Why does my temperature gauge climb on mountain passes?

Climbing at highway speed takes a lot of power, and power makes heat. On flat ground the cooling system has room to spare. On a pass, the climb goes on for kilometres, and that spare room gets used up. The BC Ministry of Transportation lists the Salmo to Creston stretch of Highway 3 among the longest grades in the province.

Summer adds to it. Hot air cools the radiator less, and the air conditioning adds load. A trailer or a loaded roof box adds more. A healthy system copes with all of that. A system with low coolant, a sticking thermostat, a weak water pump or a radiator plugged with bugs and road grime falls behind.

Know where your needle normally sits. On most cars it settles near the middle and stays there. If it creeps up on a climb, slow down and switch off the air conditioning. The ministry's advice for long hills is to reduce your speed to avoid overheating.

If it keeps climbing toward H, or a high temperature warning appears, pull over somewhere safe and turn on your hazards. Turn off the accessories. If steam is coming from under the hood, shut the engine off and keep the hood closed until the steam stops. Then follow the overheating steps in your owner's manual, because they vary from car to car.

Sometimes, with care. Once the engine is cool, check the coolant tank. If the level is low, top it up to the full mark with the coolant your manual calls for. Water will do in an emergency, and the system should be flushed and refilled properly soon after. Restart and watch the gauge. If it climbs again, stop and call for a tow.

Driving on with the gauge at H can damage the engine, and Honda's manuals say so directly. A warped cylinder head or a failed head gasket costs far more than a tow off the pass.

The way down needs care too. The ministry advises gearing down on long descents and letting the engine slow you. Riding the brakes the whole way down can overheat them, which our guide to grinding brakes covers.

We start with a pressure test. It brings the cooling system up to working pressure and shows leaks that may only appear when the system is hot. We check the coolant strength, the fan, the thermostat, the hoses and the radiator. Then we call you with photos and a number before anything is replaced.

A cooling system service starts from $165 and includes a pressure test, a flush, and the correct coolant for your engine. If a hose is the cause, the fix is small. If it is a head gasket, you will want to know before the next trip over the pass. The temperature gauge line on our symptom estimator shows the starting price, and you can book a bay for a cooling check before your summer driving starts.