.
- Look for any missing fasteners or loose cables anywhere in
the engine compartment.
- Look closely for any signs of oil leakage. Take a
mirror and check the rear of the intake manifold as this is an occasional source of leaks but
difficult to see from above.
- Inspect the plug wires for signs of cracking or damage.
- Look at all the many hoses for cracking or leakage.
- Look at the serpentine belt for signs of fraying.
- Check the battery terminals for corrosion.
- Remove the air filter cover and check the air filter
- Check the entire front end again for signs of physical damage
- Check the coolant tank to see that it has sufficient coolant
according to the marking.
- Pull the dipstick and check the oil. If it has had a
brand new oil change, be especially vigilant.
Also, be careful if the oil viscosity feels "stiff". It is a common
practice to put oil additives in the crankcase to hide excessive oil usage.
- Press the hatch release on the edge of the driver's door and
the hatch should release on a hatchback model. Reseat the hatch and perform the same
test using the yellow button in the glove box. If you hear a solenoid sound but the
hatch does not release, there may be misalignment of the retainer. No activity
indicates a blown fuse of bad release solenoid.
- Check the security system. Lower the power windows,
exit the car locking them with the power locking switch as you do so. With the door
lock key at the ready, reach into the vehicle and open the door. The alarm should
sound (horn should pulse) and this will continue until you unlock the door using the key.
Replace the air filter cover and ask the owner/dealer to
start the engine while you watch.
- Note if the engine starts immediately (Within 2-3 seconds of
cranking when cold).
- There should be no "knocking" sound for more than a
second after start up.
- Note if the owner/dealer depresses the accelerator at all
(Look at the throttle body where the throttle cable attaches to it for any sign of
movement when the starter is engaged).
If the engine is slow to start or the owner/dealer
"helps" it, there may be hidden engine problems. A knocking sound that continues
for more than just a second indicates rod bearing/lower end problems and is potentially
very serious and expensive to repair.
When the engine starts, ask the owner/dealer to immediately
turn it off and reposition yourself to the rear of the vehicle. Wait one minute and
then ask the owner/dealer to restart the engine while you watch for any sign of smoke from
the exhaust. (If it is a cool or cold day, do not confuse condensation with oil
smoke. Condensation will be odorless, oil smoke will not).
Oil smoke normally indicates problems with either
the piston rings, the valve guides or both.
Allow the engine to idle for a full three minutes after
which time it should be running smoothly unless the ambient temperature is very cold in
which case you may have to wait as long as five to seven minutes.
When the engine has warmed up, pull the PCV valve (the hose on the left
side of the engine going into the valve cover) and make sure very little oil
smoke comes out the hole where the PCV valve formerly was located. A very
small amount is OK but none if what you want and any more than a tiny amount
indicates cylinder/valve guide problems.
After the engine idle is as smooth as you feel it will get, place
your hand near one of the two exhaust pipe outlets and feel for a smooth,
almost continuous pressure. You are doing an elementary test for a weak
cylinder. and if you can detect instances where the pressure varies
here, there is at least one cylinder with very low compression indeed.
Again ask the owner/dealer to shut off the engine and then
immediately restart it.
It should start immediately and there should be no
sign of oil smoke at the instant it "catches" or again, there may be piston
ring/valve guide problems present.
Additional Mechanical Issues
Leaving the engine run, exchange places with the
owner/dealer and perform the following checks from the cockpit:
NOTE: All references to the LCD, Digital Dash
or Electronic Instrument Panel, apply only to the 1984-1989 models of the C4
Corvette. 1990 and later have a traditional instrument gauges plus a LCD
- Check the power windows, power door locks, power seats (if
present) and power rear view mirrors for proper operation.
- Examine the Electronic Instrument Panel. The LCD
display should have the same amount of light present all across the display. (i.e.
no part of the display is darker than any other). If not the case, one or more of
the four very expensive bulbs in the instrument panel have burned out. With the
labor involved, replacing even one bulb is $100 minimum and all four will cost over
twice that amount).
- Observe that there is a trip odometer mileage reading,
remaining range and average MPG reading available for display on the Electronic Instrument
Display. If not, there are problems with the unit and a potential repair bill of
several hundred dollars. (You must verify this later to be certain as will be
- Turn on the parking lights as and operate the headlamp
switch. Check that both headlights rotate to the up position. Leave the lights
on for now.
- Block the photocell on the digital dash (it's the small,
clear window above the speedometer at about 11 o'clock) and rotate the dimmer knob on the
headlamp switch. The instrument panel should dim. If not, that's another big
repair bill to make it work.
- Exit the vehicle and have the owner/dealer operate the
bright/dim headlamp control as well as the turn signals. Do all the external lamps
work (including the cornering lights when the turn signal lights are flashing)?
- Return to the vehicle and turn on the air conditioner and
radio. Place the headlamps on high beam. Switch the coolant temp/volts switch to
volts and observe the reading. A reading of less than 11.5 volts with this load
indicates potential alternator/battery problems.
- Turn off headlamps and parking lamps. Adjust the air
conditioner and verify that it produces cold air. If the controller is the
electronic variety, set the temperature to the lowest setting (press the cool button until
the display will not indicate any lower) and observe that the A/C fan goes into it's
highest setting. Then press the warm button until the fan speed drops back.
Observe the indicated reference temperature and determine if you agree that the setting
approximately matches the actual ambient temperature in the vehicle. If so, the
controller and A/C appear to be OK.
- Turn the radio off. Check that the antenna
retracts. Turn it back on and verify the antenna fully extends and that the radio
works on both the AM and FM band plus make certain that all speakers work. You
should be able to place the volume control to 1/2 to 3/4 fully clockwise and the speakers
should not distort the sound.
- The engine should be at or near operating
temperature: Check the idle oil pressure and temperature plus the coolant
temperature. (If they are not at operating temperature yet, check them later but do
make sure the sensors are giving you an output. Note that you will get a red warning
light if the oil pressure is low. It should never be low except at the instant of
startup and then only for a second or so).
- Exit the vehicle and (if an automatic) pull the transmission
dip stick. Make certain the transmission fluid is at a proper level. If the
car is a manual transmission, have the owner/dealer slowly
clutch while you listen for any chattering sound or observe any tendency for the car to
lurch as the clutch is slowly engaged which may indicate a slipping clutch.
Obey all traffic laws and do not endanger yourself,
anyone else or any property as you perform the following tests:
- Return to the drivers seat and fasten the seat belt.
Make sure your passenger does the same. Note that there was a service bulletin on the seat
belts for the slackeners. If the owner/dealer doesn't know if the SB was done, a
Chevrolet dealer should be able to find out from the VIN number. In any event,
make sure you can obtain slack on both shoulder belts.
- With your foot securely on the brake, place the transmission
in a forward gear. If a manual transmission, slowly engage the clutch and observe
for a "chattering" feeling. If automatic, observe for delayed response to
being placed in gear or unusual noises as the transmission engages.
- Check the transmission in reverse for the same symptoms.
- Drive the vehicle and observe for unusual sounds or lack of
response. (You will hear the ABS system cycle and see a yellow caution light flash
on 1987 and later models when you first move the car. This is the normal testing of
the system by one of the computers. If you don't see this happen on 1987 and later
models, there is something wrong with the ABS system).
- Look for erratic shifting in an automatic transmission by
trying different acceleration regimes. The shifts should be swift and sure no matter
what the load on the transmission (meaning no matter if you "get on it" or
"baby it", the transmission should perform properly.
- Look for synchronizer problems in a manual
transmission. The shift points should go smoothly with no need to "double
clutch" or "coach" the transmission into changing gears. There should
be no problems with either up shifting or downshifting and the shifter throws should be
short and positive.
- On a flat road, check that the vehicle rolls straight and
true without pulling to either side. (Note that the road must not have a "crown"
and must be flat in all other respects or this test cannot be conducted).
- In an area where it is safe to do so and the road is flat,
accelerate to 30 MPH and apply the brakes as in a panic stop. The car should stop straight
ahead without pulling to one side.
- Accelerate again to approximately 25 MPH and make a gentle
stop listening for the shrill sound that indicates that the wear limits on the brake pads
has been exceeded.
- In an area where it is safe to perform the test, accelerate
to 20-25 MPH and rapidly move the steering wheel to the right and left approximately 15
degrees. The car should respond instantly and there should be no "slop" in
the steering linkage. (When you move the wheel even a tiny bit, the car should respond).
- In an area where it is safe to do so, accelerate to 40
MPH and move the steering wheel approximately 30 degrees first to the right and then to
the left. There should be no sway at all. The car should track as if it were
on rails. you should hear no snapping noises or other unusual sounds. Suspect
suspension problems if the car sways or if you hear unusual noises.
- In an area where it is safe to do so and while traveling at
30 MPH or greater, engage the cruise control by momentarily pressing the "set"
button on the top of the turn signal control. The computer should capture and
maintain the speed you are traveling at the moment of engaging the system. Press the
set switch again for an instant and the speed should increase one (1) MPH. Press the
coast button for an instant (it is located at the end of the turn signal arm) and the
speed should decrease precisely one (1) MPH. If the system works in this manner, it
is working properly.
- Press the clear buttons on the trip odometer and average
mileage (MPG) displays and observe that new calculations begin. To verify that this
system is working properly, when you next shut down the engine, make a note of the
readings. If they have disappeared when you then restart the car, the Electronic
Instrument Panel definitely has problems and the repair will be expensive.
Drive the vehicle to a service station with a lift and once
the car is elevated on the lift, inspect the underside as follows:
- Inspect the underside for any signs of engine oil or
transmission fluid leakage. Even a drop is cause for alarm depending on where it is
coming from. Check the rear axle for the same thing.
- Inspect the suspension for broken or damaged
components. (Also inspect the shock absorbers for any sign of oil leakage.
They should not have oil present on their exterior).
- Inspect the exhaust system for any signs of damage, broken or
loose hangers or corrosion. Look carefully at the exhaust manifolds for any signs of
cracking or damage as well as the pipes, cat converter and mufflers. These are all
expensive items to replace.
- On a high mileage car, look carefully for any signs of rust
or corrosion on the frame or supporting structure.
- Again search for any sign of collision damage, looking at the
frame in particular for any signs of straightening or heating.
- Examine the steering arm rubber boots for signs of damage.
- Check the spare tire and jack.
- Examine the tires for signs of uneven wear which would
indicate alignment problems.
- Finally, lower the car from the lift and using the procedures
explained in the ECM/PCM codes section of this web site, determine if any
trouble codes are present in the ECM/PCM's memory.
If the vehicle passes these checks, depending on age you may
wish to have a cylinder compression test performed. If you are suspicious by nature,
you may also wish to make sure that the serial numbers match and that the car has not been
modified for speed contests in any manner. These checks are best made by a
professional repair shop or GM dealer.
A car that passes the tests above would appear
to be in reasonable mechanical condition but the one thing you always have to remember is
the car is perfect, why is the owner getting rid of it or why did the previous owner trade
it in to the dealer?"
In other words, you can almost certainly expect to
spend money on a used car when you purchase it!