Here are the basics:
1. Placing the radiator more vertical is best when possible to get natural wind as you drive. If possible, avoid depending solely on electric fans to do your cooling. Try to mount the radiator so it can get a straight shot breeze of air through the radiator as you drive, assuming your car setup will allow this.
2. Radiator fans need high current relays to turn them on and off as your engine management system dictates as the engine warms up. Almost all relays have a tiny pinhole in the bottom as a breather so condensation doesn't build up and rust things when you're in humid climates. In the desert you don't have to deal with humidity, so this hole should be sealed tight so dust and sand cannot enter the contact area. The same is true for your fuel pump relay. If you experience a fan that's non-operational, or a fuel pump that won't run, and you haven't filled these breather holes, just knock the relay with a wrench to shake out the dirt in the contacts. When you get home, replace the relay and fill the breather hole this time!
3. Assuming you mount your radiator vertical like it's should to be, the top water connection is specifically for your engine to RETURN coolant to the radiator. The top radiator hose connects to the coolant exit on your motor, located on the top of a Subaru motor, and typically on the top of the motor all other motors. The bottom radiator hose connection is specifically to PROVIDE coolant to the motor water pump, located on the bottom of a Subaru motor, in the area where the dip stick goes into the oil pan on EJ20 and EJ25 motors. An easy way to remember how to connect the radiator hoses to a Subaru motor is....
"top goes to top, bottom goes to bottom"
4. When routing the coolant lines from the radiator to the motor, it's OK to route the lines left and right to get to where you need to go. But avoid routing the lines up and down with dips and rises to make your connections. The lines should have a gradual and consistent slope from the radiator to your motor.
If you don't follow these simple guidelines to connect radiator hoses your car can be very temperamental when it loses the least amount of coolant. Air gaps in the top of the radiator manifold can promote the introduction of air into the cooling jacket of the motor. When these air bubbles arrive in the super-hot head/barrel area they can rapidly expand and create micro-bursts of pressure in your radiator, potentially blowing up your radiator capillaries like a balloon, eventually leaking.
To prevent air gaps and setup a radiator system for the best efficiency, here are two diagrams below that gives you the basics of what a sandrail needs. Using a burp tank setup helps prevent air entering your system, yet allowing the coolant to expand and contract in volume as the motor heats up and cools down.
The first diagram shows a pressurized burp tank setup. These systems have no filler cap on the radiator, you add coolant through the burp tank filler cap. When you initially fill the system from the burp tank, the coolant enters the engine via gravity through the hose that's connected the heater return connection of the Subaru motor. Since sandrails don't have heaters, this connection works great to fill the motor via gravity. Air escapes through the Air/Water Bleed hose on the radiator as the coolant pushes it out. After the coolant fill up motor water passages so the level is even with the top of the radiator, start up the motor and bring the motor up to full temp, about 180 to 200F. As the water heats up the excess coolant will expand and escape through the overflow tube. The remaining fluid will be the correct amount of coolant for the system. After the motor cools down overnight, take a note about where the coolant level settles inside the burp tank, viewed through the filler cap. Some folks will mark that level with a felt marker on the side of the burp tank so they can remember the "normal level" when cold.
For new motors it's a good idea to check the level on the first few weekend trips, when cold, to insure it's at the correct level. Generally speaking the burp tank coolant level should settle down to about 1/2 to 2/3 full when cold.
The setup below is an example of an UN-pressurized burp tank setup, which is more conventional. It's important to know this setup requires:
1. If you run a thermostat (not recommended for sandrails) in your engine you must connect the engine water heater connection (located on the thermostat housing) to the water crossover tube on top of the motor. As the engine warms up this provides hot water to the thermostat, triggering the thermostat to open.
2. If you don't run a thermostat (recommended) you can block of the water heater connection, located on the thermostat housing. To remove the thermostat you'll need a substitute thermostat ring to hold the thermostat gasket (available from Outfront), which prevents the thermostat housing cover from leaking.
The above setup with an un-pressurized burp tank allows more flexibility in locating the mounting place for the burp tank. Sometimes this is a problem in some chassis', making this setup more desirable. In this arrangement requires a filler neck on the radiator to fill the system with coolant. This arrangement requires that you always fill the radiator from the RADIATOR filler cap, not the burp tank as described above with the pressurized setup.