Driving in prolonged heavy traffic not only causes frustration, missed appointments, lost work, and disputes with partners due to lateness, but also leads to severe engine overheating. This puts extra strain on the radiator and transmission fluid, accelerating their deterioration. So, what can you do to avoid breakdowns on the road? Even some new cars can experience overheating in both the transmission system and radiator temperatures. If any malfunction occurs combined with poor cooling from traffic jams, it can cause wear or overheating severe enough to require towing assistance.
Normally, automatic transmission fluid operates at about 70-90°C (should not exceed 100-110°C), the range where the gearbox runs most smoothly. Under heavy use or in traffic jams, temperatures may rise but should never surpass 120°C, as this accelerates fluid degradation and gearbox damage. Damage is gradual, with heat slowly corroding internal components. Vehicles driven continuously in city traffic, like Sukhumvit, Asoke, Phetchaburi, or construction zones causing congestion, should regularly check transmission fluid levels and change the fluid every 40,000 km. Some older vehicles have aftermarket transmission oil coolers installed to reduce transmission heat. But primarily, changing the transmission fluid as per recommended intervals is essential. For those who drive fast or on mountainous routes where the transmission fluid may be insufficient or undersized, adding a cooler can help reduce operating temperature. This is a relatively low-cost solution, but if there are no issues, routine fluid changes suffice.
Impact of heavy traffic (intensive operation):
Transmission fluid temperature rises above 100°C, causing faster fluid degradation. Heat reduces viscosity and lubrication, leading to slower gear shifts, gear jerks, or burnt odors.
Normal range: 70 - 90°C
Heavy load/High heat: 100 - 120°C (beginning of accelerated fluid degradation)
Critical range: Above 120°C (high risk of gearbox failure)
Frequent temperatures above 120°C can reduce transmission fluid life by up to 70% and shorten gearbox lifespan. Regularly check fluid levels and the cooling system (Oil Cooler).
The cooling system—including radiator, electric fans, water valves, water pump—must work continuously in ambient temperatures over 40°C caused by traffic jams to dissipate engine and transmission heat (especially in systems sharing cooling circuits). Vehicles over 7-10 years old should have their cooling systems inspected regularly to prevent minor issues from escalating into major engine damage.
Warning signs of an overheated transmission include gear jerks when shifting into Drive or Reverse, sluggish acceleration, and a burnt smell when accelerating or changing gears.
Solutions and prevention tips:
Change transmission fluid according to recommended intervals (e.g., every 40,000 km).
Check transmission fluid levels regularly; low levels increase gearbox strain and wear.
Install a transmission cooler to externally dissipate heat from transmission fluid, reducing temperatures to around 70-72°C.
Maintain the radiator system by inspecting radiator fans, cooling fins, belts, water pump, and valves. Replace coolant regularly every 2 years or between 40,000-50,000 km to maintain cooling efficiency and prevent rust and corrosion. Depending on coolant type and vehicle manual, intervals may extend to 5 years or 100,000-250,000 km.
If coolant color changes, rust appears, or sediment builds up, replace coolant immediately without waiting for scheduled intervals.
For heavy use, frequent long-distance driving, or severe traffic conditions, increase coolant replacement frequency.
Use premixed coolant for convenience and optimal performance.
When flushing the cooling system, drain old coolant and clean the system before refilling to prevent clogging.