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1985 Chevy Corvette Z51 Cooling Overhaul - Oh So Cool

A Cooling System Rehab Helps An Early C4 To Cruise 25 Degrees Cooler

Seth Millhollin May 1, 2002
Vemp_0205_01_z 1985_chevy_corvette_z51_cooling_overhaul Air_box_removal 2/36

We started by removing the air box. Once it is off, we also removed the air inlet duct and mass airflow sensor (they run between the air box and the throttle body). The throttle body doesn't need to be removed.

Over the years, the cooling system on any Corvette will no longer work as well as when it was brand new, due to a number of factors. Corrosion builds up inside the radiator and within the engine. The rubber hoses and lines will start to fray and flex, and at the least expected moment, they'll usually spring a leak. Furthermore, the factory radiator is not as efficient as it used to be, and on cars like C4s, the lower air ducting has more than likely been bashed and torn into oblivion. The components of a system like this have certainly seen better days. Well, how would you like to see a 25-degree temperature reduction this coming summer?

C4 Corvettes were introduced almost 20 years ago, and almost nothing can go that long without being replaced. With the passing seasons the coolant has probably deteriorated the aluminum radiator (unless you've been diligent enough to flush the cooling system per the owner's manual) and caused it to corrode, and now your ride is certainly running hotter than you would like. That's the case on our subject car, a low mile, fairly well-maintained '85 that was starting to run too hot, too often. So when the electric fan stopped working, we decided to "R & R" the entire cooling system. We ordered all the components (see parts list at the end of this article) from Mid America Designs.

Though the trend in the street rod market is to install aluminum radiators in their machines to help cool them down, we replaced the '85 C4's factory aluminum radiator with an aftermarket brass. According to the folks at MAD, the brass unit will help dissipate the heat better in an average daily driver. Another obvious reason enthusiasts are using aluminum radiators are for weight savings. Of course, in a race car this is an important factor, but for a boulevard bruiser (or cruiser) the minute difference in weight saved by the aluminum radiator over a brass one is insignificant. However, as we found out, the cooler temps we got were a big improvement.

In order to make sure the complete cooling system on our '85 (which happened to be a Z51 option car with both the standard pull-through and auxiliary front-mounted "pusher" electrical fans) would perform to its potential, we also installed a new thermostat fan switch, which is designed to turn on both electric fans when the temperature reaches 180 degrees. This will ensure that coolant stays at or near this temp during those hot days in traffic. Installing the new switch in the car was a snap, but it was necessary to wire it through the OEM relay so it won't blow a fuse by turning on both fans at once.

Vemp_0205_03_z 1985_chevy_corvette_z51_cooling_overhaul Electrical_plug 3/36

There are four bolts (one in each corner) to be removed in order to take the fan out. There is also an electric plug that you must disconnect; it is on the lower side of the fan motor.

All '84-89 Z51s came stock with dual electric fans (the "pusher" fan was available separately as RPO B4P on '86-89 C4s); the only bad side to this setup was that they came on at different times. It was never enough cooling at once, and by the time the auxiliary fan (GM described it as a "radiator boost fan") came on, the motor had built up more heat. It was an ongoing cycle that left these cars running at about 220 degrees-more than most of us want to see on the temp read-out.

Other major parts we upgraded were the electric fan motor, the water pump, thermostat, and all requisite hoses.

The factory water pump, also an aluminum component, is subjected to some of the same conditions that can corrode an OEM radiator. But unlike the benefit of switching to the brass radiator, there is no need to put anything other than an original water pump back on if yours leaks or the "impeller" is going bad. If the fins on the impeller are no longer in good condition, the pump will not circulate as much water. The less water that is circulated, the hotter the engine temperature will be, and we all know that is not a good thing. Another thing that will immediately tell you that you need a new water pump is a noisy bearing. The bearing can sometimes go bad long before the coolant corrodes the inside of the housing or the impeller. Those of you with cars that have a lot of miles on them want to be especially aware of this.

Vemp_0205_07_z 1985_chevy_corvette_z51_cooling_overhaul Radiator_removal 7/36

To take the radiator out, you will have to remove all the shrouding that holds it in place.

The subject car was in very good condition and had fairly low mileage. For this reason the water pump we took off was in excellent condition and will be stored to use as a spare. Some of the other items (radiator hoses, vacuum hoses, etc.) will deteriorate just from getting old, much like the ones on this car. All the hoses were starting to get soft, and the radiator was definitely clogged by corrosion. The lower baffle (air duct) was also a large part of the problem on this '85. Actually, it was more of a lack thereof. The ducting was in very poor shape and probably wasn't directing a whole lot of air where it was supposed to go.

The passing of time will cause some parts of any car to go bad. It is extremely difficult to keep your Corvette "feeling" young, but it can be done. You can and must make sure it receives the correct treatment for any ailment it may acquire. That is why we installed a brand-new cooling system in this '85, instead of just replacing a worn-out electric fan motor. That is also why instead of running at 215 to 220 degrees, it now runs at a consistent, and oh-so-cool, 180 degrees.



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