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Thermostat Replacement on a Nissan Quest V6

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I have owned several Nissan Quests. In general, I've had really great service from them.

It's not difficult to replace a faulty thermostat - just don't take any shortcuts.

It's not difficult to replace a faulty thermostat - just don't take any shortcuts.

Having Problems With Your Thermostat?

The Nissan Quest is an excellent vehicle. I have owned several of them, and in general, I've had really great service from them. There are a few issues with these vehicles, though, one of which I would like to go over today: the replacement of the thermostat. The thermostat can go bad for any number of reasons, and it manifests its failure in several different ways. If you are undertaking this procedure, I trust that you have diagnosed the thermostat as faulty.


Step 1: Get Set Up

Start this repair with the vehicle cold. Remove the negative battery cable. You will lose radio presets and other vehicle memory settings, so if these are important, take notes and jot them down or take some pics. Remove the radiator cap.

This photo shows the top radiator hose in the foreground and is taken from the passenger side of the vehicle looking over the fender.

This photo shows the top radiator hose in the foreground and is taken from the passenger side of the vehicle looking over the fender.

Step 2: Remove the Thermostat

The thermostat is on the passenger side of the engine, in a housing that is below the top radiator hose housing. It is difficult to see and even harder to get to, but it can be done.

You will need a few tools. I used 90-degree pliers, 3/8 ratchet and short extension, 12 mm deep and shallow sockets, 12 mm combination (box/open) wrench, and a flat-head screwdriver.

Close-up pic of the housing on the vehicle.

Close-up pic of the housing on the vehicle.

Drain the coolant from the radiator and catch it for re-use or proper disposal.

Remove the top radiator hose for access.

Remove the hose from the thermostat housing and take out the four bolts (12 mm heads) that hold the housing to the engine. This is where things slow down a bit and patience is required.

After the four bolts are removed, the housing should pop off. Be careful to pry on a suitable surface, not to bend any pulleys or crack the aluminum housing, if additional force is used.

Step 3: The Heart of the Matter

With the housing off, it can be removed with the mating surface down and the hose opening facing the rear of the vehicle. This is tricky and took several moments to achieve, but can be done. The thermostat will likely remain in the engine and can easily be removed separately from the housing.

It goes faster from this point on.

Clean all mating surfaces thoroughly, and be careful not to gouge or score the aluminum.

Insert the thermostat in the engine with the top of the thermostat facing out and the "jiggle valve" at the 12 o'clock position. The jiggle valve allows any air trapped in the system to bleed through and is vital to the success of this repair, so don't mess this part up!

Apply a conservative amount of the proper silicone-based RVT sealer to the thermostat housing. I use ultra-grey high temp. Make sure the surface is covered but not overdone. Gently work the housing in the same way it came out, being careful not to rub off the sealant. Fit the housing over the thermostat and install each of the four bolts, starting by hand and tighten to the tension they were at prior to removal. Make sure that the tightness is the same for all bolts to avoid warpage, and be careful not to over-tighten because a broken bolt will turn this into a big repair.

Now reinstall the hoses that you removed, and fill the radiator with the proper 50/50 mix of coolant.

Re-assembled view from the front of the vehicle.

Re-assembled view from the front of the vehicle.

Step 4: Air Removal

This is the last step in the repair, but if you don't do this right the whole repair is at risk.

Bleeding the air out of the cooling system is very difficult on these vehicles. These are the steps that I follow, and I have always had good success finishing the repair this way.

Re-connect the negative battery cable.

Set the heater to "hot" and turn on the blower full speed, start the engine and let run at idle.

Stand by and add coolant (50/50 mix) slowly as the level goes down in the radiator.

The vehicle should slowly reach operating temperature and the heater should become warm.

I elevate the vehicle's front with jack-stands, a lift, or by parking on a sharp slope. The idea is to make the mouth of the radiator the highest point of the cooling system (then air can bubble out as the vehicle warms up). Once you think all of the air is out of the system (it probably isn't), put the cap on (I suggest a new cap), and let the vehicle run until the cooling fan cycles on and off one time. Of course, watch the temp gauge and if the temp rises above normal, stop the vehicle, let it cool and start the air removal process over again.

Once the fan cycles, ensure that the coolant reservoir is full and turn the vehicle off. Let the vehicle get completely cold (it may take hours depending on ambient temperature).

Next, when the vehicle is COLD, carefully remove the radiator cap with a rag over the cap. There should be no pressure on the system if the vehicle is cold, but practice a safety-first approach and protect yourself properly. Repeat the above process, refilling and running the vehicle and allowing it to cool completely at each stage. The air will slowly purge out of the system.

I would go through this process at least three times. Once you are confident that the air is out of the system and the coolant level stabilizes, check for leaks, and test drive the vehicle at varying speeds for several miles.

Wrapping It Up

I hope this has been helpful. I have done this repair many times, and the secret to success for me has been not taking any shortcuts.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.