A. When engine and radiator are cool, remove pressure cap on coolant fill reservoir located at the right rear of the engine compartment by:

- slowly rotating cap counterclockwise to detent. (Do not press down while rotating)

- wait until any residual pressure (indicated by a hissing sound) is relieved.

- after all hissing ceases, press down on cap while continuing to rotate counterclockwise.

B. Open radiator draincock to drain coolant.

C. Close draincock and add sufficient water to fill system.

D. Run engine, drain and refill the system, as described in steps 1, 2 and 3, a sufficient number of times until the drained liquid is nearly colorless.

E. Allow the system to drain completely and then close radiator draincock tightly.

F. Remove and clean coolant recovery reservoir located at the right front of the engine compartment. Reinstall  reservoir.

G. Add a 50-50 mixture of water and ethylene glycol antifreeze that meets GM specification 1825-M. Fill high  fill reservoir to the base of the filler neck and add sufficient coolant to the recovery reservoir to raise level to  the full "COLD" mark on dipstick. Reinstall recovery reservoir cap.

H. Run engine, with pressure cap removed, until normal operating temperature is reached; radiator upper hose  becomes hot.

I. With engine idling add coolant until level reaches bottom of high fill reservoir filler neck.

J. Do not use pellets in LT5 cooling system.

K. Install pressure cap, making sure arrows line up with the overflow tube.

Oil should be changed at approximately 3,000 miles (for non-synthetic oils) and up to 5,000 miles for synthetic types. However, particular conditions may suggest more frequent intervals. For instance, a stored vehicle which is periodically moved only short distances can allow fuel to pass through the unseated rings contaminating the oil. Check oil for both a fuel smell or for "beading" on the dip stick. 

There are several oil filter brands available and some claim better oil retention in the inverted position reducing the initial tensioner rattle upon start up of some LT5's. This may or may not be true. The recommended AC oil filter is the PF970C. If a tensioner rattle is prominent (first few seconds after start up), there is a corrective tensioner kit (we'll cover that later). The "Oil Change" light is mileage activated. That is, every 7500 miles the light will come on regardless of when the last oil change was performed.

It is a simple reset procedure and is explained in your owner's manual.

Again, these changes are only suggested for severe conditions.  One particular area usually overlooked during routine service intervals is the clutch and brake fluids. The brake master cylinders are located directly in front of the brake booster on the left side of the engine compartment. The clutch master cylinder is located behind the ECM (computer) requiring it's removal for access. Be careful with all hydraulic fluids as they can stain and remove paint even on initial contact. The clutch and brake fluids are originally clear however, after a normal use period they become dark. Both these systems should be flushed and filled with the appropriate fluids at regular intervals depending on the vehicle's use.

First, the Corvette ZR1 has no front grill therefore, it relies heavily on the air deflectors underneath the front bumper to direct airflow through the radiator to dissipate heat. Damaged or missing deflectors will cause overheating. The "bottom feeder" design also works wonderfully as a vacuum cleaner for our roadways, however, the downside of this is that the Corvette's radiator becomes highly susceptible to accumulating debris which will reduce airflow and therefore increase operating temperatures.  Depending on your climate, the ZR1's cooling system requires regular maintenance.

Once a year the system should be drained (best done by loosening the lower radiator hose) and refilled with an approved coolant. We also highly suggest using distilled water because the aluminum alloys present in the LT5 and radiator actively promote the formation of scale within the system.  There is much discussion of thermostats for the LT5.

A word of caution. The LT5's thermostat has several functions. In addition to performing the duties of a thermostat, it also provides a by-pass function for the radiator in the event the amount of coolant exceeds the capabilities of the radiator. Use of the incorrect thermostat can result in blown hoses and even blown apart radiators.

The LT5 is equipped with a 195 degree thermostat but we have also had great results using the Stant 180 degree stat (part #14068). As previously mentioned, the radiator is highly susceptible to restrictions and blockage. This is the main cause of any rise in operating temperatures and should be addressed first. This airflow restriction occurs when particles are collected in the small space between the AC condenser and the radiator and is not visible until the top radiator shroud is removed and the radiator fully viewed from the top. Radiator removal is not as involved as it may first appear and we find that periodic removal and cleaning is very effective.

Also be sure to inspect the AC condenser due to the fact that it is installed in front of the radiator. It too must not be obstructed or possibly damaged by road debris.

As we have said, keeping your LT5 cool and the cooling system serviced are crucial to the LT5's durability. Although there are some larger aluminum radiators available, the stock system should provide adequate cooling under most street operations if kept clean and unobstructed. The LT5 is susceptible to head gasket problems if allowed to over heat because of the close proximity of the lower part of the cylinder to the coolant passage. If your LT5 uses coolant and you see no external leakage, you may have a seeping head gasket and should have it check immediately.

We see little if any. Remember, platinum tipped plugs were originally developed only to increase service intervals. No problem? Then what are you "fixing?"

CAUTION. Improper application of the powder coat can result in terminal damage of your LT5 parts. Some of these are very expensive. Cam Covers, for instance, come only when attached to the $5,000 cylinder head. There are also a variety of types of powder coat with some being more suitable for engine compartment use. Be sure you use a facility very familiar with this type of work.

The '90-'91 model shocks have an internal rod travel of 160 degrees, controlled by the control module located behind the driver's seat in the rear compartment (by the ABS controller). The '92 and up models have only a 80 degree rod travel. Therefore, it is essential that an earlier style controller NOT be used on a later style system or the result will be 4 stripped actuators.

 
Bilstein Gas Pressure Shock Absorbers, due to their extremely high internal pressures, must use a seal which is extremely tight. To prevent deterioration from the friction between the piston rod and seal, a self lubricating seal is used. By design, a small amount of the shock absorber oil is allowed to pass by the seal onto the piston rod, thus creating a constant film of oil on the rod. In fact, approximately 10% of the total oil capacity of the shock is intended for this purpose.

After an extended period of time, this oil will create a blackish film on the shock body. The appearance of this oil is normal and should not be taken to indicate a defective Bilstein shock. This gradual oil loss will not affect the performance of the shock except after a long service life (50,000-75,000 miles) depending on driving conditions.

When the shock's performance is questionable, your Bilstein distributor can have the Bilstein units completely rebuilt and rebuilt units carry a lifetime warranty from Bilstein. In addition, we also upgrade older shocks to the newer dual digressive design and install programmable controllers in which replaceable proms are used for various driving conditions. This allows an owner to have both the comfort of a daily driver and the ability to easily convert to a much more aggressive ride for performance usage.

We've seen some restriction in fuel filter flow in as few as 12,000 miles. The fuel filter is located under the passenger footwell. In addition to the plugs and fuel filter service, we also recommend the cleaning of the PCV valves and throttle body at periodic intervals. We do not recommend using ANY un-approved fuel additives or other methods of injector cleaning as they may damage your ZR1's fuel system.

The original spark plug wires on the LT5 are highly susceptible to wear. This may be as a result of the tight placement under the plenum, their proximity to each other, their construction, or the high energy ignition system itself. We have found wire damage in as little as 20,000 miles. If your LT5 seems less crispy on power or seems a bit rougher at idle than it once did, this is likely a place to start. The replacement wires are identical except they are not marked with "Corvette LT5" as are the originals.

Simulate the vehicle being parked on an incline for 12-24 hours. With the front end higher than the rear, at least 1 foot higher, Try to put it into reverse when it first gets started (cold). Mine wouldn't even go into reverse. I had to coast backwards until level and use 1st gear. (used master, new slave)