Zip Corvette Parts Blog

  • Corvette ZDDPlus Oil Additive for 1953-1972

    As part of an effort to reduce vehicle emissions, automotive manufacturers have pressured their oil suppliers to remove substances from motor oils that would shorten the service life of catalytic converters, including the proven EP (extreme pressure) additive ZDDP (zinc Dialkyl-Dithio-Phosphate). Zinc and phosphorus from the ZDDP can be present in small amounts in the exhaust gas of an engine depending on the amount of oil that is consumed in combustion. These elements can coat the catalyst reducing the amount of catalyst exposed to the exhaust gases, ultimately increasing emissions at the tailpipe. As a result of the EPA mandate, the ZDDP level in engine oils has been declining since the mid-1990s, roughly coinciding with the implementation of OBDII.

    ZDDPLUS Oil Additive ZDDPLUS Oil Additive

    ZDDP has been an important additive to engine oils for over 70 years, and has an excellent track record of protecting the sliding metal-to-metal cam lifter interface. Historically, ZDDP has been added to oils in amounts resulting in approximately 0.15% phosphorus, and 0.18% zinc. ZDDP protects by creating a film on cams and flat lifter contact points in response to the extreme pressure and heat at the contact point. The film of zinc and phosphorus compounds provides a sacrificial wear surface protecting the base metal of the cam and lifter from wear. In the course of normal service, this conversion of ZDDP to zinc and phosphorus compounds depletes the ZDDP level in the oil. Studies show that depending on the specific engine and severity of duty, after 2000-4000 miles of operation, the level of ZDDP can drop below that considered adequate to provide wear protection to the cam and lifters.

    According to the SAE Tech Bulletin # 770087 [1], operation of a flat tappet engine without adequate EP additives such as ZDDP quickly leads to lifter foot scuffing and cam lobe wear. Camshafts are typically only surface hardened leaving the core ductile for strength. According to the SAE Bulletin, once cam lobe wear reaches 0.0002, "subsequent wear is usually rapid and catastrophic." Two ten-thousandths of an inch is one-fifth the thickness of an average human hair.

    In order to make engines last in the absence of ZDDP, virtually all IC (internal combustion) engines designed in the last ten years utilize roller lifters. Today, ZDDP has been removed from practically all automotive engine oils, rendering them unsuitable for use with older engines with non-roller lifters.

    ZDDPlus is the ONLY EP (Extreme Pressure) component that re-establishes the ZDDP levels that our classic car engines were designed for, while allowing the car owner to use the base oil of their choice. It can be used on any flat tappet engine that does not use catalytic converters.

    Purchase online at Zip Corvette Parts

  • Corvette Restoration Tip: Wiring Harnesses

    This Corvette Restoration Tip is brought to you by Zip Corvette and can be found in Zip's free Corvette Parts & Accessories Catalogs - request one online today. Most Corvette owners – or car owners in general – have no idea that the parts in their car have an expected service life. Did you know the service life of a Corvette's wiring harness is only 10 years? That means the wiring in your Corvette was built to last 10 years, not the 40 or even 50 years many Corvettes have been on the road. Individual wires within a harness are made of copper strand housed in plastic.

    Over time, the plastic deteriorates and becomes brittle and cracked, allowing moisture to get into the wire. In turn, the copper corrodes. Ultimately, this process could end in disaster, i.e., corroded wires lead to short circuits – and short circuits have the potential to turn into electrical fires. With vintage Corvettes continuing to climb in both sentimental and monetary value, why gamble on the (usually unseen) condition of an old wiring harness? Cost-wise within the scope of a comprehensive restoration, the fractional expense of new wiring harnesses is your best money spent. Zip’s Corvette wiring harnesses are correct reproductions featuring the same connectors, wire sizes and colors as the originals. Experience new found confidence in your Corvette's electrical system with all-new harnesses from Zip Corvette!


    Purchase new, exact reproduction wiring harnesses for many Corvettes online at Zip Corvette Parts

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  • Is my original 1967 Corvette radio to blame for malfunctioning dash lights?

    Today's Zip Corvette technical question comes from a 1967 Corvette owner:

    I own a 1967 Corvette convertible. When I turn on the radio, my dash lights go out immediately. FUSE BLOWN! I have checked most of the wiring for bare wires, but no luck to date. Would it be something in the radio itself? It is an original radio and it has never been touched. Thanks, I really miss those dash lights.

    63-67 Corvette 1963-1967 Corvette

    Answer: With electrical issues, it can be very difficult to find the culprit. However, with the symptoms you described, I would lean towards a short in your Corvette's radio. You have an interior light that is inside the radio on a midyear Corvette and I feel confident that you have a short in that circuit. The fact that the radio has not been rebuilt also makes me think the radio is the problem because it is 41 years old. The life span that GM put on the wiring in the car was originally 10 years, so I can't imagine that it was much more or even less from the other components in the car. I think it would be best to have the radio restored. Then, you may want to consider replacing your Corvette's wiring harness if that has not already been done.

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  • Corvette Headlight Knob for 1984-1989 C4

    1984-1989 Corvette Headlight Knob Corvette Headlight Knob

    Though it may not seem like much, this C4 Corvette Headlight Knob is a great replacement for 1984-1989 C4 Corvettes. Other replacement headlight knobs will require the headlight switch to be removed, which means the dash has to come out resulting in hours of hard work just to replace the knob. This can be very time consuming and frustrating for something so small as a cracked or faded headlight knob so Zip Corvette now offers this newly designed headlight knob for C4 Corvettes. Now available from Zip Corvette products, this headlight knob will fit onto the original shaft allowing for a quick and easy install.

    Now available to purchase online from Zip Corvette Parts:

    1984-1989 Corvette Headlight Knob

  • Why won't my C4 Corvette's cooling fans turn on?

    Today's Zip Corvette technical question comes from Jim, who owns a 1990 Corvette:

    I have a 1990 Corvette convertible with 350 and 6-speed that I can only drive when the weather is cool because I cannot get the cooling fan to run. The fan motor is good (works when voltage is applied) and I have replaced all of the temperature sensors and the cooling fan relay, but still no fan operation. What else could be preventing the fan from running?

    Answer: Your Corvette's main cooling fan is controlled by the PCM. The PCM sends a ground signal to the fan relay when it sees the desired temperature to run the fan has been met. You need to check the relay and make sure you are getting your battery 12V and ignition 12V when the key is on. With the key on, jump the ground wire in the relay. If the fan turns on, you have an issue in the PCM and it may be time for a rebuild. If it does not turn on, then your problem lies in the fan circuit between the relay and the fans.

  • Where is my Corvette leaking water?

    Today’s Zip Corvette technical question comes from Elliott, who owns a 1981 Corvette:

    Hi, I own a 1981 Corvette that is giving me a problem. When it rains, the carpet under the front floor mats gets soaking wet. The leak is not coming from the top of the car; I’ve sat in the car while it was raining and no water was coming in from the top. Do you have any idea were this leak is coming from?

    Answer: Unfortunately, water leaks are a very common problem with many C3 generation Corvettes. The windshield frames do not drain water properly and water and debris collects in the channels under the exterior moldings, creating a perfect environment for corrosion to take place.
    The water leaks are caused by either a poor seal/installation around the windshield or corrosion that has taken place in the windshield frame itself. The easiest way to check is to look at the frame between glass and the windshield molding. You can see if the frame has rust scales and shows signs of deterioration. There is no easy fix for the windshield frame. To properly fix, your Corvette's windshield must come out and the entire frame needs to be cut out and repaired with new sections. Fortunately, these pieces are available. If the problem is a seal, then you can contact your local glass company to come out and cut the windshield out of the car, reseal the glass and install.

    Purchase online at Zip Corvette Parts

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  • Corvette Restoration Tip: Exhaust Manifolds

    This Corvette Restoration Tip is brought to you by Zip Corvette and can be found in Zip's free Corvette Parts & Accessories Catalogs - request one online today.

    Cast iron exhaust manifolds will begin to rust at the first sign of moisture, leaving your Corvette's engine compartment looking decidedly less than "Best of Show". Begin removing the manifolds by first liberally spraying all bolts with penetrating oil. Repeat this step at least three or four times over the next hour. The last thing you want is a stud twisted off into the base of your manifold – have patience and take your time with the following steps.

    Corvette Exhaust Manifold Corvette Exhaust Manifold

    Once all bolts are well soaked, loosen the three manifold to pipe stud nuts. With a wire brush, clean the stud under the nut and apply more penetrating oil. Now you can slowly remove the nuts. Next unbolt the manifolds from the head (these bolts are grade 8 and rarely cause problems). Bead blast or wire brush the manifolds to clean off all traces of rust, then wipe them down using a small amount of lacquer thinner. Do not wash the manifolds as cast iron absorbs water. After cleaning, apply Calyx manifold dressing. The secret to applying this cream is to slowly rub it into the manifold, working it down into the pores of the cast iron. Do not use too much, as you only want to change the color of the piece. Reinstall the freshly restored manifolds, step back and admire the results!

  • How do you remove the speedometer on a 1968-1977 Corvette?

    Today's Zip Corvette technical question is one that has been asked over and over by 1968-1977 Corvette owners:

    How do I remove my Corvette's speedometer?

    Answer: While you can see the entire speedometer and tachometer in your C3 generation Corvette, removal is not easy. Due to space constraints, steering column placement, main wiring harness routing, vacuum hose connections and speed/tach cables, just sliding up under the dash and removing the gauges are not possible. The first step is dropping the column. No reason to remove the column, just remove the bolts that hold the column to the underdash support and allow the column to “lay down”. Next you can disconnect the speedometer and tach cable connections on the back of the gauges. These cables are attached with knurled nuts in 1968 and then in 1969 through 1977 a spring clip was used to hold the cable to the back of the gauge mechanism. Next, remove the screws on the LH side next to the door jamb, screws holding the lower dash to the upper dash, and several screws coming in from the side on the center cluster bezel. Once the dash pad is worked loose, vacuum connections can be disconnected, vent ball duct disconnected, harness plugs for the headlight switch removed, clips holding the main wiring harness can be undone and the dash light bulbs removed from the back of the gauge housings. The lower dash pad can now be placed in a position for removal of the speedometer and tachometer. Both gauges attach to the back of the dash pad with several screws, upon removal you now have access to either replace or rebuild. Be careful with all components involved, the dash pad and speed/tach housing bezels are plastic and tabs easily break on plastic that is over 30 years old.

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