How your car heater actually works (no jargon, just the basics)
A heater core
Right, so you fire up your car tidy early on a foggy morning in Hamilton — maybe you’re heading across the Fairfield Bridge or braving all the stop-start at Five Cross Roads. You crank the heater… but it’s just blowing cold. Annoying, eh?
The thing is, your car heater actually piggybacks off the engine. Most modern cars, like those Toyotas, Suzukis, Euros like Peugeot 308s, or even the odd Nissan Leaf, use engine coolant to move heat about. The engine gets hot once you’re cruising up Te Rapa Road or crawling round Chartwell. That coolant, heated by your engine, flows through a little radiator (called the heater core). The heater blower fan then pushes air through that hot core and sends it into your cabin, so you can unfreeze your fingers.
How warm it gets in there depends on a thing called the heater control valve. On some cars (like old-school Mitsis or Subarus), you twist or slide the controls to open this valve up. On others — especially with climate control (think newer Mazdas or BMWs you see in Flagstaff) — it’s all handled automatically.
Learn more about how car heaters work >
Why your heater’s gone cold (and what might be causing it)
Few things are rougher in winter than a heater that just won’t heat. We see this heaps at Grimmer Motors, especially after folks trek in from Cambridge or Ngaruawahia for school drop-off and suddenly realise it’s freezing inside the car.
Low coolant – By far the most common. Could be because of a sneaky leak somewhere — a worn hose, a cracked radiator, or even the heater core itself. Without enough coolant, nothing’s gonna get warm. Watch your temp gauge on the dash, and don’t risk overheating. If there’s a puddle under your car or you’re topping up coolant all the time, it’s time for a visit. Learn more about diagnosing cooling system problems >
Stuck thermostat – If the thermostat’s stuck open (happened just last month on a Honda Jazz from Tamahere), the car never warms up properly, even after a long run along Avalon Drive. Heater blows lukewarm forever. You might also notice the engine running a bit sluggish.
Blower fan on strike – We see this on everything from older Ford Focuses to late-model Honda Civics. Sometimes it’s a dodgy fuse or a tired motor, other times the switch itself cops out. No fan means no warm air blowing in, simple as that.
Blocked heater core – On cars that have seen a few Hamilton winters and not much coolant maintenance (like that classic Volvo a customer brought in from Morrinsville), gunk can build up in the heater core, so not much heat makes it through. Sometimes a good flush will sort it, sometimes you need a new core.
Does a broken heater matter, or can I just tough it out?
A healthy level of coolant
Honestly, if the heater’s not working because of a coolant leak, don’t muck about. That means your engine’s running hot, and if you keep hammering it across town or out towards Raglan, you could end up needing a whole new engine. Here’s what we tell our customers to watch for:
- Temp gauge climbing too high
- Coolant puddles near front wheels or under the engine
- Heater never gets warm (or blows outright cold)
- Coolant tank looks empty (but ONLY check once the engine’s cold!)
Little problems can sneak up on you, especially with all the potholes around Dinsdale or the constant stop-go in Rototuna wearing hoses and joints.
Need your heater sorted? We’re your local Hamilton crew
If you pop into Grimmer Motors — whether you drive a Kia, Audi, Toyota hybrid, or your trusty old Corolla — one of our techs can suss out what’s going on. Doesn’t matter if it’s a leaky core, a tired thermostat, or just something simple like a blown fuse — we’ll get you back on the road (and warm) in no time. Car service Hamilton, WOFs, hybrid repair, you name it, we do it.
If your heater’s playing up, or you reckon you’ve got a coolant leak, save yourself a headache — swing by for a check, or just hit the button below to book in.