CA18DET Water Mod (Simplifying Water Circulation)


New simplified coolant mod number 2 available here. CA18DET Coolant Mod Number 2 (From 10 Lines to 1)

One thing I value on a car that will see serious track time is weight reduction and simplification. This mod focuses on simplifying the water circulation system to improve it’s reliability and greatly reduce it’s complexity.


This mod is perfect for the racer looking for ultimate performance. For instance, I am a big fan of weight reduction in any car. The less weight a car has the less mass any wear item on the car has to move or stop. In other words, less weight = quicker acceleration, shorter stopping, improved agility and less wear. As such, my 240sx hasn’t had AC, heat or interior since day one. Also, I am going to show how to block the turbo water lines. Contrary to what most think, it is not necessary to liquid cool your turbo. The main reason turbos are liquid cooled is to avoid coked oil due to improper oil change intervals and neglected cool down. For anyone tracking their car, this typically isn’t an issue. The liquid cooled center section is designed for your mom driving the turbo Volvo.


To understand how the cooling system works on the CA18DET check out the CA18DET Vacuum, Boost, Water and Oil Routing Reference. With an understanding of how the 8 water lines function on the CA, I am now going to show you how to get this maze of lines down to one.

Turbo Side

To begin, drain the fluid from the radiator and remove the water line going from the turbo to the block and the line from the turbo to the intake manifold. Remove the factory water inlet on the block and use a 1/2″ plug* (found in the plumbing section of your local hardware store) to plug the hole.

Water return from the turbo on the ca18det motor.

#3 in this image is the water inlet from the turbo with the 1/2″ plug installed.

* Note: I blocked the water inlet on the turbo side when the head was off of the motor. You may not be able to remove the factory adapter with the cylinder head attached. If this is the case, auto parts stores usually sell npt fittings in the back so bring the factory water return bolt from the hard line and find an appropriately threaded plug.

Intake Side

Remove all of the water lines from the intake side except for the radiator hoses. This includes the bracket below the intake manifold and both heater core lines. Locate the metal t on the lower radiator hose and cap the outlet. I used a short length of 5/8″ hose and a plug to cap this outlet. Now water from the lower radiator hose has only one path to follow and that is into the block. Next, cap the small nipple** on the t that functions as the outlet behind the thermostat housing and using 5/8″ heater hose***, connect the large outlet directly the the inlet on the block where the heater core used to connect.

The uper water route on the ca18det metor.

Cap nipple #3 and run a line from #4 to the block. (The thermostat housing is the blue unit connected directly to the upper radiator hose)

water inlet to ca18det block

#4 from the previous picture is plugged directly into #5 in this pic. This is the block inlet.

The finished water route on the ca18det.

This is the roughed in finished install on my motor. I rotated the lower t upwards to make bleeding the system a breeze. Air regulator not present.****

** Note: If you still want to liquid cool the turbo, you could run a line from this nipple along the front of your engine to your turbo and then keep the factory return line that was plugged in the first step.

*** Note: You will notice in some of the pictures that some of the hoses have a larger hose wrapped around them. This is done to protect the inner hose from rupture if it is located in an area that will see friction.

**** Note: The air regulator as well as the Idle Air Adjustment system has been removed from my motor and I simply have the throttle body set to a slightly open position for idle. The next tech article will demonstrate this system.

Finishing Up

Refill the radiator and check for any leaks. Start the motor and check for leaks again. And with that we’re done. Your CA18DET just got a lot simpler.

By 240am

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