The situation when a car suddenly refuses to start from the starter is familiar to many drivers. A dead battery, a faulty solenoid relay, or wiring problems can catch you by surprise at the most inopportune moment. At such moments, a method that has been proven for decades often comes to mind - “lighting” the car from a tow or starting the engine by pushing.
However, modern cars are significantly different from the equipment produced 20–30 years ago. Complex electronic control systems, automatic transmissions and environmental regulations dictate new operating rules. The answer to the question whether it is permissible to start the engine using a tugboat is no longer unambiguous and now requires a detailed analysis of the technical nuances.
In this article, we will look at the physical principles of starting a motor “from a pushrod”, assess the risks for expensive transmission components and analyze the legal aspects of using a cable on public roads. Understanding these processes will help you avoid costly repairs and potential accidents.
Physics of the process: how launching from a pusher works
The principle of starting an internal combustion engine using an external force is quite simple. The driver's push or the pull of the towing vehicle is transmitted through the wheels to transmission, and then the rotation is transmitted to the engine crankshaft. When the crankshaft rotation speed reaches a certain value, the ignition system generates a spark and the injectors supply fuel, which leads to ignition of the mixture and the engine’s independent operation.
To implement this process, a rigid mechanical connection between the wheels and the engine is necessary. That is why the method is effective on cars with manual transmission (manual transmission). The driver depresses the clutch, accelerates the car, then smoothly releases the pedal, transferring the inertial torque to the engine's starting speed. At this moment, the ignition key must be turned to the ignition switch position.
⚠️ Attention: An attempt to start the engine from a pusher on a car where the pistons are filled with oil or fuel (water hammer) can lead to catastrophic failure - failure of the connecting rods and cylinder block due to the inability to compress the fluid.
The key success factor is crankshaft speed. If the car does not accelerate quickly enough, a spark may jump but no ignition will occur, or the engine may stall immediately after the clutch is released. Modern engine management systems (ECU) also require a minimum voltage in the on-board network for the operation of the fuel pump and injectors, which, with a completely “dead” battery, can become a problem even with a successful crank.
Critical risks for automatic transmissions
Owners of cars with automatic transmission (automatic transmission), variator (CVT) or robotic transmission (DSG, PowerShift), you should forget about the classic method of starting from a tug. The design of automatic transmissions is fundamentally different: the connection between the engine and the wheels is carried out through a torque converter, rather than a rigid clutch. To create the oil pressure necessary to transmit torque and lubricate components, the automatic transmission pump must rotate with the engine running.
When towing or pushing a car with the engine not running and the gear engaged, the wheels rotate the output shaft of the box, but the oil does not circulate in the required volume. This leads to rapid overheating of the clutches and scuffing of the rubbing pairs. Even a short-term attempt to start the engine in this way can damage the expensive unit.
- 🚫 Lack of lubrication: The automatic transmission pump does not create pressure without a running engine, which leads to dry friction.
- 🚫 Hydraulic shock: Sharply shifting into gear while driving can damage the clutch packs.
- 🚫 Electronic blocker: Many modern automatic transmissions physically block switching to neutral when the battery is discharged.
There are rare exceptions for some older automatic transmission models, where the manufacturer allowed towing short distances and at low speeds, but starting the engine with their help absolutely not recommended. The electronics of such boxes simply will not allow you to turn on the gear without voltage in the network.
The myth about neutral transmission in automatic transmissions
Some drivers believe that if you turn on Neutral (N) on the automatic transmission and accelerate the car, and then turn on Drive (D), the car will move. In practice, without a running engine and oil pressure, switching to D while driving is either impossible (electronic locking) or will lead to impact and destruction of the mechanical part of the box.
Mechanical vs Robot: is there a difference?
If everything is relatively clear with classical mechanics, then robotic gearboxes (Robotic Gearbox) occupy an intermediate position. Structurally, they are often mechanics with servo drives. Theoretically, if the design allows you to forcefully engage the gear (sometimes this requires disassembling the gearbox housing or having access to special levers), starting from a pusher is possible.
However, in practice, most modern “robots” (for example, Easytronic from Opel or earlier versions SMG from BMW) require electricity to control the clutch actuators and gear selection. Without a charged battery, you simply won't be able to shift into gear to rev the engine. Even if the gear is engaged, the electronics can block the flow of fuel or spark by reading the lack of signal from the sensors.
For owners robotic transmissions with one clutch (often budget models), the risk is less than with an automatic transmission, but it is still present. Mechanical parts can withstand the load, but electronic control units can malfunction or be damaged due to power surges when the engine is jerked.
Effect on timing chain and piston group
Starting the engine from a tug creates an uneven load on the gas distribution mechanism components. The starter spins the crankshaft smoothly, with increasing force, ensuring uniform tension on the chain or belt timing belt. When starting from a pusher, the jerk can be sharp and impulsive. This is especially dangerous for chain driven engines where the chain already has some wear.
A sharp jerk can cause the chain to jump onto a tooth or even break it. In engines with the so-called “back-to-back” piston design, this is guaranteed to lead to the valves meeting the pistons, which will require a major overhaul of the cylinder head. The cost of such repairs can be several times higher than the cost of a new battery or calling a tow truck.
| Engine type | Risk when starting from a pusher | Likely consequences | Recommendation |
|---|---|---|---|
| Gasoline, timing belt | Medium | Shear of belt teeth, phase failure | Acceptable with caution |
| Gasoline, timing chain | High | Chain jump, break | Not recommended |
| Diesel (any) | Very tall | Damage to connecting rods due to high compression | Strictly prohibited |
| Rotary engine | Critical | Rotor jam | Prohibited |
The method is particularly dangerous for diesel engines. Due to the high compression ratio, it is extremely difficult to spin a diesel engine to the required speed using the wheels. An attempt to do this creates a colossal shock load on the crank mechanism. Often the result is bent connecting rods or broken pistons.
For modern engines with a timing chain drive and a high compression ratio (especially diesels), starting from a tug carries the risk of a major overhaul that exceeds the cost of evacuation.
Legal aspects of towing with a flexible hitch
If the technical ability to start the engine from a tug is in question, then the legal side of the issue is regulated Traffic rules (traffic rules). According to clause 20.4 of the Russian Traffic Regulations, towing with a flexible hitch must be carried out with a driver at the wheel of the towed vehicle. This means that simply tying a car to a cable and yanking it to start without a driver inside is a violation.
In addition, there are speed and distance restrictions. When towing with a flexible hitch, the speed should not exceed 50 km/h, and the distance between vehicles should be from 4 to 6 meters. Must be installed on the cable warning flags or signs indicating towing. Ignoring these requirements can lead to fines and an emergency situation.
- 🚗 Availability of licenses: Only a driver with a license of the appropriate category can drive a towed car.
- 🚗 Brake condition: Towing is prohibited if the steering or braking system is not working.
- 🚗 Lighting devices: At night, the side lights on the towed vehicle should be on (which is impossible if the battery is dead without additional power).
It is important to note that attempting to start the engine in traffic using a cable creates a high risk for other road users. The unpredictable behavior of the vehicle, the risk of cable breakage or sudden stop, make this maneuver risky from a safety point of view.
Instead of risky launching from a tug in traffic, it is better to use a portable booster (launching device). This is a compact lithium-polymer battery that can be carried in the glove compartment and is guaranteed to start the engine without the participation of other cars.
Alternative launch methods and recommendations
Given the technical risks for modern cars and the legal complexities, tow launching is becoming a thing of the past. The safest and most correct method is to use starter-charger (booster) or “lighting” from another car with wires. These methods ensure smooth starting with the starter, without jerking and shock loads on the transmission and timing belt.
If the battery is completely discharged and the starter does not turn, and there is no booster, the only safe option is evacuation to a service station or charging point. Modern cars with systems Start-Stop and complex electronics are especially sensitive to voltage surges and mechanical jerks.
⚠️ Warning: Never attempt to push start a vehicle with a continuously variable transmission (CVT). The design of the variator does not provide for the transmission of torque from the wheels to the engine in such modes, which is guaranteed to lead to the destruction of the belt or chain drive of the variator.
In emergency situations, when you only have a cable and an assistant at hand, and the car has simple mechanics, you can try to start the engine, but only with extreme caution. However, for cars younger than 10-15 years old, equipped with complex injection and environmental systems, this method should be considered highly undesirable.
Frequently asked questions (FAQ)
Is it possible to push-start a machine if the battery is dead?
No, technically this is impossible without special devices. The torque converter does not transmit rotation from the wheels to the engine when the engine is not running, since there is no oil pressure. Attempting to do this will damage the transmission.
What is the minimum speed required to start the engine from a tugboat?
For most 1.5-2.0 liter petrol engines, you need to accelerate the car to 15-20 km/h in second gear. Diesel engines require significantly greater speed and force, which makes the method practically inapplicable.
Is push start dangerous for the catalytic converter?
Yes, in case of unsuccessful starting attempts, unburnt fuel can enter the exhaust system and burn out in the catalyst, causing it to overheat and melt. This is especially true for modern environmental standards Euro-4 and higher.
What is better: towing or cranking?
If the battery has at least some charge, it is better to turn the starter for a long time (with interruptions) than to jerk the car with a cable. The starter is designed for this job, but the transmission and timing belt are not designed for jerky loads.
Can a cable be used to start an electric car?
No, this is absolutely pointless. An electric motor does not require spinning up to start; it requires electricity. The mechanical connection with the wheels in electric vehicles is often broken when the traction is turned off, and pulling a heavy electric vehicle is dangerous for the tow.