M42 "Mess under the intake"

The M42 "Mess under the intake" modification is a process used on E30(1989-1991) and E36 (1992-1995) 318i and 318is. That is, any BMW with the M42 four cylinder motor. The M42 is an evolution of the M40 four cylinder used in the early generation E30s. The M42 is a decently reliable motor given that attention is paid to its cooling and timing systems, and the only real shortfall is the tangle of cooling and vacuum hoses underneath the intake. The simplification involves deleting the heater plates used to warm the throttle body (a last minute addition used to pass emissions when the motor was launched. To do this job I followed the guidelines of various forums and this diagram. (Figure 1)

This project initially looked overwhelming, but I learned while taking everything apart that it is really quite simple. Here's what you'll need to do this job.

Plastic Coolant Pipe from Block (Part # 11531714738) *NOTE: Make sure this is OEM! Aftermarket pipes have been found to leak, as noted here* • O-Ring for Pipe (Part # 11531709157) • Throttle Body Gasket (Part # 13541743261) • Upper – Lower Intake Gasket (Part # 11611717761) • Lower Intake – Block Gasket (Part # 11611734684) • BMW Antifreeze (Part # 82141467704) • 5/8” Coolant Hose • 5/16” Fuel Hose (Make sure it is fuel INJECTION hose, not fuel hose for a carb) • 19/32” Vacuum Hose

Source

Step 1: Remove throttle body, upper intake, lower intake, hoses, and fuel lines. Pull the heater plates (the two pieces of metal marked in purple in figure 1). Do not forget to plug the intake holes with paper towels so as to prevent any debris from falling into the cylinders. Clean any parts and replace temperature sensors if desired. When disconnecting the fuel lines, some gas will come out. (A guide to cleaning injectors here)

Step 2: Replace the Plastic Coolant Pipe and route 5/8" coolant hose (Light blue hose in Figure 1) from the pipe to the cylinder head. I used a piece of hose from the old system to shim the heater hose down to the smaller nub off of the cylinder head.

Step 3: Remove the paper towels and attach the lower intake to the cylinder head with a new gasket. I routed the bypass coolant line underneath the lower intake and did my best to keep major bends out of the hose. At this time replace the rubber fuel lines with new ones and reattach the metal fuel lines.

Step 4: Attach the upper intake with gasket. Attach the ICV (below)to the upper intake.

Route a 19/32 vacuum hose from the ICV to the elbow nub right after the air box. On the valve cover route a 19/32 vacuum hose to the throttle body nub.

(Orange hoses in Figure 1)

Step 5: Attach the throttle body, without the heater plates, to the upper intake. Don't forget a new gasket here either. Check that all hoses, sensors, and assorted parts have been connected and tightened. All coolant hoses should have hose clamps on them. I also used hose clamps on the vacuum hoses as well, but this isn't necessary. I also replaced the vacuum hose from the fuel pressure regulator to the throttle body.

Step 6: Bleed the cooling system. This is done by lifting the front end of the car about a foot, opening the bleed screw at the top of the radiator next to the overflow tank, and adding coolant to the overflow tank until the bubbles stop coming out of the bleed hole. The car should be brought to temp with the heater on and then bled again. (Alternate explanation)

This guy recommends a couple other things that can be done at the same time.

That's all. Check for leaks and enjoy a fresh and simplified system.