Taken from Ciao!NEWS,Volume 2 Number 1, Summer 1995.

X1/9 Cooling Systems
Though Fiat greatly improved cooling system designs by the time the X1/9 was officially introduced in 1974, as the cars grow older, a number of areas need to be watched to make sure this popular Bertone-designed car stays cool running.

First, the condition of the coolant is very important. When the coolant gets over two years old, it can cause the pipes under the car to corrode from the inside out. As with ANY car, the coolant should be changed every two years.

If your X1/9's system has already started to deteriorate, the sludge will accumulate in the cross-flow radiator. Even if properly bled, sludgy radiators will run hot. It's easy to test if your radiator is suffering from this problem. Just check the radiator's temperature at the top and the bottom (use a pyrometer if you have one, or your hand if you still have any feeling below the calluses). A properly flowing radiator will be equally hot at the top and bottom. A sludged-up radiator will stay cool at the bottom while the top heats up. The remedy is to remove the radiator and have it rodded by a reliable radiator shop, but, given the age of these cars, be prepared for the cost of recoring it if it's too far gone.

The water pump belt on non-air conditioned cars is another tricky area. Mechanics unfamiliar with X1/9s will do it wrong everytime: the proper size water pump drive belt must be forced on; one that slides on easily will be too long and will not adjust properly. Air conditioned cars have so many variations, all I can really say is that the belt should be properly tightened, in good condition, and should be changed every two years (along with the timing belt, both on AC and non-AC cars).

An X1/9 motor that is leaking oil will contribute to cooling system problems. The oil drips onto the long engine-to-cooling- tube hoses, causing them to swell. The swollen hoses then rub against things they shouldn't. Unaware mechanics may replace these hoses and route them wrong so they STILL rub! And don't forget that just changing the swollen hoses (and routing them correctly) without fixing the original oil leak will only be a temporary fix.

Bleeding the cooling system properly is also important. But be prepared to remove the radiator, if needed, as the X1/9's bleeder screws are soldered onto the top left of the tank. Due to the age of the solder, these have a knack for snapping off at the most inopportune moment! The surface of the coolant tank where the radiator cap seals also rots with age, and the plastic tanks tend to leak from their center.

Here's a quick walk-through on bleeding the cooling system.

1. Remove the radiator cap. Pull the small overflow tube hose up above the tank.
2. Fill the coolant bottle with new antifreeze and water in a 50-50 mixture. Check to make sure it's the proper Ph.
3. Start the engine and run at idle. Open the heater valve. If the bypass thermostat is working properly, the engine would warm up to the center of the gauge pretty fast, and stay there.
4. Once the thermostat starts cycling the radiator/cooling-tube water into the motor, open the bleeder screw about one turn or so, to "gurgle" out the air in the radiator. I use a length of 8mm allen wrench that I've cut off to about 25mm long. I stick this into the bleeder, and use my 8mm box-end wrench to open and close the valve easily.
5. As the radiator starts to warm up and the air in the cooling tubes moves, the air will accumulate in the radiator at the bleeder screw. Everytime you open the screw, bleed until you get pure coolant without air dripping into the pan you placed under the radiator. Make sure there's another drip pan under the coolant tank, too. You should be able to observe lots of air at first in the bottle, but as it warms up the air will stop. I like to keep the bottle almost full as I bleed the system.
6. Once the engine coolant and oil are warm, hold the throttle open so the engine runs about 6000 rpm for 30-60 seconds. Besides sounding loud and crazy, this forces the air out of the heater core. You can confirm this as both the in and out heater tubes located on the inside of the right footwell will feel hot to the touch. Revving the engine will also force the air out of all the nooks and crannies of the cooling system. Bleed the radiator some more, and top up the bottle.
7. The radiator fan(s) should come on when the outlet side of the radiator reaches 92 degrees C, and go off at 89 degrees C. This is just past 190 degrees F on the temperature gauge. If your fans don't come on and the gauge goes up close to the red, something's wrong. Stop the motor and find out what. Be prepared when you shut it off--heat soak with the coolant bottle cap off will cause the coolant to boil.
8. Once the fan comes on you'll see how water expands when hot and contracts when cool, as the coolant level in the tank rises and falls with the fan. Don't open the bleeder screw on the radiator with the fan on, as the contracting coolant will suck air IN, and you don't want any air in there!
9. About ten seconds after the fan goes off, open the bleeder screw on the radiator. Once you get no air for two cycles, tighten down the bleeder screw, top up the tank as the fan goes off, and put your radiator cap on. Push the coolant hose back down where it belongs--yes, it will spurt some coolant until the system settles at its natural level, but start off full so there's still plenty when the coolant contracts after you turn off the motor. Make sure that no air enters the system anywhere other than the overflow hose. A single defect can lead to overheating.

   Bleed the system with every tune up (preferably every 8,000 to 10,000 miles) to protect your otherwise reliable SOHC motor.

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