1973 Chevrolet Corvette - Shark Bites

'68-'82 Corvette Tech

Chris Petris Nov 1, 2007 0 Comment(s)

The fan clutch regulates how much fan lock-up is occurring to limit engine drag at highway speeds. There is no need or limited need for the cooling fan after 45 mph is reached unless you have airflow or engine performance issues. The original fan clutch is a thermostatically controlled unit that should have maximum fan speeds at low engine speeds above 180 degrees. When the engine is cold, the fan should have very little drag. As engine temperature increases so should the drag. When the engine is fully warmed up, the fan should stop almost immediately when the engine is shut off. If the fan keeps spinning, the clutch is bad. Another test is when the engine is hot, shut the engine down, grab the fan, and try to turn it. You should feel noticeable resistance, if not, the clutch is bad.

In addition, there are other factors that may affect cooling: water pump impellers can deteriorate; a wrong pulley size can affect low-speed cooling; improper antifreeze/water mix can increase temperatures. We use the 50/50 rule for mixture for freeze protection in northern climates. In the southern states, you only need to worry about worst case scenario. The 60-percent water/40-percent antifreeze is adequate freeze protection and will help dissipate more heat. In your area (Florida), 70-percent water and 30-percent antifreeze would be fine and is the most dilution you should go with because other engine protection additives would be too low.

As you can see there are many variables and possibilities to consider when cooling issues arise. Hopefully, this will get you cool again. the A/C won't be cool until the engine it relies on has good air flow through the A/C condenser in front of the radiator. Additionally, a hot engine compartment makes it difficult to cool the passenger compartment.

I have owned a '75 coupe for the past six years. it has all the options offered in 1975; it's one of 144 with the Z07 option. Recently two issues have developed: 1) The driver-side headlight assembly won't open; the passenger side is ok, so where do I begin to fix this? 2) The passenger-side power window won't go down. I found if I push down on the window while activating the switch, it will usually go down. It does work in the up position.
Larry, Two Rivers

The headlight issue has a few possibilities, both vacuum leak related. Either the actuator relay valve has an internal leak, or the headlamp actuator has an external leak. With one headlamp working, it tells us that the rest of the system is working properly and the problem is in one area. The headlamp actuator relay valves are mounted on the underside of the headlamp reinforcement between the headlamps at the front edge of the hood opening, with one valve operating one headlamp independently. You can remove the vacuum hoses from the relay valve in question for diagnosis. The yellow-striped center hose is the vacuum supply. The upper red-striped hose is headlamp close, while the lower green-striped hose is headlamp open. A quick check of actuator operation is easy. Use a short piece of quarter-inch tubing to connect the yellow center hose to the lower green hose. The headlamp should open. Then connect the upper red hose to the yellow hose, and the lamp should now close. If the headlamp now opens, the relay valve is the offending part. If not, the actuator rod seal is most likely torn.

Actuator rod seals require actuator removal to replace them correctly. In a pinch, the seals can be replaced with the actuator in the car, but the dust seal can't be installed properly. The task isn't too difficult. The balance springs are the most difficult to remove. Make sure you have a good hold on them when popping them on and off. Once the balance springs are off, the pivot pin can be removed that connects the actuator rod end to the assembly. Then the four half-inch nuts can be removed to remove the actuator. The rod-end seals and dust boots are available from Corvette Central in kit form (actuator seal kit PN 443012, $24.95), which consists of the seal, dust boot, and retaining ring.

As far as the window is concerned, the window regulator teeth are worn at the top end, which explains why you can get it started and it goes down. When the window is going up, momentum takes over and it raises itself fully. You have a few choices here. Replace the regulator completely or use the repair kit that has the gear and pin necessary to repair the original. It's not too tough to do with the right tools (vise, big hammer, or hydraulic press). There's also a gear repair that goes over the original gear. Either way the regulator must come out for the repairs.


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