Jeep Wrangler Cooling System: Overview Guide

A cooling system is comprised of six main parts:

• Radiator
• Thermostat
• Water Pump
• Hoses and valves
• Inlet and outlet tanks
• Radiator cap

Your coolant is designed to absorb heat from the engine block. Coolant is pushed through the engine block via the water pump and then through a series of fins and tubes inside the radiator that allow the heat to dissipate. 

The thermostat regulates what temperature your coolant is allowed to reach before it’s pulled from the engine block and then circulated through the radiator again. 

A car radiator is a heat exchange that cycles thermal energy through the radiator fan to release heat from the engine block and around the radiator. This is why it’s incredibly dangerous to open a hot radiator cap because immense heat and pressure can build up. 

Radiators are mounted behind the grille of your Jeep to intake high pressure air during travel. Radiator fans are not always required on newer Jeeps, although YJ Jeeps typically used an electric fan. Most Jeeps today have a mechanical fan that’s mounted directly to the engine. One thing to keep in mind is an engine with low or tarnished coolant can cause significant friction within your radiator and damage internal components across your Wrangler. 

It’s important to check up on your radiator and cooling system every now and then. This can be judged by coolant levels, although excessive coolant loss is usually the result of a leak in a tube. Radiators come in all different shapes and sizes so you should only buy a radiator designed for the year and make of your Wrangler. While universal fit radiators are prevalent, they’re not ideal for your Wrangler. Bigger radiators provide greater cooling power and can keep up with the intense driving tasks you take your Wrangler on.

The density between the fins in your radiator (fin density) determines how effective your radiator can perform as a heat exchange. Fin density in newer radiators typically lies between 18 or 20 fins per inch (FPI).YJ Jeeps ran using 9 to 15 FPI, which is why it’s important to purchase modern radiators able to keep up with the heat generated from newer engines. A greater FPI leads to increased cooling capabilities, but a high FPI can also restrict airflow in a dirty radiator. 

Consider the performance value that a healthy radiator provides for your Wrangler:

• Reduces air intake temperatures
• Prevents overheating
• Increases engine power and torque
• Provides longer oil life

Understanding the different parts of your radiator will help you to find an aftermarket replacement that will add extra performance for your Wrangler. For this purpose, you don't really need to know about some of the nitty-gritty parts, such as the header plates and filler neck. 

It’s also important to note that automatic transmissions often feature an added cooler to help regulate transmission temperatures. They serve the same purpose as your main radiator to help eliminate heat from transmission fluid. 

Radiator caps are the hottest parts under your hood because the cooling system uses pressure to prevent coolant or water from evaporating or boiling. The radiator cap is responsible for measuring and releasing some of this pressure, should it rise to the point that risks damage to other engine components. Removing your radiator cap can result in burns and, during vehicle operation, significant loss of coolant. 

The pressure cap contains a spring set to 15 psi that forces the valve of the cap to open under high pressure. Once this happens, excess coolant flows to the overflow tank and then returns once the coolant has cooled. 

If you’re confused about the difference between vertical and cross-flow radiators, there isn't much difference. Both provide about the same amount of cooling performance, but the vertical flow radiator is more sensitive to boil over without the proper configurations.

Vertical flow radiators position the cap on the high pressure side of the radiator. You’ll need to adjust the spring pressure if you install a high flow pump to prevent overflow. Horizontal or cross-flow radiators fixed this by moving the radiator cap to the suction side of the pump to prevent boil over. This means a high flow pump can work without any damage to your cooling system.

Cores are composed of fins, or heat conductors, that regulate heat transfer within the radiator. Cores are either made of copper or aluminum. Radiators are often identified by the number of cores they contain. More cores in a radiator is indicative of greater cooling capabilities, although this isn’t always true. 

Most vehicles feature single or double core aluminum radiators, while copper radiators often feature three-core or four-core radiators. Multiple core radiators don't actually mean more cores, but more rows. For example, a thick, four-core radiator would have four rows running horizontally through the core. Thick radiators can sometimes restrict air flow use by design, which makes it important to do your research first. This will mainly depend on the construction of the cores and radiator itself.

There are two tanks located on opposing sides of your radiator. The inlet tank feeds coolant into the engine, while the overflow tank keeps hot coolant in reserve until it’s cool enough to reenter the cooling system. They are made of hard plastic and have varying capacity depending on your Wrangler’s make and model. 

Many people still wonder if copper-brass radiators offer any added vehicle performance or why they’re widely extinct nowadays. Copper-brass radiators were very popular on old vehicles up until the 1980s.

You’ll be hard pressed to find one on a Wrangler TJ though. While copper is a great heat conductor, copper-brass radiators were subject to overheating and ballooning. To prevent this, many were manufactured with tubes containing small diameters, which severely limited cooling performance.

Aluminum radiators provided a harder shell, allowing manufacturers to increase the diameter of radiator tubes for better coolant flow. Aluminum radiators were also lighter so they didn’t impede engine performance and they decreased row quantity.

By decreasing the row quantity of aluminum cores and increasing tube diameter, single-core aluminum radiators were significantly more efficient than four-row copper-brass radiators. 

While more rows in an aluminum radiator does provide better cooling performance, it also restricts air flow. Single and double-core aluminum radiators provide better airflow and cooling capabilities by eliminating the number of rows copper-brass radiators needed. This also meant less stress on the radiator fan, allowing it to displace heat more effectively. 

A larger tube diameter allows for more coolant to flow through the engine block. Many radiators now have 1-1.5 inch. tube diameters. However, increasing tube diameter past this point would require a turbulator fin to ensure that coolant still touches the fin upon transfer. Increasing tube diameter past this point would not increase cooling capabilities all too much and you should be fine with a 1-1.5 inch. tube diameter and double-core radiator design. 

Generally, each generation of Jeep had much of the same coolant capacity. Most 4.0L engines hold about 6 quarts of 10W-30 coolant, although the 4.0L JK series requires 5W-20 coolant. For more information about your coolant capacity check out our coolant capacity chart.  

One fallacy people harbor is that reducing their radiator thermostat improves cooling performance. They think less heat, cooler air, greater combustion, and therefore more power. 

Only your engine is designed to run at a certain temperature so knocking your thermostat down beneath 170 will not be able to keep up with the heat generated from your engine. Most radiator thermostats are designed to run at about 200 degrees. This one should be obvious, but never take out your thermostat; this would defeat the purpose of your cooling system.

Keep in mind the thermostat is used to monitor the temperature of the coolant, hence why it's placed between the engine and the radiator. If the coolant is not picking up enough heat from the engine, the thermostat will register the lower temperature, and close a valve to prevent the coolant from flowing to the radiator. This forces the coolant to absorb more heat from the engine. 

My father used to tell me that if you’re ever low on coolant during the summer and need to drive somewhere, just use some water. That might have been a good idea a few decades ago, and it’ll get you to where you need to go. 

But, water has minerals that corrode the precious metals in your cooling system and can even obstruct pumps and valves flowing from your engine and radiator. I never suggest using water as a replacement for coolant, especially in extreme climates. 

Coolant itself is composed of a 50/50 mix of antifreeze and deionized water. Deionized water is clear of any minerals and won’t obstruct your cooling system’s integrity. The antifreeze is designed to lower the freezing point of your mixture so it won't freeze during the winter. It also raises the boiling point so it won't overheat or boilover during intense engine operation. 

The water pump is the central pump in your cooling system that injects coolant mix directly into the intake manifold and into your engine. The water pump is powered by the accessory belt of your engine, which circulates on the water belt pulley. 

These pulleys are located next to your water pump, connected to the water pump housing. Water pumps are very sturdy and last for several years. You can check on the status of your water pump every few months by checking the weep hole.

If coolant is dripping from the weep hole then it’s a sign your water pump is starting to give. You can also pinch the radiator tube once the engine is running to see if coolant is pumping through your system. Be sure to check your accessory and serpentine belts for wear to see if there are any other internal issues affecting your cooling system. 

Replacing a water pump is fairly inexpensive. It's also necessary if you don't want to end up stranded anywhere. A mechanic may run you about $400 or you could save some money and do it yourself.

To replace a water pump you’ll first need to disconnect your battery, remove your serpentine belt and dislodge your water pump pulley. To remove the serpentine belt you’ll need to insert a ratchet bolt into the tensioner hole of your serpentine belt, which is located in the middle of the alternator pulley. It’ll be a square hole in the center. Using the ratchet bolt, push the tensioner to the right to give the belt some slack in order to slip it off.

The water pump pulley will require you to remove three bolts. These will be easy with your ratchet, but you’ll need to insert a screwdriver into the holes to keep the pulley from spinning. Once that’s over, you can disengage the water pump. You’ll need to take out seven 10mm bolts with a ratchet and socket. 

These are aluminum, so be careful not to bust them. Have a catch basin ready to catch any coolant that spills out. Now you can remove the water pump. Remove any old residue from the gasket and spray some new sealant into the mounting area. Insert the new gasket and water pump and line it up with the mounting holes. Once in, give the bolts some torque to make sure they’re tight.

When placing the water pump pulley back on, you’re not required to give them torque, just tighten them. Finally, you’ll need to give the alternator pulley some slack by inserting your breaker and ratchet into the tensioner hole. Once enough slack is created, slip the belt back on and return the tensioner pulley to its normal position. 

Oil coolers can provide additional cooling capabilities to your Jeep. An aftermarket oil cooler is essentially the same as the transmission cooler and seeks to regulate the temperature of your oil. Install a temperature gauge to ensure your oil cooler is running your oil at an optimal temperature. 

Running oil too cool increases its viscosity and makes it harder for heat to burn off contaminants in the mixture. These are mainly designed for off-roaders, racers, or to use on an incredibly hot day in the summer. 

The cooling system seeks to push out heat from your engine block to prevent internal parts from overheating. We all understand that fuel provides our car power by converting to heat. Internal combustion engines thrive on heat, but even the mechanical parts and internal fluids that flow through your engine block can start to boil and crack if the temperature is not regulated.

The cooling system functions by sending liquid coolant (antifreeze) through the engine block and heads, in order to pick up the heat released from the working engine. The hot fluid moves through the rubber, interconnecting hoses towards the radiator in the front of the vehicle, where the air entering the car’s grill will cool the liquid. The cool fluid will then return to the engine to repeat the process, with the help of the water pump to keep the fluid moving smoothly.

We've talked a little about overheating, but what are all the risks involved during an overheat? For starters, if your Jeep still has coolant, the antifreeze remaining can boil, expand, and burst radiator hoses. The extra heat can also warp or melt components of your engine/engine compartment, especially those made of aluminum. By continuing to drive with an overheating engine, you risk warping a cylinder head, which causes decreased power, oil leaks, misfiring, or excessive burning of oil. Welds, seals, sensors, wiring, belts, and parts such as the fuel pump and steering column are all at risk of damage as well. Finally, in addition to all of these hazards, driving with an overheating engine has the potential to blow the head gasket. When this happens the antifreeze mixes with the oil, and your engine is destined to inevitably fail. This is the most expensive repair all car owners dread.

Should your rig start to overheat, there are several possible ways to prevent damage. 

If you can safely stop:

• Pull over the moment you see steam coming from your engine
• Open the hood to allow the heat to disperse 
• Do not open the radiator pressure cap (due to risk of serious burns)
• Turn your heater on full blast
• Check coolant reservoir system (and refill if necessary)
• Look for a leak in the coolant system
• Decide whether it is safe to continue driving, or if you must call for help

If you must continue to drive:

• Turn off your air conditioning
• Use your heater to disperse excess engine heat
• Monitor the temperature gauge
• Maintain a steady speed, or pull over if not possible (such as in stop-and-go traffic)