Answer first
A fake IW371665 is a counterfeit copy of an IWC Portugieser Chronograph. The number sits inside the IW3716xx reference block. That block covers a 41 mm steel chronograph with an in-house automatic calibre. Counterfeit copies of IW3716xx watches sell from about $300 to $1,200 on replica sites and marketplaces. Genuine steel Portugieser Chronographs trade for several thousand dollars. A seller asking $500 for a new IW371665 is selling a fake.
What the reference block contains
- Case: stainless steel, about 41 mm wide and 13 mm thick
- Dial: two subdials stacked at 12 and 6, small seconds below, chronograph minutes above
- Movement: IWC calibre 69355, automatic, column wheel, about 46 hours of power reserve
- Crystal: sapphire front and back on the modern generation
- Water resistance: 3 bar
- Strap: alligator leather on a steel pin buckle, or a steel bracelet on some references
IWC does not publish a full archive of every reference number. Open sources list IW371665 among the IW3716xx Portugieser Chronograph references. The exact dial color and strap for that single number cannot be confirmed from public material. Treat any IW371665 listing with a dial that does not match the reference family as a mismatch, not as proof.
Checks that catch most fakes
Case and proportions
Measure the case. Fakes run 42 to 44 mm because the makers reuse a generic shell. Compare the lug width: 20 mm on the genuine watch. Look at the lug tips. Genuine lugs curve down and sit against the wrist. Fake lugs sit flat and sharp. Check the crown and pushers. IWC uses a signed crown with a deep relief IWC mark. Fakes use a laser etch that fades under a loupe.
Dial printing
Genuine dial text is thin and crisp. The IWC and SCHAFFHAUSEN lines share one baseline with even spacing. Fakes show thick, soft type. Applied numerals on the genuine dial have polished bevels. Fake numerals look flat and gray. Subdial spacing is the second tell. On fakes the two subdials drift toward the center because the base movement differs from calibre 69355. On the real watch the subdials sit low and high with a wide empty band between them.
Movement and caseback
A sapphire caseback shows the movement. Genuine calibre 69355 has Geneva stripes, blued screws, and a skeletonized rotor with the IWC logo. Copies in this price band use a dressed generic movement with a printed rotor. Check the balance rate: 28,800 vibrations per hour, 4 Hz. A slow, wobbling balance points to a cheap movement. Caseback engraving on the genuine watch is deep and even. Fake engraving is shallow, and in many cases the reference number is stamped with the wrong digits.
Documents and box
Genuine watches ship with a warranty card, a manual, and a box matched to the reference. Counterfeit kits copy the card layout and miss details: wrong font on the date, no dealer stamp, and a serial that does not match the caseback. Call an IWC boutique with the serial number before you pay.
Price test
Steel Portugieser Chronographs on leather list near $8,000 USD and trade on the secondary market below that. Prices move. Any offer far under the market range is a fake or a stolen watch. Neither is a good purchase.
What a photo cannot show
Photos hide movement noise, crown feel, and weight. A 41 mm steel watch on a strap weighs about 80 to 90 grams. Ask for a video with the chronograph running, a photo of the caseback serial, and a timed rate check. Refuse to pay without an inspection window or an escrow service.