The air intake box is the plastic housing that channels outside air into the heater unit, mounted behind the front bulkhead ahead of the driver. It changed specification three times across MGF and MG TF production, producing four catalogued variants. The earliest MGFs (up to VIN WD23991) use one specification. From WD23991 to YD531687, a revised MGF specification was fitted.
From YD531688 onwards (MGF) and continuing through MG TF to 3D612108, a third specification served both the late-era MGF and the early MG TF, this is the longest-running variant and the most commonly replaced. From MG TF VIN 3D612109 onwards, a final specification was introduced. The four variants are not interchangeable because the air intake ducting and fixing points changed with each iteration.
Air Intake Box Fixing Screws and Substitution
Three fixing screw specifications are catalogued to match the box changes: one for pre-WD23991 MGF, one for post-WD23991 MGF through MG TF to 3D612108, and one for MG TF from 3D612109. The catalogue contains a useful backward-compatibility note: if the earliest air intake box (pre-WD23991) is unavailable, the next-specification box can be fitted provided the fixing screws are also upgraded to the matching (four of the post-WD23991) specification. Getting the screws right during any air intake box change avoids cross-thread or loose-fit problems.
Air Intake Duct
The air intake duct connects the air intake box to the heater unit. It is catalogued as a single specification across production, along with its fixing nut and retaining clip (both catalogued individually). Duct deterioration is a common heater complaint on high-mileage cars: a split or disconnected duct allows air to leak into the bulkhead cavity rather than reach the heater unit, producing weak heater airflow despite the blower motor running normally. Inspection and clipping a loose duct into place is often the cure for "weak heater" complaints.
Demister Ducts, Production Change at MGF WD40289
The windscreen demister ducts, which direct heated air to the base of the windscreen, are catalogued as handed pairs in two production variants. MGFs up to VIN WD40289 use the earliest demister duct specification (with a separate ducting elbow catalogued for this era). From MGF VIN WD40290 onwards and throughout MG TF production, a revised demister duct was fitted. A poor seal at the windscreen base of the demister duct, either a split duct or a deteriorated rubber collar, causes warm air to blow into the fascia cavity rather than onto the glass, resulting in a slow or ineffective demist.
This is an MOT concern: insufficient demisting airflow can cause a test failure.
Heater Pipes Assembly and Transmission-Specific Hoses
The coolant-side routing between the engine bay and the heater matrix uses a combination of rigid heater pipes (routed through the underfloor) and flexible hoses at the connection points. The heater pipes assembly is a single specification catalogued with three securing screws. Transmission type determines the hose specification: manual cars use one set of heater return and heater inlet hoses, while automatic cars use a different set plus an additional bypass hose between the bypass circuit and the heater matrix. Three hoses connect the water valve assembly to the heater and to the underfloor pipes: pipe-to-water-valve, water-valve-to-heater, and heater-to-pipe.
Six hose clips secure the connections, catalogued individually. Getting the correct hose set requires knowing whether the car is manual or automatic, ordering the wrong set produces connection points that do not match up.