How To Change the Oil Cooler on a WK2 Jeep Grand Cherokee Diesel

One of the most common questions we get asked is whether we have a DIY guide on how to change the oil cooler on a WK2 diesel Jeep Grand Cherokee.

We have done hundreds of these jobs over the years, but somehow we have never actually made a proper guide for it. So here it is.

For this demonstration, we had the engine out of the car. That makes it look far easier than it is in the vehicle, but the process is the same. The reason we filmed it this way is simple: with the engine still in the car, the body sits right over the area you need to work in, making it almost impossible to film properly.

So yes, it looks easy on the floor. In the car, it is much tighter, more awkward, and will take you a few hours.

Tools You Will Need

You do not need a huge tool kit for this job, but access to the part is the killer.

You will need:

• Quarter-drive socket set

• 10mm socket

• Needle nose pliers

• A universal joint for the socket

• Bucket or drain tray

• Razor blade if you are replacing the Z hose

A 3/8 drive may work for some of the bolts, but the bottom bolt is the issue. If the engine is still in the car, the air conditioning compressor sits in the way, and you will not get a 3/8 drive in there. A quarter drive is the way to go.

Step 1: Access the Cooler from Underneath

The first part of the job is easiest from underneath the vehicle.

If you are doing this at home, safely raise the vehicle and get underneath it. Make sure the car is properly supported before you start working.

The first thing to remove is the Z hose.

At GDL, we normally replace the Z hose rather than try to save it. It is often easier to carefully cut it off with a razor blade, then remove the rest once the cooler is on the bench.

The hardest part of the Z hose is usually the clamp at the end. If you manage to remove it without damaging the hose, good luck to you. In most cases, replacing it is the smarter option.

Also, have a bucket ready. There is a good chance coolant will come out when you remove the hose.

Step 2: Unplug the Sensors

Once the Z hose is out of the way, you will see the sensors on the back of the oil cooler.

On a Series 1 WK2 diesel, there is usually one switch.

On a Series 2, there are two switches.

Unplug these and leave the harness in the car. Do not forget about them, because forgetting to plug the sensors back in later is one of the most common mistakes people make on this job.

Step 3: Remove the Oil Cooler Bolts

The cooler is held on by four main 10mm bolts.

There is one bolt higher up and three along the bottom of the cooler. In a perfect world, they should all be 10mm. However, if someone has been there before you, there is always a chance one or more bolts have been changed.

The bottom bolt is the awkward one. This is where the quarter drive becomes important.

With the engine in the car, the air conditioning compressor makes access extremely tight. You may need a universal joint on the end of your quarter-drive socket to get onto it properly.

Take your time here. The bolt itself is not complicated, but the access is what makes the job frustrating.

Step 4: Remove the Cooler

Once the bolts are out, the cooler can come off.

This is also where you may discover what has been going on with the vehicle. In the video, the cooler had clearly been repaired previously using grey silicone.

Do not do this.

The gasket is cheap. Filling oil galleries or coolant passages with silicone is a terrible idea and can create far bigger problems later. If silicone breaks away and travels through the system, it can block small galleries and strainers.

On these engines, there is a small gauze inside the cooler that can block up. If the cooler is being reused for any reason, this gauze needs to be cleaned properly. However, in most cases, we recommend replacing the complete oil cooler assembly

Our recommendation is to replace the complete cooler.

When you buy the cooler, it comes with the gasket to mate to the block. From Jeep, that gasket is not normally sold separately from the cooler.

However, aftermarket gasket options are available. So if you are removing the cooler and refitting the same one for whatever reason, use a proper gasket. Do not use silicone.

Using silicone on this repair can cause major issues. It may seem like a quick fix, but it can end up blocking critical oil or coolant passages and creating a much more expensive failure.

Step 5: Refit the Cooler

Refitting is basically the reverse of removal.

One trick we use is to slightly loosen the two 8mm bolts on the bracket. This gives you a small amount of movement, which helps line up the four 10mm cooler bolts.

Once the cooler is lined up and bolted in place, make sure you tighten those two 8mm bolts again. Do not leave them loose.

Common Mistakes To Avoid

There are a few things that commonly go wrong when people do this job for the first time.

1. Forgetting to plug the sensors back in

This is very common. Before you finish the job, make sure the oil cooler switches are plugged back in properly.

2. Fitting the Z hose at the wrong angle

This is a big one.

If the Z hose is installed at the wrong angle, the wiring harness or switch can rub against the back of the hose. It may not leak straight away, but after around 10,000km it can rub through the hose and cause another coolant leak.

When refitting the Z hose, make sure it is not touching the back of the oil pressure switch or wiring.

This is especially important on Series 2 vehicles with the extra switch.

3. Using silicone instead of the correct gasket

Do not use silicone to repair this. Use the correct gasket.

The gasket is inexpensive compared to the damage silicone can cause if it gets into the wrong place.

4. Not cleaning the cooler gauze if reusing it

If the cooler is going back on, clean the internal gauze properly. If it is blocked, it can cause ongoing problems.

Changing the oil cooler on a WK2 diesel is not technically difficult, but it is tight and awkward when the engine is still in the vehicle.

You can do it with basic tools, mainly a quarter-drive socket set, a 10mm socket, and needle nose pliers, but expect it to take a few hours if you are doing it at home.

Replace the entire cooler if possible, use the correct gasket, do not use silicone, and make sure the Z hose and sensor wiring are positioned correctly when it all goes back together.

We have done hundreds of these at GDL Automotive, and most of the issues we see come from poor previous repairs, incorrect sealant use, or hoses rubbing through after being refitted badly.

Take your time, keep everything clean, and do it once properly.