What are the reasons for slow engine coolant temperature rise?
3 Answers
The reasons for slow engine coolant temperature rise are: 1. Damaged thermostat causing it to remain open; 2. Faulty cooling fan running continuously. The reasons for high engine coolant temperature are: 1. Insufficient antifreeze in the engine cooling system; 2. Faulty thermostat in the engine cooling system causing overheating; 3. Malfunctioning cooling fan in the engine cooling system, resulting in poor coolant heat dissipation; 4. Faulty water pump in the engine cooling system, causing poor coolant circulation. Precautions for high engine coolant temperature include: 1. Slow down and pull over when driving, but don't immediately turn off the engine; 2. Never pour cold water on the engine when cooling it down.
My car had an issue last winter where the coolant temperature rose very slowly. Even after driving for a long time, the temperature gauge wouldn’t climb. After checking, I found out the thermostat was stuck in the open position. That thing is supposed to stay closed during a cold start, allowing the coolant to circulate only in the small loop for faster warm-up. But when it got stuck, the coolant flowed directly into the radiator circuit, causing heat to dissipate too quickly and preventing the temperature from rising. Other possible causes include insufficient coolant or trapped air bubbles, which hinder heat transfer. A worn-out water pump slowing down circulation can also delay warm-up. If the fan control malfunctions and kicks in when the engine is cold, it draws away heat, making it even harder to warm up. Environmental temperature plays a big role—starting in sub-zero conditions naturally takes longer, but abnormalities should raise red flags. After replacing the thermostat at the repair shop, the improvement was immediate—the temperature normalized much faster. Low coolant temperature not only affects the heating system (making warm air slow to come out) but also increases fuel consumption and wear risks since the engine runs below optimal temperature. I recommend getting it checked by a professional shop early—don’t wait for a small issue to turn into a big problem.
When driving long distances, my engine temperature often rises very slowly, and I found it's due to multiple overlapping factors. The core issue is a faulty thermostat stuck in the open position, causing coolant to prematurely circulate through the radiator. Leaks or air pockets trapped in the cooling system also reduce heating efficiency. Additionally, oil with too low viscosity dissipates heat faster, and driving at low speeds like in city traffic accumulates heat slowly. If the fan control sensor falsely reports high temperature and commands the fan to start prematurely, it also removes heat. During cold spells, the car heats up even harder, but if the temperature is abnormal even in normal conditions, it needs checking. When dealing with it, I first check the coolant reservoir level and whether the fan is acting up, but ultimately leave it to the shop with diagnostic tools for accuracy. Prolonged low engine temperature leads to poor fuel efficiency and may even damage the cylinder head gasket. Timely repairs save hassle and money.
