Thermostat
Thermostat refers to the coolant thermostat used in the Pontiac Fiero Cooling system.
The thermostat helps control engine warm-up and operating temperature by regulating coolant flow through the cooling system.
Overview
The Fiero thermostat is part of the engine cooling system. It remains closed or mostly closed when the engine is cold, helping the engine warm up more quickly. As coolant temperature rises, the thermostat opens and allows coolant to circulate through the radiator system.
Because the Fiero has a rear-mounted engine and front-mounted radiator, the thermostat also plays an important role during coolant filling and burping.
Location
Image wanted: Photo or diagram showing the Fiero thermostat location in the thermostat housing. Ideally include both the 2.8L V6 and 2.5L four-cylinder thermostat housing locations.
The thermostat is located in the thermostat housing in the engine compartment.
The thermostat housing is also used as one of the main fill points for the Fiero cooling system.
The exact thermostat housing location and appearance depend on engine and year.
Function
The thermostat controls coolant flow based on temperature.
When the engine is cold:
- The thermostat restricts coolant flow.
- The engine warms up more quickly.
- The ECM sees warm-up behavior through the Coolant temperature sensor.
When the engine warms up:
- The thermostat opens.
- Coolant circulates through the radiator.
- Engine temperature stabilizes if the cooling system is working correctly.
Relationship to coolant filling
The Fiero cooling system is commonly filled from the thermostat housing.
During filling and burping, the thermostat is often removed so coolant and trapped air can move through the system more easily.
Related topic:
Common problems
Common thermostat-related problems include:
- Thermostat stuck closed
- Thermostat stuck open
- Incorrect thermostat installed
- Thermostat missing
- Damaged thermostat seal
- Thermostat not seated correctly
- Wrong temperature rating
- Corrosion or debris in the thermostat housing
- Incorrect cap or sealing problem at the thermostat housing
Symptoms
Possible thermostat-related symptoms include:
- Overheating
- Slow warm-up
- Engine runs too cool
- Temperature fluctuates
- Poor heater performance
- Coolant pushed into overflow bottle
- Difficulty burping the cooling system
- Erratic temperature gauge behavior
Stuck-closed thermostat
A thermostat stuck closed can prevent coolant from circulating properly through the radiator.
Possible symptoms include:
- Rapid overheating
- Upper cooling-system pressure increase
- Little or no radiator heat transfer
- Temperature rises quickly after start-up
A stuck-closed thermostat should be addressed before continuing to operate the car.
Stuck-open thermostat
A thermostat stuck open can cause the engine to warm up slowly or run cooler than intended.
Possible symptoms include:
- Slow warm-up
- Poor heater performance
- Poor fuel economy
- ECM stays in warm-up behavior longer than normal
- Temperature gauge reads low
Missing thermostat
Some cars may have had the thermostat removed in an attempt to solve overheating.
A missing thermostat is usually not a proper repair. It can cause slow warm-up, poor heater performance, incorrect coolant flow behavior, and diagnostic confusion.
The underlying cooling-system problem should be diagnosed instead.
Diagnosis
Basic diagnostic checks include:
- Confirm whether the engine is actually overheating or running too cool.
- Check coolant level and filling procedure.
- Inspect the thermostat and thermostat housing.
- Confirm that the correct thermostat is installed.
- Check whether the thermostat opens at the correct temperature if testing equipment is available.
- Check thermostat seating and seal condition.
- Check thermostat housing cap condition.
- Check for trapped air in the cooling system.
- Check related cooling-system parts if symptoms remain.
Thermostat housing cap
The thermostat housing cap must seal correctly. A poor cap, damaged sealing surface, or incorrect cap can cause coolant loss, pressure problems, or air entering the system.
Related topics:
Relationship to overheating
A thermostat problem can cause overheating, but it is only one possible cause.
Other common overheating causes include:
- Trapped air
- Low coolant
- Crushed Coolant pipes
- Faulty Radiator fan
- Clogged radiator
- Water pump problem
- Incorrect radiator cap
- Head gasket or engine problem
Notes
Do not assume every overheating problem is caused by the thermostat.
On the Fiero, trapped air and incorrect filling procedure are very common cooling-system issues. Always consider the complete cooling system before replacing parts randomly.