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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
May 1, 2002
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1985 Chevy Corvette Z51 Cooling Overhaul - Oh So Cool
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.
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.
To remove the fan shroud, you must first move the power steering reservoir. You can simply move it to the side to get a little extra room while working.
These little devils are a common problem on C4s. The metal tabs in the fiberglass shroud often strip the slot in the fiberglass, allowing the tabs to spin around when you attempt to remove the air box. Trying to remove an un-anchored stud can be a nightmare. One way to cure this problem is to pop rivet the metal tabs to the fiberglass to ensure that they will stay in place.
This is the new thermostatically controlled fan switch. The location of this switch can vary between build dates within cars of the same model year.
To take the radiator out, you will have to remove all the shrouding that holds it in place.
You can see one reason why this '85 ran a little on the warm side. Once the radiator was removed we found a 17-year accumulation of tree leaves and other debris stuck between the radiator and the A/C condenser. We cleaned all this out, of course.
The other side of the new fan switch will plug in where the old one came from. Using the supplied connectors you will have to splice one new wire into the new plug. This will allow both fans to come on at 180 degrees.
On the opposite side of the new fan switch is this new relay. It screws on the cowl (in the engine compartment), just under the windshield on the driver's side. Notice we had to splice one new wire on this side also.
To get to the water pump you need to remove all the accessories, starting with the smog pump. To remove the smog pump, you first need to remove the pulley, then the pump itself, followed by the alternator.
If you're planning to change the water pump, it's now time to remove the serpentine belt. Use a short (3-inch) 1/2-inch drive extension to back off the tensioner, then pull out the belt. As you can see, the belt is also worn out. Don't worry-we replaced that, too.
When we removed the smog pump we found that the rubber hose on the back of the pump had started to deteriorate, so we went ahead and replaced it when we re-assembled the '85.
With the left-front corner of the L98 stripped bare, it was time to unbolt the old water pump and replace it with the new OEM replacement. The old water pump was actually in decent condition, and is now sitting on a shelf, as a spare.
These are the new and old lower radiator hoses. The spring is dead on the old one, and the rubber has gotten soft and started to fray.
Next we replaced the thermostat. The thermostat housing (arrow) is below the throttle body and is attached with two bolts. It's not an easy task, but thermostats corrode and clog up, even when the car isn't used a lot, and it's easier to install a new one when the accessories are already out of the way.
This is why we got started on this project-the original fan motor had gone bad. Once we thought about it, it just made more sense to freshen up the whole system.
Use a little grease on the inside of the lower radiator hose to help it slip onto the water pump outlet easier. Slip a hose clamp onto the hose before you install it.
To remove the lower baffle (air ducting) you have to take the bolts out from both below and on top. From the top side you first have to remove the overflow tank to reach the bolts. You have to be somewhat creative to do this; you don't have a ton of room to work with.
From underneath, we removed the fasteners that hold the lower baffle and spoiler in place.
The entire lower assembly centersection of the Z51 front spoiler, which is attached to the lower baffle or duct by a "baffle retainer," will slide out the front in one piece. (The arrow indicates the torn corner.)
Once the spoiler and lower baffle assembly is out, strip it of all the hardware. You will need all of it to install the new lower baffle and to put the assembly back in the car.
Once all the hardware has been removed, we pulled the "radiator grille mount panel" out and set it aside. It will be re-used.
We started the re-assembly of the lower baffle and spoiler by pop riveting the metal baffle retainer to the plastic lower baffle or duct. This both supports the baffle and holds it to the spoiler. You will also have to pop rivet the new inner radiator grille brackets in place. Make sure you have them positioned correctly; if they're not, the radiator grille mount panel will not bolt up properly.
Now it's time to slide the new lower baffle assembly into place. You will have to get a little creative to get it bolted up correctly.
Here is our old, torn-up lower baffle next to the new one after the retainer and inner brackets had been attached.
This broken piece (arrow) is what's left of the center radiator grille bracket, the part that provides support between the spoiler and the grille mount panel. The replacement piece is much stronger, thanks to a redesign by GM while the C4s were still in production.
Here is the completely re-installed spoiler and lower baffle assembly, with the grille mount panel also in place. Not only does it help with better cooling, but also it looks much more appealing than the torn-up parts did.
Back on top, we now set the new radiator into place. This new radiator is a direct replacement for the stock unit, so it falls right in place.
Because it's a direct replacement, all the lines and hoses will hook up to the radiator without any bending.
Next we re-installed the original upper cushion to correctly position the new radiator. The cushion both locates the radiator and works as an isolator, so make sure it gets reused. With the isolator in place, we installed and tightened the fan shroud.
After re-installing the alternator and the smog pump, it's time to put the new serpentine belt on. Using the same 3-inch long, 1/2-inch drive extension as before, we pulled back the tensioner and positioned the belt, making sure that the belt was routed correctly.
When the new upper radiator hose is installed, make sure to use this stock bracket. It acts as a support for the upper hose.
Then we plugged the connector into the new fan motor and attached the fan assembly to the shroud with the same four bolts that we removed earlier.
We next put the mass airflow sensor, air intake tube, and the air box back on, making sure that the air box was sitting level and the air intake tube was tight before final-tightening the air box.
The final step was to add new coolant to the radiator and start the car, allowing it to circulate for a short time. This lets any trapped air pockets get pushed out of the radiator.
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