How to overhaul your classic’s heater

Checks and adjustments to transform your heater’s performance

You probably didn’t pay much attention to your car’s heater over the summer. After all, it always produced a hot blast, didn’t it? It didn’t have much to do, though. The colder months see it being force-fed icy air and this – exactly when you need it the most – is when you’ll notice it’s deficient. Heaters get worse over many years as matrix tubes silt up, fins clog with dust, cocks seize and flaps stick. If you have a rose-tinted memory of your heater working better, it’s probably quite accurate.

The need to juggle the controls for demisting or temperature control can expose stiff cables and bad adjustment. Air channelling to the demist or vent nozzles may be vague. Small coolant leaks are evidenced by the formation of greenish scale around the matrix – large leaks are evidenced by perpetual steaming up or wet patches on the carpets.

Happily, all these problems can be solved. You can perform keyhole surgery on your heater and its controls with the unit in situ – but this can be uncomfortable, longwinded and hard on your knuckles. We recommend you bite the bullet, remove it altogether and give it a one-off super-service.

Consult your manual for the finer points of removal. We’ve covered the basics of extracting a heater from under a dashboard. The procedure is usually far simpler if your heater is located in the engine bay.

Don’t be afraid to remove the dashboard. On older classics, where most wires run to the instrument cluster, it’s not a big deal. Removing and replacing the dash provides an opportunity to tighten any fasteners that have worked loose, renew anti-squeak foam between the dash and bulkhead and clean previously inaccessible earths.

Our project car’s heater had a festering mouse’s nest in it – a significant health risk. We discarded the unit. If you have no such option, make sure everything is spotlessly cleaned and disinfected before reassembly.