Have you noticed that the temperature gauge needle creeps into the red zone as soon as you press the gas? Or the dashboard lights up engine overheating icon specifically during overtaking? This problem is familiar to many car owners - the car becomes “feverish” when accelerating, although at idle or in a traffic jam the temperature remains normal. What's the matter?
The reasons for this behavior lie in thermal imbalance motor. During acceleration, the load on the engine increases significantly: the amount of fuel burned increases, friction in the cylinders increases, and the cooling system must cope with peak heat release. If at least one element of this system fails, the temperature creeps up. In this article we will analyze 7 Key Causes of Overheating During Overclocking, including those that are often missed even by experienced mechanics, and we will provide a checklist for self-diagnosis.
1. Faulty thermostat: why the engine “boils” only under load
The thermostat is "manager" of the cooling system, which decides where to direct the antifreeze: in a small circle (for quick warming up) or a large circle (for cooling through the radiator). If it is stuck in the half-open position, the fluid does not circulate intensively enough, and during acceleration heat exchange does not keep up with rising temperatures.
How does this manifest itself:
- 🔥 At idle the temperature is stable, but when the speed increases, the arrow creeps up.
- 🚗 After stopping, the temperature slowly drops (the radiator does not have time to give off heat).
- ❄️ The lower radiator pipe remains cold even on a warm engine.
You can check the thermostat without removing it: warm up the engine to operating temperature (90°C) and touch the upper and lower radiator pipes. If the bottom one is cold, the thermostat does not open completely. B VW Golf IV, Toyota Corolla E12 and Renault Logan first generation this is a common problem due to the poor quality of the original thermostats.
⚠️ Attention: Never remove the expansion tank cap on a hot engine! The pressure in the system can exceed 1.5 atm, and boiling antifreeze will burst out, causing burns.
If the thermostat is stuck in the open position, the engine will take a long time to warm up to operating temperature, and the heater will blow cold air. This is less dangerous for the engine, but increases fuel consumption by 5–10%.
2. Clogged radiator: when air does not flow and antifreeze does not cool
The radiator is “light” cooling systems. If its honeycombs are clogged with dirt, insects or corrosion products, heat transfer is disrupted. When driving at low speed (in a traffic jam), the radiator air flow is weak, but during acceleration the air flow should compensate for this. If the radiator is clogged - cooling efficiency drops by 2–3 times.
Signs of a clogged radiator:
- 🌡️ The temperature rises during acceleration, but returns to normal at idle with the fan on.
- 🕷️ Between the radiator and the air conditioner condenser you can see a “fur coat” of poplar fluff and dirt.
- 💧 The antifreeze in the expansion tank is cloudy, with rust particles.
There are two ways to clean the radiator:
- External washing: a stream of water under a pressure of 2-3 atm (no more, so as not to bend the honeycombs!). Use special cleaners, e.g. LIQUI MOLY Kuhler-Reiniger.
- Flushing the system: fill in flushing fluid (e.g. LAVR Radiator Flush Classic) for 10–15 minutes, then drain and rinse with distilled water.
How to check a radiator for blockages without removing it?
Start the engine, turn the heater on to maximum and let it run for 5-7 minutes. If barely warm air comes out of the deflectors, and the radiator pipes are hot, the problem is clogged honeycombs or a faulty heater tap.
| Type of blockage | Reason | Solution |
|---|---|---|
| External (dust, fluff, insects) | Driving on dusty roads, rarely washing | Pressure wash + cleaner |
| Internal (rust, scale) | Using water instead of antifreeze, old antifreeze | Washing with special chemicals (for example, Hi-Gear Radiator Flush) |
| Oil deposits | Oil getting into antifreeze (cylinder head gasket is broken) | Radiator replacement + cylinder head repair |
3. Faulty cooling fan: when there is not enough airflow
The fan turns on when natural airflow to the radiator is insufficient (in traffic jams or at low speed). But if it does not work or rotates too slowly, when accelerating air flow does not compensate for temperature rise. This is especially noticeable on machines with electric fans (for example, Ford Focus 2, Kia Rio 3).
Causes of fan malfunction:
- 🔌 The fuse has blown (check
F27orF30in the fuse box). - 🤖 The relay or temperature sensor has failed (on VAZ 2110–2112 this is a common problem).
- 🔋 The electric motor brushes are worn out (the fan spins jerkily or does not gain momentum).
How to check:
- Start the engine and let it warm up to 95–100°C.
- Turn on the air conditioner - the fan should start immediately (on most cars it runs constantly when the AC is on).
- If it doesn’t turn on, check the fuse, then apply 12V directly to the fan connector (it should turn on).
⚠️ Attention: On some vehicles (for example, BMW E60, Audi A4 B6) the fan is controlled by the ECU. If it does not turn on, diagnostics with a scanner is required (for example, Launch CReader) for errors in the control circuit.
4. Problems with the pump: when antifreeze does not circulate
The cooling system pump (pump) provides forced circulation of antifreeze. If it is worn out or jams, when the engine speed increases (that is, during acceleration) pump performance drops, and the liquid stagnates in the “hot” areas (cylinder head, around the combustion chambers).
Symptoms of a faulty pump:
- 🔧 Extraneous noise (grinding, howling) from the timing drive (on Renault Duster and Nissan Almera G15 the pump is driven by a timing belt).
- 💦 Antifreeze is leaking from under the pump pulley (the oil seal is worn out).
- 🌀 On a warm engine, the upper radiator pipe is hot and the lower one is cold (fluid does not circulate).
The pump should be replaced at the first sign of wear. On most modern cars (for example, Hyundai Solaris, Skoda Octavia A5) it is integrated into the timing mechanism, and its resource coincides with the life of the belt - 60–90 thousand km. If the pump fails earlier, check the quality of the antifreeze (aggressive additives corrode the oil seal) and the belt tension.
Check the antifreeze level in the expansion tank|Listen to the noise from the pump on a warm engine|Touch the radiator pipes (should be hot and at the same temperature)|Inspect the pump installation site for antifreeze leaks-->
5. Air lock in the cooling system
The air in the cooling system acts as heat insulator: It blocks the circulation of antifreeze in critical areas (for example, in the cylinder head). When overclocking pressure in the system increases, and the air lock may move, blocking fluid access to the radiator or heater. This is a common problem after replacing antifreeze or repairing the cooling system.
Signs of an airlock:
- 🌬️ The stove blows cold air, although the engine is warmed up.
- 📈 The temperature fluctuates when the speed changes (it’s normal at idle, it increases when accelerating).
- 🔊 Gurgling sounds in the expansion tank.
How to remove a traffic jam:
- Start the engine and let it run for 10-15 minutes with the expansion tank cap open.
- Press on the radiator hoses to “expel” the air (do this with gloves - antifreeze is toxic!).
- If it doesn’t help, lift the front of the car on a jack (so that the radiator becomes the point of the system) and repeat the procedure.
On some cars (for example, Opel Astra H, Chevrolet Lacetti) is provided for bleeding air special fitting on the stove pipe. You need to unscrew it on a warm engine until antifreeze flows out without bubbles.
If, after removing the plug, the temperature continues to rise during acceleration, the problem lies elsewhere - for example, a faulty thermostat or a clogged radiator.
6. Low level or poor quality of antifreeze
Antifreeze not only cools the engine, but also protects the system from corrosion and scale. If its level is below the minimum or the fluid has not been changed for a long time, its heat capacity and lubricating properties deteriorate. During acceleration, when the engine load is maximum, This antifreeze doesn't work with heat removal.
What you should be wary of:
- 📉 The antifreeze level in the tank is below the mark
MIN(check on a cold engine!). - 🔴 The color of the antifreeze has become rusty or cloudy (a sign of corrosion or mixing of incompatible types).
- 🧊 Sediment or flakes are visible on the walls of the tank (decomposition of additives).
What antifreeze to fill:
| Antifreeze type | Color | Service life | Application |
|---|---|---|---|
| G11 (hybrid) | Green, blue | 2–3 years | Old cars (before 2000), VW, Audi, Skoda until 1996 |
| G12 (carboxylate) | Red, pink | 5 years | Most cars after 2000, Toyota, Honda, Hyundai |
| G13 (lobrid) | Yellow, orange | 5–10 years | New cars (after 2010), BMW, Mercedes, Porsche |
Important: Never mix different types of antifreeze! For example, G11 and G12 when mixed, they form a gel that clogs the radiator and pipes. If you need to top up, use distilled water (as a last resort) or the same type of antifreeze.
7. Problems with the ignition system or fuel equipment
It would seem, what does ignition have to do with it? The point is that Late ignition or rich fuel mixture lead to incomplete combustion of fuel and an increase in heat generation in the cylinders. The engine begins to “stupid” during acceleration, and the temperature rises due to:
- 🔥 Detonation (explosive combustion of the mixture instead of smooth combustion).
- 💨 Fuel gets into the exhaust system (it burns out in the manifold, heating it to 800–900°C).
- 🛢️ Clogged injectors (fuel is sprayed unevenly, some burns on the cylinder walls).
How to diagnose:
- 🔧 Check the spark plugs: if they are black and wet, the mixture is too rich.
- 📊 Connect a diagnostic scanner (for example, ELM327) and check for errors on the oxygen sensor (
P0171- lean mixtureP0172- rich). - 🔊 Listen to the engine at idle: if you hear a “ringing” (detonation), you need to adjust the ignition timing.
On carburetor cars (for example, VAZ 2107, GAZ 3110) the problem often lies in incorrect carburetor setting or clogged air filter. On injection (Lada Granta, Kia Ceed) - in faulty sensors (mass air flow sensor, lambda probe) or air leaks through cracks in the manifold.
FAQ: Frequently asked questions about overheating during overclocking
Is it possible to drive if the car only heats up when accelerating?
Short term - possible, but it's not worth the risk. Prolonged overheating (above 110°C) leads to:
- Deformation of the cylinder head (repair will cost 30–50 thousand rubles).
- Burnout of the cylinder head gasket (antifreeze will get into the oil, the engine will start to peddle).
- Seizure on pistons and cylinders (engine overhaul or replacement).
If the problem appears suddenly, drive at low speed (up to 60 km/h) with the heater turned on to maximum to remove some of the heat.
Why does the temperature drop when the stove is turned on?
The stove is additional radiator, which removes heat from antifreeze. When you turn it on to maximum, some of the hot liquid passes through the heater radiator, cools and returns to the system. This is a temporary solution, but it helps you get to the service station without the risk of overheating.
If the temperature drops too much (below 80°C) - check the thermostat: it may be stuck open.
What antifreeze is best to use to avoid overheating?
The choice depends on the material of your car’s cooling system:
- For aluminum radiators and blocks (most modern cars) - G12+ or G13 (for example, Motul Inugel Optimal, CoolStream Premium).
- For copper/brass radiators (old cars) - G11 (for example, Felix Carbox G11, Sintec Lux G11).
Important: Antifreeze must match manufacturer's tolerances. For example, for Volkswagen and Audi this is VW TL 774-D (G12) or VW TL 774-G (G13).
Could overheating during acceleration be related to the transmission?
Yes, but indirectly. If automatic transmission overheats (for example, due to a low oil level or a clogged automatic transmission radiator), its torque converter creates additional load on the engine. As a result:
- Engine speed increases more slowly (the car “stumbles” when accelerating).
- The engine runs longer under load, which leads to overheating.
Check the oil level in the automatic transmission and the condition of its radiator (it is usually located in front of the engine cooling radiator).
Is it worth using additives for the cooling system?
Additives type "Stop-flow" or "Radiator cleaner" - this is temporary solution. They can:
- ✅ Seal small leaks (for 1-2 months).
- ✅ Dissolve light deposits in the radiator.
But!
- ❌ Clog thin channels (for example, in a stove or oil radiator).
- ❌ React with antifreeze, forming flakes.
Use them only for emergency repairsto get to the service station. To fully treat the cooling system, you need to flush and replace the antifreeze.