A sweet, maple syrup-like smell from your 2022 Toyota Highlander is the telltale sign of leaking engine coolant. Ethylene glycol-based antifreeze has a distinctively sweet odor, and when it escapes and contacts hot engine components, this smell becomes very noticeable.
Why Coolant Smells Sweet
The primary component of most automotive coolant, ethylene glycol, has an inherently sweet smell and taste (though it's highly toxic if ingested). When coolant leaks onto hot surfaces and vaporizes, this sweet maple syrup-like odor wafts through the engine bay and often into the cabin through the ventilation system.
Common Highlander Coolant Leak Sources
The Highlander's engines can develop coolant leaks at water pump weep holes indicating seal failure, radiator hose connections and the radiator itself, thermostat housing gaskets, heater hose connections and the heater core, and reservoir tank cracks or cap failures. The V6 and four-cylinder engines each have specific common leak points.
Heater Core Consideration
If the sweet smell is specifically inside the cabin and especially strong when using the heater, the heater core may be leaking. This interior heat exchanger is located inside the dashboard, and leaks release coolant vapor directly into the passenger compartment. Foggy windshield and damp passenger floor are additional heater core leak signs.
Diagnostic Approach
Check coolant level when the engine is cold - low level confirms loss. Look for wet spots or residue around common leak areas. Pressure test the cooling system to reveal the leak location. Check the oil for milky appearance suggesting internal leak. Use UV dye if the external leak is difficult to locate.
Why Prompt Repair Matters
Coolant leaks can escalate quickly. Low coolant causes overheating that can warp cylinder heads, damage head gaskets, and destroy engines. A small leak today can become a breakdown tomorrow. Additionally, coolant is toxic to pets and wildlife attracted to its sweet smell.