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L-Head Water Pump Replacement

Author: Code3TJ

When I bought my 1948 Willys CJ-2A, it hadn't been started in six years. The previous owner had mentioned that it leaked a bit of coolant from the front of engine, but he wasn't sure exactly what was wrong. Amongst all the extra/spare parts was a new water pump. That should've been my first clue.

View of water pump and fan from driver's side of engineSince it had been sitting for so long, I began inspecting the belt and hoses. As soon as I touched the fan belt, the water pump let go. Antifreeze poured out of the bearing and shaft. I decided that replacing the water pump would be the first order of business in an effort to get it running again. Unfortunately, I didn't take very many pictures - just not enough hands.

The procedure should be very similar for any Jeep or Willys with an L-head 4-134 "Go Devil" engine including the MB, CJ-2A, CJ-3A, CJ-3B and some CJ-5 and CJ-6 models.

Before we begin, a couple of warnings:

Never open the cylinder block drain plugs, radiator cap or open the petcock while the engine is hot or the cooling system is under pressure. You're likely to burn yourself. Also, antifreeze is poisonous. Children and animals are attracted to it due to the color and odor. If you suspect a child has consumed any antifreeze, immediately call 911 or your local poison control center.


Loosen the bolts on the guard beneath the oil pan to free the fan belt1. The first step is to drain the cooling system. Find a suitable container and dispose the used antifreeze appropriately. DO NOT pour it into the gutter or down a storm drain. Check with your local water district or garbage company to determine the appropriate method of recycling used antifreeze.

2. Disconnect the hose at the water pump. The hose was stuck to the pump and since I was replacing it, I used a razor blade to slice the hose perpendicular to the hose end. If, when replacing a hose and it becomes stuck, do not force a screwdriver or other sharp tool under the hose end. Use the razor blade and slice the hose being careful  to make a shallow cut.

3. Remove the fan belt. I loosened the alternator bolts to release the tension on the belt. After you've loosened the alternator bolts, move it on its pivot point to free the belt. I found a skid plate/guard on the leading edge of the oil pan which prevented me from removing the belt. I loosened the guard's bolts enough to free the belt.
The water pump with the fan removed
4. Unbolt the fan. Remove the bolts attaching the fan and any spacer from the pulley.

5. Remove the pump. The water pump is held on with four bolts. Remove the bolts keeping a catch pan beneath the engine. When you break the seal between the engine and the water pump, coolant will likely leak out of the block.

6. Thoroughly clean the pump mounting surface of old gasket material.

Remove the old gasket from the front of the engineCleaned engine


The installation is not surprisingly the opposite of the removal.

The old and new water pumps1. I used Permatex RTV to make a gasket on the new water pump before installing it. Basically, I ran a bead of RTV around each opening on the mounting surface of the pump. The bolts should be tightened to 17 ft/lbs (23 Nm). I did run into a slight problem with this step. It's obvious that several people have worked on the engine over the years. I found 3 of the 4 bolts were different sizes.

2. Reattach the fan (and spacer, if there was one).

3. Install the fan belt. Route it correctly over the various pullies. Once you have the belt on, tighten the bolts on the oil pan guard before you forget about them Tighten the alternator belts and adjust the fan belt. To adjust the belt, I place a straight edge across the pullies at the longest straight run of belt. Pull (or push) on the mid-point of the belt between the two pullies and measure the distance between the straight edge and the belt. You should be able to move the belt inward (deflect) between 3/8 and 1/2 inch (9.5-12.7mm). Once you have the belt adjusted properly, tighten the alternator bolts.

4. Dip the radiator hose end in clean antifreeze to make it easier to install the hose. Slide the clamps over the hose ends before attaching it to the radiator and water pump then slide the clamps over the connections. Tighten them.

5. Close any draincocks you've opened. Fill the radiator with to within 1/2 inch of the fill neck with your favorite mixture of water and antifreeze. Run the engine until it reaches normal operating temperature to bleed the system of air. Make sure that there are no leaks and you're ready to go!

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