FAW Start The Preheating Device: A Comprehensive Guide to Its 3 Components

Welcome to this comprehensive technical guide on the FAW Start The Preheating Device (Part No. 3750010-81D), a critical component for all-weather reliability in the FAW Jiefang CA4251P66K24T1A3E5 6×4 diesel semi-trailer tractor. This system is essential for cold-weather starting.

The function of the FAW Start The Preheating Device, also known as an “intake grid heater,” is to warm the air entering the engine’s cylinders *before* cranking. This ensures a fast, clean start in cold temperatures, reducing starter wear and unburnt fuel (white smoke).

This in-depth guide is an essential resource for professional technicians and fleet managers. We will deconstruct the entire FAW Start The Preheating Device logic assembly into its 3 smallest serviceable units: the main heater element, the high-current ground wire, and the mounting bolt.

Core Component: The Air Heater Assembly (3750010-81D)

The heart of the FAW Start The Preheating Device is the ‘Air Heater Assembly’ (3750010-81D). This is a “grid heater,” a high-amperage electrical resistance heating element. Unlike “glow plugs” which are inserted into each cylinder, this single, robust unit is mounted in the engine’s intake manifold, between the intercooler and the cylinder head.

This component consists of one or more “calrod” style elements, similar to the element in an electric oven, arranged in a grid. This grid is designed to heat the massive volume of air being drawn into the engine during the “key-on” pre-start phase. The function of this FAW Start The Preheating Device is to raise the intake air temperature significantly, from sub-zero to well above freezing.

The operation is controlled by the engine’s ECU. When the driver turns the key in cold weather, the “wait-to-start” light illuminates. This signals that the ECU has engaged one or more high-current relays, which are sending hundreds of amps from the battery to this FAW Start The Preheating Device. The grid element heats up to a red-hot glow in just a few seconds.

As the starter cranks the engine, the cold outside air is drawn through this red-hot grid, instantly raising its temperature. This heated air is then drawn into the cylinders. This ensures that when the piston compresses the air, it reaches the auto-ignition temperature of diesel fuel easily. Without the FAW Start The Preheating Device, the cold, dense air and the cold, metal engine block would act as a “heat sink,” wicking away the heat of compression and preventing the fuel from igniting, resulting in a “no-start” condition.

The Critical Ground Wire (3724500-73D)

The ‘Air Heater Ground Wire’ (3724500-73D) is the second component of the FAW Start The Preheating Device. This is not a small, simple wire. An intake grid heater can draw 150-200 amps at 24 volts, which is an enormous electrical load (over 4,000 watts).

To handle this massive current, the heater requires a dedicated, heavy-gauge ground cable. This ‘Air Heater Ground Wire’ provides a secure, low-resistance path from the heater element’s ground stud directly to the engine block or chassis ground.

A failure of this single ground wire will render the entire FAW Start The Preheating Device inoperable. If the wire is loose, corroded, or broken, the electrical circuit is incomplete. The “wait-to-start” light may still come on (as the ECU *thinks* it has engaged the relays), but no current will flow, and no heat will be generated. A technician troubleshooting a “no-heat” condition on the FAW Start The Preheating Device should always check this ground wire for continuity and for a clean, tight connection.

The Mounting Fastener (Q1840812)

The final component is the ‘Hex flange bolt, coarse rod (Standard Type)’ (Q1840812). This is the fastener used to secure the ‘Air Heater Ground Wire’ to the engine or chassis.

The “flange” head of this bolt is critical. It acts as an integrated, wide-area washer. When tightened, this flange presses the ground wire’s terminal ring firmly against the bare metal of the chassis, creating a large, secure, low-resistance contact patch. A standard, non-flange bolt would concentrate the pressure on a small area, leading to high resistance and heat, which could melt the wire. This specific bolt is a key part of the FAW Start The Preheating Device‘s electrical integrity.

Why a FAW Start The Preheating Device is Essential for Diesel Engines

Understanding the FAW Start The Preheating Device requires understanding the core principle of a diesel engine: **compression ignition**. Unlike a gasoline engine, a diesel engine has no spark plugs. It operates by compressing air to such an extreme pressure (a 17:1 compression ratio or higher) that the air temperature rises to over 540°C (1,000°F). At this exact moment, fuel is injected, and it spontaneously ignites from the heat of the air alone.

This entire process relies on the air reaching that auto-ignition temperature. On a cold day (e.g., 0°C or 32°F), this becomes extremely difficult. The cold, dense air being drawn in, combined with the “cold soak” of the massive iron engine block, acts as a giant heat sink, wicking away the heat of compression. The air charge may only reach 300°C, which is not hot enough to ignite the fuel.

The result is a “no-start” or “hard-start” condition. The starter will crank the engine, and the injectors will spray fuel, but it will not ignite. This unburnt fuel is then blown out of the exhaust as thick, acrid, **white smoke**. This process is terrible for the engine, as it washes the lubricating oil off the cylinder walls (“cylinder washdown”) and puts an immense strain on the FAW Starter Motor and batteries.

This is where the FAW Start The Preheating Device becomes the solution. By pre-heating the intake air *before* it even enters the cylinder, it gives the compression stroke a massive “head start.” The air that starts at 50°C (instead of 0°C) will easily reach the 540°C auto-ignition point.

This results in:

• **Faster, Cleaner Starts:** The engine fires almost instantly.
• **Reduced White Smoke:** The fuel ignites on the first stroke, rather than being blown out as unburnt vapor.
• **Reduced Starter & Battery Wear:** The engine starts in 2-3 seconds instead of 10-15 seconds of labored cranking.
• **Reduced Engine Wear:** The FAW Start The Preheating Device prevents the cylinder “washdown” that occurs during a cold, wet start.

The FAW Start The Preheating Device may also remain on for a short period *after* the engine starts, operating as a “post-heat” device. This helps the engine run smoothly during its initial warm-up, further reducing emissions and engine “chatter.” This makes the FAW Start The Preheating Device a critical component for both engine health and emissions compliance.

FAW Start The Preheating Device Parts List

The following table provides the complete, detailed breakdown of all 3 components identified in the ‘Start Preheating Device’ diagram for the FAW CA4251P66K24T1A3E5 tractor. The FAW Start The Preheating Device is essential for cold-weather operation.

Technical Specifications and Assembly Context

The specifications for the FAW Start The Preheating Device are defined by its function as a high-wattage intake air heater. The reliability of the FAW Start The Preheating Device is key to all-weather starting.