Coolant filling procedure
Coolant filling procedure is the procedure used to refill and bleed the Pontiac Fiero cooling system.
Because the Fiero has a mid-mounted engine, a front-mounted radiator, and long coolant pipes running underneath the car, the cooling system must be filled carefully to avoid trapped air.
Overview
The Fiero cooling system is different from many front-engine cars. The radiator is at the front of the car, while the engine, thermostat housing, and rear fill point are at the rear.
If the system is filled incorrectly, air can remain trapped in the cooling system. This can cause overheating, unstable temperature readings, coolant overflow, poor coolant circulation, or repeated coolant loss.
A properly maintained Fiero cooling system should not overheat. If overheating continues after proper filling and bleeding, another cooling-system fault should be investigated.
Why the Fiero is different
Most front-engine cars have the engine and radiator close together. The Fiero does not.
The Fiero cooling system includes long coolant pipes running under the car between the rear-mounted engine and the front-mounted radiator. This makes trapped air more likely if the system is not filled correctly.
The system should normally be filled from the thermostat housing at the rear of the car, not only from the radiator at the front.
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Applies to
This article applies generally to all Pontiac Fiero model years:
Details may differ by engine, model year, thermostat housing, radiator cap, cooling-system condition, and previous repairs.
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Safety
Only open the cooling system when the engine is cool.
Hot coolant is pressurized and can cause serious burns. If the engine has overheated, allow it to cool completely before removing the radiator cap, thermostat cap, or any cooling-system part.
Do not run the engine unattended during filling or bleeding. Watch the temperature gauge and shut the engine off if the temperature rises abnormally.
Tools and supplies
Useful tools and supplies may include:
- Correct coolant mixture
- Funnel
- Gloves
- Drain pan
- Rags or shop towels
- Flashlight
- Replacement radiator cap, if needed
- Replacement thermostat cap, if needed
- Replacement thermostat, if needed
Before filling
Before filling the system, inspect:
- Coolant pipes under the car
- Radiator condition
- Radiator cap
- Thermostat cap
- Hoses and clamps
- Water pump
- Thermostat
- Coolant overflow bottle
- Visible leaks
Damaged or crushed coolant pipes can restrict flow and cause overheating. This is a common Fiero-specific issue, often caused by incorrect jacking or lifting.
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Vehicle position
The car may be parked on level ground.
Some owners prefer a slight nose-down position, with the front of the car slightly lower than the rear. This can help move trapped air toward the thermostat housing, which is one of the highest points in the Fiero cooling system.
Do not use a steep or unsafe slope. The car should remain stable and safely parked.
Basic filling procedure
A commonly used Fiero filling method is:
- Make sure the engine is cool.
- Park the car on level ground, or on a slight slope with the front of the car slightly lower than the rear.
- Remove the thermostat cap at the engine.
- Remove the thermostat.
- Remove the radiator cap.
- Slowly fill coolant at the thermostat housing until coolant reaches the radiator.
- Install the radiator cap when coolant is present at the radiator.
- Continue filling at the thermostat housing until the system is full.
- Leave the thermostat out temporarily.
- Install the thermostat cap.
- Fill the coolant overflow bottle to the correct cold level.
- Start the engine and run it briefly, about 30 to 60 seconds, while watching the temperature gauge.
- Shut the engine off.
- If the engine is still cool or only slightly warm, carefully crack the radiator cap open without fully removing it.
- If air is present at the radiator, it may escape with a hissing sound.
- If coolant spills immediately and no air escapes, close the radiator cap.
- Recheck and top off the coolant level at the thermostat housing.
- Repeat the short-run and radiator-cap air release steps until no air escapes from the radiator.
- Allow the engine to cool completely.
- Recheck coolant level at the thermostat housing.
- Add coolant if needed.
- Recheck the coolant overflow bottle when the engine is cold.
- Reinstall the thermostat once air has been removed and the system level remains stable.
- Check for leaks.
Coolant overflow bottle
The coolant overflow bottle should contain coolant when the engine is cold.
If the overflow bottle is completely empty with a cold engine, air in the cooling system is very likely, because the system may draw air back in instead of coolant as it cools.
A full or partly full overflow bottle when the engine is hot does not prove that the cooling system is free of air. Coolant can expand into the overflow bottle while air remains trapped elsewhere in the system.
When checking the cooling system, inspect both the coolant level at the thermostat housing and the level in the overflow bottle after the engine has cooled completely.
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Burping the system
Burping the cooling system means removing trapped air from the system after filling.
Air may need to be removed over several heat cycles. After the engine cools, the coolant level should be checked again at the thermostat housing and at the overflow bottle.
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Thermostat notes
Many owners temporarily leave the thermostat out while filling and burping the system. This can make it easier to fill the system and remove trapped air.
The thermostat should be reinstalled once the system is full, stable, and free of trapped air.
Running without a thermostat as a permanent fix is not a proper solution to overheating. If the car overheats with a correct thermostat installed, the cause should be diagnosed.
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Radiator cap and thermostat cap
The radiator cap and thermostat cap must seal correctly for the cooling system and overflow bottle to work properly.
A bad cap can allow coolant loss, prevent proper pressure control, or allow air to be drawn back into the system.
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Symptoms of trapped air
Symptoms of trapped air may include:
- Temperature gauge rises quickly
- Coolant overflows
- Coolant level drops after cooling
- Heater performance changes
- Radiator fan operation seems normal but temperature still rises
- Gurgling sounds
- Repeated overheating after refill
- Overflow bottle is empty when the engine is cold
Common mistakes
Common mistakes include:
- Filling only from the radiator
- Leaving air trapped in the system
- Installing the thermostat before the system is full
- Forgetting to refill the overflow bottle
- Assuming a hot overflow bottle means the system has no air
- Using the wrong radiator cap
- Ignoring crushed coolant pipes
- Assuming overheating is caused by the thermostat without checking for air
- Opening the system while hot
- Overlooking leaks
Diagnosis if overheating continues
If the car still overheats after proper filling and burping, check:
- Coolant pipe damage
- Radiator fan problems
- Thermostat problems
- Water pump failure
- Radiator cap
- Blocked radiator
- Temperature gauge problems
- Coolant leaks
- Air in cooling system
Notes
A properly maintained Fiero cooling system should not overheat.
Repeated overheating after filling usually indicates trapped air, coolant loss, restricted flow, fan problems, cap problems, water pump problems, or another cooling-system fault that needs diagnosis.
Do not continue driving a Fiero that is overheating. Severe overheating can damage the engine.