Thermostat Replacement on a Nissan Quest V6
Having Problems with your Thermostat?
The Nissan Quest is an excellent vehicle. I have owned several of these and have had really great service out of them. There are a few issues with these vehicles. One of which I would like to go over today is the replacement of the thermostat. The thermostat can go bad for any number of reasons and manifests its failure in several different ways. If you are undertaking this procedure, I trust that you have diagnosed the thermostat as faulty.
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 note and jot them down or take some pics. Remove the radiator cap.
Removing 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 can be done.
You will need a few tools. I used 90 degree pliers, 3/8 ratchet and short extension, 12mm deep and shallow sockets, 12mm combination (box/open) wrench, flat head screwdriver.
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 (12mm 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.
Making Progress now...
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 separate from the housing.
It goes faster from this point on.
Clean all mating surfaces thoroughly, 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 over done. 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 prior to removal. Make sure that tightness is the same for all bolts to avoid warpage and be careful not to over-tighten, because a broken bolt will turn this in to a big repair.
Now re-install the hoses that you removed, and fill the radiator with the proper 50/50 mix of coolant.
It's not over yet... 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 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 cooing 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), 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 vehice, 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 vehilce is COLD, carfully 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 safety first and proctect 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 confident that air is out of the system and the coolant level stabilzes, check for leaks, and test drive the vehicle 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 short-cuts.