The Nissan Quest hit the market in 1993 in a joint venture between Mercury and Nissan -- the Mercury Villager is its near-identical twin. In 2004, the Quest entered its third generation and parted ways with its Mercury teammate to become its own, unique minivan. I had to replace the thermostat in my 2004 Quest and found this process to work well.
I started off by positioning the floor jack under one side of the subframe, then lifting that side and sliding a jack stand under the pinch weld just behind the front wheel. I did the same to lift the other side of the Quest.
To drain the coolant, I had to remove the bolts securing the plastic cover to the underside of the engine, using a ratchet and socket, then pull the plastic cover from the vehicle. The drain cock on my 2004 Quest was a plastic, Phillips screw on the passenger side of the radiator. Once the coolant finished draining, I tightened the drain cock to 87 inch pounds.
I found the thermostat housing on my Quest's 3.5-liter engine on the passenger side of the engine block, about a quarter of the way down the block -- just above the alternator. To access it, I had to first remove the Intelligent Power Distribution Module and the automatic transmission cooler line from above it.
Once I gained access to the thermostat housing assembly -- the thermostat and housing are one assembly -- I released the hose clamp securing the coolant hose to it, using slip-joint pliers, and pulled the hose from the assembly. The assembly has just three bolts securing it and I removed the gasket after I pulled the thermostat assembly housing from the engine.
To get the best seal and avoid damaging the thermostat housing assembly, I tightened its bolts to 87 inch-pounds. I connected the hose back into the thermostat housing assembly and slid the clamp to the end of the hose.
Refill the cooling system with Genuine Nissan Long Life Anti-Freeze Coolant and clean water mixed at a 50-50 ratio, and burp the cooling system.
