Checks, in order
- Coolant level over a few daysCheck the reservoir cold, mark the level and recheck after several drives. A steady drop with no drips on the ground points to an internal leak.easy $ · under about $50
- Chemical block testUse a combustion leak test kit on the radiator neck. A color change means exhaust gas is getting into the coolant.easy $ · under about $50
- Cold start misfire codesScan for P0300 or a single cylinder code, often on the rear bank. Misfire on a cold start that clears when warm is a typical pattern.easy $ · under about $50
- Pressure test the cooling systemPressure test with a hand pump and watch for a drop with no external leak. Also look for coolant in the oil on the dipstick.medium $ · under about $50
- RepairThe fix is head gasket replacement and checking the heads for flatness. This is a big job, so get a quote before deciding to repair or replace the truck.hard $$$ · shop-level job, $500+
Applies to: 2003 to 2009 4Runner with the 4.0L 1GR-FE V6 and the 4.7L 2UZ-FE V8, 2WD and 4WD. Engine specific items are labeled, and some issues apply mainly to early model years.
Tools and parts for these checks
Links below are Amazon affiliate links: as an Amazon Associate, toyotadata earns from qualifying purchases, at no extra cost to you. Confirm fitment for your exact truck before you order.
| ITEM | USED FOR | BUY |
|---|---|---|
| Cooling system pressure tester | Finding coolant leaks and testing the radiator cap | Shop on Amazon |
| Toyota Super Long Life Coolant (50/50 premix) | Topping off or refilling with the factory-type coolant | Shop on Amazon |
| Infrared thermometer | Checking radiator, hose and thermostat temperatures | Shop on Amazon |
| Combustion leak (block) test kit | Checking coolant for exhaust gas from a head gasket | Shop on Amazon |
Go deeper
Other engine problems on the 4th Gen 4Runner
More 4th Gen 4Runner problems
- Frame rust or rusted suspension mounts (Frame & Body)
- Clunk, knock or wandering from the front suspension (Steering & Suspension)
- Sticky, melting or cracked dashboard (Body & Electrical)
- Engine overheating or temperature gauge climbing (Cooling)
- Pink or milky transmission fluid, coolant in the transmission (Transmission)
- Turn the key: click or nothing, engine won't crank (Starting & Charging)
All 16 4th Gen 4Runner symptoms in the interactive troubleshooter →
General guidance from owner experience. Confirm torque specs, fluid capacities and procedures in the factory service manual. Brakes, steering and anything structural: if in doubt, have a qualified shop inspect it before driving.