Why hot summer days, mountain climbs and thin air push cooling systems on BMWs, Audis, MINIs, Porsches and other imports, the warning signs, what to do if the gauge climbs, and the parts that usually fail.
Denver summers are dry and sunny, and the mountains are right there. That's a great combination for a road trip and a tough one for a cooling system. A 90-degree afternoon, a long climb up a pass with the AC on, and an aging plastic coolant part is how a lot of imports end up on the shoulder.
Why it's harder here
- Thin air. At altitude, there's less air moving through the radiator to carry heat away, and the cooling fans have to work harder.
- Long climbs. Mountain grades keep the engine working hard for a long time, not just for a minute on an on-ramp.
- Lower boiling point. Water boils at a lower temperature up high. A healthy cooling system is pressurized to raise the boiling point, which is why a weak or leaking cap or a small leak matters more here.
- Turbos. Many modern imports are turbocharged, and turbos work harder at altitude to make the same power, which means more heat.
Warning signs
- The temperature gauge moving above where it normally sits
- A coolant warning light or message
- A sweet smell after a drive, or steam from under the hood
- Fans running hard and loud long after you shut the car off
- Pink, green or blue crust around hoses and plastic fittings
- A coolant level that keeps dropping
If it starts to overheat
- Turn the AC off.
- Turn the heater to full hot and the fan to high. It feels terrible in July, but it pulls heat out of the engine.
- Ease off and get out of traffic if you can.
- If it keeps climbing, pull over somewhere safe and shut it off.
- Don't open the radiator or expansion tank cap while it's hot. It's under pressure and can spray scalding coolant.
Driving an overheating engine is how a water pump job turns into a head gasket or a new engine.
The parts that usually fail on imports
Most modern European engines use a lot of plastic in the cooling system, and plastic gets brittle after years of heat cycles. These are the usual suspects, with what owners reported paying:
- BMW N54/N55: electric water pump and thermostat
- VW/Audi 2.0T: water pump and thermostat housing
- Audi 3.0T supercharged V6: water pump and thermostat
- MINI Cooper S: thermostat housing and water pump
- Porsche M96/M97: water pump
- Toyota/Lexus 3.5 V6: water pump
- Subaru EJ25: timing belt and water pump, and head gaskets on non-turbo engines
Before a summer road trip
- Check the coolant level with the engine cold
- Look under the car after it's been parked overnight
- Ask your shop to pressure-test the cooling system if you've been topping off
- Make sure the AC blows cold before you're in the middle of nowhere
- Check tire pressures. Hot pavement and a loaded car add up.
If your AC isn't cold, here's what owners paid for a Honda/Acura AC compressor.
General information, not legal advice. Check CDOT and your owner's manual for the rules and specs that apply to you.