The standard heater was adequate for its era but falls short of modern expectations on a car used in cold conditions or driven at touring pace on open roads. The original Smiths unit uses a single-speed blower motor with a modest impeller, pushing air through a matrix that was designed for the cabin heating demands of 1962. On a car used year-round in British weather, the difference between the original specification and what is achievable with targeted upgrades is substantial.
Improved Matrices
The high-efficiency heater matrix replaces the standard matrix with an uprated unit that delivers measurably better heat output from the same coolant flow, making a noticeable difference to cabin temperature and windscreen demisting performance. It is a direct replacement for the original matrix and fits within the standard heater box without alteration. Aluminium matrices are a further option, lighter than the original and resistant to the corrosion that affects original brass-and-copper matrices over time.
Airflow & Sealing
The two-speed heater motor and large impeller kit replaces the original single-speed motor with a two-speed unit paired with a larger impeller, increasing airflow through the matrix at both speeds. Both upgrades are available individually or as a combined kit for owners carrying out a full heater overhaul, where fitting both at the same time gives the greatest overall improvement. The heater box seal kit completes the package by restoring the airtight integrity of the heater casing, without which any improvement in matrix performance or airflow is partially lost through the degraded seals.
Heater Valve
Modern replacement heater valves with improved construction and longer service life are available. On the MGB GT V8 the correct operating direction must be retained, as fitting a four-cylinder MGB valve causes the dashboard control to operate backwards. Quality replacement valves match the correct specification and provide improved long-term reliability over tired original units. Various small modernisations are also available, including improved fan motors with better service life and blade-fuse protection for the heater circuit.