On the XA50 RAV4 the thermostat lives in the water inlet housing low on the front of the A25A engine block, right where the lower radiator hose lands. That means no intake removal and no fighting with the timing cover - you drop the engine under cover, drain the radiator, pull one hose and two 10 mm nuts. The parts cost is small; the time goes into draining, refilling and getting the air out.
The two things people get wrong are orientation and coolant. The thermostat has a small jiggle valve pin that must point up, and this engine is fussy about trapped air, so if you skip a proper bleed you will chase phantom overheating or a cold heater. Use Toyota pink Super Long Life coolant, pre-mixed, not a generic universal jug.
| Item | Type | |
|---|---|---|
| Floor jack 2 ton minimum Lift the front of the car to reach the under cover and water inlet. | Required | shop |
| Jack stands 2 ton pair, pinch-weld pads Support the car at the factory front jack points while you work underneath. | Safety | shop |
| Wheel chocks Block the rear wheels before lifting. | Safety | shop |
| Socket set 10 mm and 12 mm, 6-point, 3/8 in drive 10 mm for the under cover bolts and the two thermostat housing nuts; 12 mm for a few under-tray/splash shield fasteners. | Required | shop |
| Ratchet and extensions 3/8 in drive, 3 in and 6 in extensions Reach the water inlet nuts past the subframe and hose. | Required | shop |
| Trim clip / panel removal tool Plastic push-pin remover The engine under cover uses plastic push clips as well as bolts. | Required | shop |
| Hose clamp pliers Swivel-jaw spring hose clamp pliers, cable type preferred The lower radiator hose uses a factory spring clamp in a tight spot. | Required | shop |
| Drain pan 8 quart / 2 gallon low profile Catch coolant from the radiator drain cock. | Required | shop |
| Pliers, needle nose Twist a stuck hose loose and handle the drain cock. | Recommended | shop |
| Gasket scraper / plastic pick Plastic or nylon Clean the aluminum housing sealing face without gouging it. | Recommended | shop |
| Shop rags and brake cleaner Wipe the sealing surface and clean up coolant spill. | Consumables | shop |
| Torque wrench 1/4 or 3/8 in drive, 20-200 in-lb range The two housing nuts thread into an aluminum block and are low torque. | Required | shop |
| Thermostat with gasket Toyota 90916-03153 (or equivalent) with rubber seal ring, 80-84 C opening The replacement unit; always fit the new rubber ring, never reuse the old one. | Parts | shop |
| Toyota Super Long Life Coolant Pink SLLC, pre-mixed 50/50; approx 6-7 qt gas, more on hybrid Refill; Toyota pink P-SLLC is the correct spec for this engine. | Consumables | shop |
| Spill-free funnel Universal no-spill radiator funnel with Toyota adapter Lets trapped air burp out of the system while the engine warms up. | Recommended | shop |
| Vacuum coolant fill tool Air-powered vacuum refill kit, needs compressor Best way to avoid air pockets on this engine, especially on hybrids with the heater and inverter loops. | Recommended | shop |
| Nitrile gloves and eye protection Coolant is an irritant and the drain point is directly overhead of you. | Safety | shop |
| OBD2 scan tool Live data capable (coolant temp PID) Confirm coolant temperature rises and stabilizes normally and clear any P0128 stored code. | Recommended | shop |
| Coolant sealed jug Store drained coolant for proper disposal; do not leave it where pets can reach it. | Consumables | shop |
Tool sizes are identical between the 2.5L A25A-FKS gas and the A25A-FXS hybrid: 10 mm under cover bolts and 10 mm thermostat housing nuts on both. The only practical difference is coolant volume and bleeding - the hybrid system holds noticeably more fluid and has separate inverter/heater loops, so allow extra coolant and more heat cycles to fully purge air.
| Water inlet (thermostat housing) nuts, 10 mm | verify in the service manual (low torque into aluminum, roughly 7-9 Nm / 60-80 in-lb) |
| Radiator drain cock | Hand tight only - plastic, do not use a tool |
| Engine under cover bolts | verify in the service manual (snug, approx 8 Nm) |
| Wheel lug nuts (if a wheel is removed) | 103 ft-lb (140 Nm) |
The 10 mm hardware, spring-clamp lower hose and water-inlet location are consistent across the XA50 A25A engines including the hybrid; the exact thermostat housing nut torque and under cover bolt torque should be confirmed against the Toyota service manual before final tightening.
It is in the water inlet housing on the lower front/left side of the engine block, at the end of the lower radiator hose. You reach it from underneath after removing the engine under cover - no need to remove the intake or alternator.
Plan on about 1.5 to 2 gallons of pre-mixed Toyota pink SLLC. A radiator drain only pulls roughly half the system capacity, so you will not replace everything unless you flush, but buy extra for topping up over the following week.
No. Opening the radiator drain cock lowers the level below the water inlet, which is enough. Expect maybe a cup or two of spill when you pull the lower hose, so keep the pan under it.
Almost always trapped air or the wrong-temperature thermostat. Rebleed with the heater on full hot through two full fan cycles, confirm the jiggle valve was installed facing up, and verify the unit is the 80-84 C OE-spec part rather than a colder aftermarket one.