How To Bypass the Under-Plenum Coolant Hoses On Your Z32 300zx NA

by Robert Sidaway on June 17, 2023 Categories: 300zx How To

The Z32 300zx comes from the factory with a number of coolant hoses running beneath the upper intake manifold (upper plenum); the purpose of which is to warm the throttle mechanism in extremely cold climates. These coolant lines are not needed in the Autralian climate, and are commonly removed during what is colloquially referred to as a "plenum pull". I couldn't find an article on completing this procedure for Non Turbo, so I decided to snap some pics of a recent job. 

This article assumes that you already have the plenum removed. If you are not sure how to go about this please consult one of the articles available in the tech section at

With the plenum removed you can completely remove all of the barbs and tubes assosciated with the cooling system as shown below. The barbs can either be cut off with a hacksaw or similar, or removed with a punch and hammer. 

The picture below shows the outlets on the heater pipes that will now need to be reconnected. There are three outlets on the rear of the motor, and one on the Left Hand Side of the motor behind the exhaust side valve cover. These are circled in blue below.

To complete the procedure we will be using one of my NA Coolant Hose Bypass kits shown below. This includes heater hose cut to length, and four solid hose clamps. The process is the same if you are using your own parts. 

I have seen examples where these outlets have been capped, and while that is a possible alternative I have found that rubber caps (typically designed for air systems) do not have the heat and chemical resistance of heater hose. My preference, therefore, is to complete the circuit as per factory.

The first connection we are going to make is from the lower barb on the RHS heater pipe to the upper barb on the LHS heater pipe.

The lower clamp can be tricky to access, my preference is a 6mm hex socket on a 1/4" long extension. 

The second hose connects the lower barb on the LHS to the upper barn on the RHS as shown below. The length of hose supplied with the kit is long enough to route underneath the VTC solenoid and around the back of the motor. 

Use cable ties to keep the hose away from any sharp edges if needed.

My final recommendation is to pressure test the cooling system prior to installing the plenum. It is much easier to rectify a mistake while the car is still in pieces than it is to have to start over...