PRODUCT DETAILS
SpeedFactory Upper Coolant Fill Neck - Honda D Series Engines
Running a custom radiator setup or SpeedFactory tucked radiator on your D series engine? You need a proper way to fill your cooling system from the highest point, or you'll never get all the air out. This SpeedFactory upper coolant fill neck relocates the high point of your cooling system so you can fill and bleed it properly. It bolts to your cylinder head where the factory upper coolant passage is, and it gives you a proper filler neck with a radiator cap at the highest point in the system. No more trying to burp air out of a radiator that's mounted low in the chassis.
Why You Need a High Point Fill Neck
Air rises. If your radiator cap is lower than the top of your engine, you'll never get all the air out of your cooling system. Air pockets get trapped in the head and block, which causes hot spots and overheating. A proper fill neck at the highest point of the system lets air escape when you fill the coolant, and it makes bleeding the system way easier. This is critical on tucked radiator setups where the radiator is mounted low and there's no good way to fill from the high point without a fill neck like this.
Laser Cut Head Flange for Perfect Fit
SpeedFactory manufactures these fill necks in-house using high quality aluminum. The head flange is laser cut to match the coolant passage on D16 cylinder heads, so it fits perfectly every time. You're not dealing with gasket leaks or misaligned flanges. Just bolt it to your head with a new gasket and you're done.
Two Outlet Configurations
SpeedFactory makes this fill neck in two different outlet configurations to work with different radiator setups:
-16AN Outlet
Use this version if you're running -16AN braided hose or hard lines to your radiator. The -16AN fitting gives you a clean, leak-free connection to your cooling system plumbing.
32mm Standard Hose End Outlet
Use this version if you're running standard 32mm radiator hose. This is the most common setup for tucked radiators and custom cooling systems using rubber hose.
OEM Bolts Don't Fit
The factory upper coolant neck flange bolts are not compatible with this fill neck. You need M6 x 1.0 x 16mm button head socket cap screws to bolt this fill neck to your head. Don't try to use your factory bolts, they won't work.
Requires Type A Radiator Cap
This fill neck uses a Type A radiator cap interface. You need either a SpeedFactory Type A radiator cap or a Hybrid Racing Type F radiator cap (Type F and Type A are the same). Don't try to use a Type B cap on this fill neck, it won't fit.
What You Get
- SpeedFactory upper coolant fill neck for D series engines
- Manufactured in-house from high quality aluminum
- Laser cut head flange for perfect fit
- Relocates high point of cooling system for easy filling and bleeding
- Available in -16AN or 32mm standard hose end outlet
- Type A radiator cap interface
Compatible Engines
- D16 engines (all variants)
- D16Z6 (1996-2000 Civic Si, Del Sol VTEC)
- D16Y7 (1996-2000 Civic)
- D16Y8 (1996-2000 Civic)
Available Configurations
- -16AN outlet (for braided hose or hard lines)
- 32mm standard hose end outlet (for rubber radiator hose)
Required Components
- SpeedFactory Type A radiator cap or Hybrid Racing Type F radiator cap (not included)
- M6 x 1.0 x 16mm button head socket cap screws (not included, factory bolts don't fit)
- New head gasket or coolant passage gasket
Important: This fill neck is for D16 engines only. Factory upper coolant neck flange bolts are not compatible - you must use M6 x 1.0 x 16mm button head socket cap screws. Requires Type A radiator cap (SpeedFactory Type A or Hybrid Racing Type F). Use a new head gasket or coolant passage gasket when installing.