Overheating seems to be a fairly common issue with the 240sx, often it is the result of a poorly maintained system rather than any flaw in the design or manufacturing. You can use your FSM to troubleshoot and diagnose any problems, there are also illustrated walkthroughs and tq. settings to supplement this (admittedly simple by comparison) writeup. This writeup covers the system removal and replacement in its entirety, how much of this you need is up to you.
Time: 3-5 hours
Cost: $150-$450 (including new radiator)
10mm socket with extensions and open-end wrenches
jack and stands (optional – lowered cars)
pressure checker (optional)
rubber mallet (optional)
large drain pan
upper and lower radiator hoses
6.7 liters or 7-1/8 qt of pre-diluted coolant
a few gallon jugs of distilled water (not drinking or spring water)
Prior to performing any service on the coolant system, consult the FSM to try and pinpoint your problems. This could save you time and money better spent!
Begin by parking your car on level ground. Chock your wheels if you plan on leaving the car on the ground, or jack and secure your stands if you need more clearance. Disconnect the ground cable from the negative terminal on the battery. Make sure the car has cooled down sufficiently before attempting to proceed.
Look at the back of the radiator on the bottom driver’s side. You should see your drain plug in all of its plastic glory.
Position your drain pan under this area and push your climate controls over to full heat. Remove your radiator cap. Remove the drain plug and allow all of the fluid to drain completely. When its dry, locate the drain plug on your block and scoot the pan under it, then repeat the process.
Now you can access all of your coolant-related parts without making a huge mess.
Blown-up diagram of coolant system for reference:
The first step in the process is removing the fan shrouds. There are three large pieces to be primarily concerned with, along with the tabs and screws and bolts that hold them all in place. Begin by pulling all of the vacuum lines routed over the top part of the shroud and pushing them out of the way (you can disconnect them, but its not necessary).
Next, remove the clips holding the upper portion of the shroud to the radiator, and pulling the shroud clear of the bay. Be careful not to misplace any screws of clips and note where they belong. if something breaks, don’t fret; a ziptie will literally replace any of the pieces used to secure the shroud to the radiator when you’re ready to replace it.
You should now have access to the lower portions of the shroud, and removing them is as easy as the top was.
Now that you have some more room to work with, it’s time to decide where to begin the actual work. Logically, the more room you have to work in the engine bay the better. Removing the radiator hoses will be the best way to start. Using the flathead screwdriver, loosen the hose clamps at the ends and wiggle/twist the hose as you pull it from its respective connector for best results. This may be difficult if you’re a weenie, your dad should be strong enough to help you out.
This is an excellent time to inspect your hoses for bulges, cracks or other punctures causing whatever problems you may be having. Inspect carefully and discard them if they are trashed. You can retain your hose clamps if they look to be in good condition, but they’re cheaply bought at the store.
Pull the hose leading from your radiator filler neck to the overflow tank and inspect it. I actually had a problem with losing coolant and i could not figure out where the leak was; turns out this hose had been hit by the fan somehow and i replaced most of the rest of my system before finding it!
With your hoses out of the way, check the fan clutch for proper operation by spinning it manually. It shouldn’t quite spin freely but it should be able to turn a few times before slowing and stopping. Further inspection can be performed once it is removed.
You CAN remove the plastic fan first if you choose, but if you’re dexterous enough you can do without. Use your open-end 10mm wrench to remove the bolts holding the assembly onto the front of the block, and give it a slight tap to break the old gasket’s seal. Some coolant could leak out, so it’s a good idea to keep your pan under the front of the block.
Check for rust and check the movement of the vanes while you have the pump in your hands. The FSM provides more detailed info regarding inspection. Set the pump and fan assembly aside.
Look where you removed the upper radiator hose from the intake manifold, and you will spot the coolant inlet elbow. Sandwiched between that and the manifold is the thermostat. Use your 10mm socket and extension with a wrench to remove the three bolts and pull it loose from its gasket seal. More coolant may drain from this when its pulled, and the thermostat should be visible.
You can check and retain the thermostat if you choose, but they are a cheap buy at the Nissan dealership and you can even buy a Nismo version that opens a few degrees cooler for enhanced performance.
The last and probably the most common place a 240sx coolant system can fail is the overflow reservoir. It is very common for the plastic to become brittle and crack, and once that happens it’s only a matter of time before you will be leaking from this location. I have seen all sorts of repair jobs ranging from plastic patches and tape to complete replacements with items as varied as plastic bottles and jugs. The reason for this is that these containers, for how simple they are, are expensive to replace with an oem part, and it is difficult to find a used replacement in good condition. There are aftermarket solutions available ranging from a $5 generic from O’Checker’s PepZone to all-metal “racing” applications if your pockets are deep. They all install in a similar manner and perform the same function to varying degrees of durability and accuracy.
Remove the 10mm bolts holding the overflow reservoir to the engine bay and flush it to remove any sediment buildup from your system that collected in it.
The last part to be concerned with is the radiator itself. It is held in place by rubber bushings that can be removed by pulling the 10mm bolts holding the tabs to the radiator support. After pulling them off and setting them aside, pull back and up on the radiator to lift it out of its place. *NOTE* if you have an automatic transmission, you will have to remove the transmission fluid cooler lines from the bottom of the radiator before pulling it out.
If you are installing a new radiator, grab the rubber bushings from the old unit, you will more than likely need them.
Installation of the parts is basically the reverse of the removal process in most cases. Start with the water pump and fan clutch. At this point it is much easier to install without the plastic fan in the way, so if you haven’t already, remove it with your 10mm wrench. Make sure that the mating surfaces of the block and pump are clean of all of the old gasket material, a Scotch-Brite pad can help with anything that a toothpick or plastic knife leaves behind. Apply a thin bead of liquid gasket around the outside of the pump. Avoid using too much, and keep it in the groove or outside as much as you can, including around the bolt holes. *TIP* If you wear latex surgical gloves, you can easily clean up or spread out any mistakes.
With the pump/fan clutch in hand, put a few of the bolts in their holes evenly spaced around the unit, and place it against the block. Be mindful that you don’t want to move it around much as the gasket will smear or find its way into the pump. Finger tighten the bolts to hold the pump in place and proceed to tighten them in sequence while adding the ones you have left. Torque them to proper specs per the FSM.
While you have your liquid gasket handy, its a good time to replace the thermostat and elbow. MAKE SURE THE THERMOSTAT IS FACING THE CORRECT DIRECTION WHEN INSTALLING! Make your gasket and use the bolts to install the elbow over the thermostat.
While you wait the proper 20-30 minutes for the silicone to set, you can transfer your bushings to your new radiator and install it, or re-install the old radiator. Some members flush their radiators with hose water prior to re-installation, the merits and disadvantages of doing this are up for debate. Since you will be flushing the entire system later, I would skip it.
With the pump and fan clutch now installed and sealed, re-install your fan. Next is the shroud, if you lost or broke any of the clips or screws, you can use zipties to secure everything together. Make sure the parts fit well and have very little movement if any.
Now on to the hoses. Place your clamps over the hoses prior to installing them and insure that their location and rotation on the hose will ensure easy access to it. Doing the lower hose first was easier for me, you will be pushing from underneath the car to fit it over the opening in the radiator and the coolant outlet on the block. Tighten appropriately and do the same for the upper hose, installing the motor side first, then the radiator.
Now install your overflow reservoir and attach the hose to the radiator filler neck.
Make sure that your drain plugs are in place and the hoses are tight, then fill the radiator with distilled water. Now is a good time to start looking for leaks.
With your heater set to full, start your car and let it warm up to operating temperature (watch for leaks while its running!), then shut it off and let it cool down. Drain the water and repeat this process as many times as you deem necessary to flush the system.
Get your antifreeze out. If you bought undiluted, mix it with water so that the coolant blend does not exceed equal parts with distilled water. The ideal is 50/50.
Make sure your system is closed again from your last flush procedure and fill the radiator with the mixture. Start the car and add more as necessary until the car has reached its capacity of 7-1/8 quarts.
To “burp” the system of air bubbles, raise the front of the car or park on a relatively steep incline so the radiator filler neck is at the highest point of the system, and run the car without the cap until no more bubbles appear at the opening. Shut the car off and cap the radiator, you should be good to go!