The following post comes to us courtesy of Mugen aficionado Jerimiah Styles! Many thanks to him for another contribution of his time and insight!
In this post Jerimiah covers some of the differences he's observed with the Mugen Hi-Pressure Radiator Cap. Note that there are two genuine versions of this cap:
Del Sol (1993-1997)
RSX Type-S (02-04)
RSX Base (02-06)
RSX Type-S (05-06)
(this version displays "B2" on the decal and fits Koyo radiators)
This is the way the part is described in our King Motorsports / Mugen 1999 Mugen Pricelist for Integra (19045-XGER-0000):
This radiator cap is a high-pressure type that increases the pressure inside the radiator, thus raising the coolant boiling point and increasing the cooling efficiency. The open valve pressure is 1.3 kg/cm2 compared to the normal 1.1 kg/cm2. It demonstrates its power under high-load situations such as circuit driving.
The genuine Mugen cap comes in the traditional Mugen window box with Mugen stripes across the top, and high quality foam to protect the product. Printed Japanese instructions are included.
The back of the genuine part has the typical characteristics of all genuine Mugen parts, kanji in the top left corner and sticker with part number and M-Tec information.
In this below image, this fake window box is entirely different from its genuine counterpart. These knock off companies are always evolving and continually getting better at their packaging, getting closer and closer to the authentic Mugen boxes. Always look at the part itself and its distinguishing signs to discern if the part you are buying is indeed real.
Here is a close up of the genuine cap. The authentic Mugen cap is high quality metal, nicely polished, but not a chrome finish. There are no indentations or stampings on this cap. The decal has a metallic foil quality with golden letters in the red area along with "NEVER OPEN WHEN HOT" printed in white, and a brushed metal look to the script in the black portion.
Now here are a sample of the many fakes that are out there. Fonts, font colors, printing quality, decal size, decal placement, and stamping on the metal are all indicators of a fake. We recently discovered a company on eBay selling just the decal!
Here are a few pictures of the genuine cap's bottom and the included instruction sheet:
Why does it matter?
The Mugen Hi-Pressure Radiator Cap is more than just engine dress-up. It's a functioning part that increases your open valve pressure to a specific 1.3 kg/cm2 for performance reasons. Those that use fakes are not only missing out on performance benefits, but have no idea if the cap has even been manufactured to meet OEM standards. The open valve pressure can be too high, too low, or inconsistent. Fakes can come apart due to bad seals and assembly, causing nasty spills and other headaches.
Visit the King Motorsports store for genuine Mugen hi-pressure radiator caps!