Maintenance

ZR-1 Maintenance Tips

Last updated 10/1/04

ZR-1 Diagnostic Tools, Testers and Books can be found at "FOR YOUR CAR, Inc."

General Maintenance by Jim VanDorn

The most common call we receive by far is from a confused ZR1 owner. After years of reading everything from which thermostat to use, to what type of spark plug is best, the average owner is totally and completely confused...and for good reason. There are many varied opinions of what is best for our cars but that may depend greatly on how you use your ZR1.

After seven years plus, many ZR1's are finally accruing some mileage. We have had the opportunity to closely inspect many engines with a variety of types of use from normal street driving to severe "weekend" use (track time). Compiling this information we can now offer the ZR1 owner some observations. One rule we've adopted after hearing so many owners say the same thing is the "DIMWIT" or "Darn, if I didn't Mess With IT" rule. In other words, if you didn't have a problem, then what are your intentions in the first place? To date, the only company known to have a fleet of engineering ZR1's to test with was GM and it's affiliates. Therefore, we must ask ourselves if their suggested procedures and parts recommendations should have a considerable amount of merit. Obviously they do, but on the other hand, there are no doubt areas for improvement. Although we will begin our segment discussing the routine and normal maintenance of the ZR1, there are many areas where an upgrade will be suggested.

Please understand that these are personal opinions and experiences and are not intended to conflict with service procedures outlined in the appropriate service manual.

Cooling System Service	Maintenance Oil	Air Filters	Other Lubricants/Fluids
Cooling System	Spark Plugs	LT5 Cleaning and Appearance	Shocks
Tune Ups	Checking master hydraulic clutch cylinder

COOLING SYSTEM SERVICE

Drain, flush and refill system with new coolant as follows:

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.

L. Check level in recovery reservoir and add coolant to full "HOT" mark on dipstick.

Maintenance Oil

The most common form of preventive maintenance is the routine oil change. If you drive your car in hot weather, or under severe track conditions (high RPM and high cornering situations) then a good synthetic oil is highly recommended. Redline, Mobil, and others meet OEM standards. If your car is street driven, then use the oil recommended in your owner's manual. Find a name brand and stick with it when possible as several quarts of oil remain in the cooler and is not removable during a routine oil change. 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.

Air Filters

The AC air filter is of the highest quality but must usually be serviced at much greater intervals than the 30,000 miles indicated in the owner's manual. The K & N is also a highly popular replacement. The K & N costs that of two AC's but is a reusable filter which can be cleaned with a solvent and oil treatment at periodic intervals. There have been some problems reported with the K & N's ability to seal within the filter housing. A foam strip kit is included with new K & N filters to ensure a better fit. Be careful not to install a "wet" K & N after the cleaning treatment.

Other Lubricants/Fluids

Depending on your driving habits and conditions, we recommend the following. Street driven cars can adhere to the recommended lubricant's and service intervals, but the more aggressively driven ZR1 can benefit from a change to the synthetics. Synthetics basically provide better lubrication and have extended ranges of effective operation. ZR1 systems which benefit from synthetics are the power steering, differential, radiator and some transmission applications. 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.

Cooling System

By far, the most common complaint made by the Corvette owner is "overheating." There are several concerns here. 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.

Spark Plugs

It seems the items most easily accessible to the owner are also the most popular to change. We've all heard the claims of better and more, but the truth is this. Why fix something that isn't broke? In other words, why change brands from the recommended type of plug if you are experiencing no problem? The 90-92 LT5's were equipped with a conventional (flat seat w/washer) spark plug, the FR2LS. In '93, the platinum tipped (tapered seat) plug was installed. The later style plug can be installed in the earlier engine by basically "forcing" the plug (over torqueing by 25ft lbs the first time) into the head thus creating a tapered seat. Question is, what benefit are platinum tipped spark plugs over conventionals? We see little if any. Remember, platinum tipped plugs were originally developed only to increase service intervals. No problem? Then what are you "fixing?"

LT5 Cleaning and Appearance

Some of you have found out the hard way that the LT5 engine is not "cleaning friendly." IN fact, we would more likely say that the LT5 is a real challenge in more ways than one. First of course, the LT5 cannot be rinsed down with water or the puddling within the intake valley will damage your starter resulting in a $600 repair bill. Secondly, the LT5's finish is not a very durable one to say the least. Although similar powder coat was used on all year models, you may have already noticed a change in the appearance of your LT5. This change can be caused by several factors including UV damage, improper use of cleaning solutions, and reactions to underhood chemicals including coolant, oils, and brake fluid. Cleaning of the LT5 should only be accomplished when absolutely necessary by using a damp towel and MILD soap solution such as dishwashing soap or Simple Green. Remember, the LT5 paint is readily damaged by harsh chemicals so the milder the better. In the event your engine's finish is already damaged or simply suffering the adverse effects of time, there are some remedies. There are some spray paints out there that can be applied but obviously are not very durable. The other choice is to have your competent technician carefully remove approximate labor charge of 8-10 hours) the visible components (cam covers, injectors housings, water outlets, plenum, throttle body and air horn) and have them re-powder coated by an experienced powder coater. 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.

Shocks

As with many other systems on the ZR1, constant improvements were made each year to enhance handling performance. With the exception of the '95 model year, the ZR1's shock valving and calibration was changed every model year. In 1992, the factory Bilstein shock absorber was changed dramatically from a single piston design to a "dual digressive" or two piston per rod design. Simply explained, the new valving assembly controls oil flow through the bypass orifice passage and this generated characteristic again becomes digressive. This re-designed provided a wide range of new low speed controllability.
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.

Tune Ups

The LT5 requires much the same routine care as most other engines. As we've mentioned before, unless your car will see severe duty, we highly recommend using original brands and types. The stock AC spark plugs perform beautifully and should be replaced at 15,000 to 20,000 mile intervals, and although there has been much discussion of switching to platinum (etc.), type plugs, there is little documentation to prove any performance increase other than a longer service life.

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.

Checking master hydraulic clutch cylinder

Here is a method of testing the condition of the master hydraulic clutch cylinder after the slave cylinder has been replaced.

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)