Here is UPDATED information from Garmin Engineering on the WaterProofNess of the Garmin GPS-12XL AND other Garmin equipment as of (February 1999)
Compiled by Joe Mehaffey
Initial issue May 1997
Garmin Says:


GARMIN has worked diligently to make our marine products waterproof, and to put in place processes which would produce
waterproof products in a production environment. On a low cost product, this is no small task to undertake.

We have succeeded in making new products such as the GPS 12XL waterproof, and this product is now certified waterproof under IEC IPX (level 7), which means waterproof under full submersion to a depth of 1 meter for 30 minutes.

Exception Note:  The case to the GPS 48 is the same design as that used in the original GPS 45. This form factor has been
extremely popular, and resulted in the sale of over 400,000 GPS 45's, which I suppose is why we continued the same case style with the GPS 48.   The G-45/48 case design does not lend itself to to being able to obtain a consistent watertight seal in a high production manufacturing environment. For this reason the GPS 48 is only able to carry an IEC529 IPX4 rating (basically splash proof, rather than immersible).   Almost all of our new production units are rated fully submersible to IPX7.

Having a unit such as the GPS 12XL this watertight is not all a bed of roses. Watertight also means airtight. When temperature
and pressure changes act on a watertight (airtight) unit,   pressure differentials develop. Undesired effects can occur,   like the buttons being drawn down inside of the unit, or the lens over the display bowing out and potentially cracking.

During further process improvements, it became necessary to allow the unit to "vent", to prevent these undesired effects from
occurring. To accomplish this "venting", we drilled a small (1mm) hole in the case of the unit and covered the hole with a
hydrophobic membrane. This membrane allows air to pass but not water, resulting in a unit that is still waterproof, but one that
can also equalize pressure differentials.

Though we didn't learn this from them, we have noticed that Lowrance incorporates this same type of vent in their products
such as the Eagle Explorer.

Now that the unit is able to vent itself, obviously it will also  allow a 100% fill of dry nitrogen to also equalize itself to the
atmosphere's nitrogen content. So we no longer dry nitrogen fill the GPS 12XL as it would leak out anyway.

Recently, Garmin provided the following additional information.

1) Effective November 1996, all of Garmin's production of  commercial GPS units has been changed over to a design which
incorporates a "hydrophobic membrane" to allow the GPS enclosure to equalize pressure inside the case with the pressure outside.   This reduces the likelihood of differences in pressure either blowing the case's seal or causing keys to stick.

2) Garmin now factory tests the GPS MAP 175, 38, 12, 12XL, II, II+, and all the fixed mount GPS units (120, 125, 130, 135, by  "proof" testing by applying a vacuum. We have established a good correlation between the ability of the unit to hold a vacuum and the ability to pass an immersion test per IEC 529 IPX7.

3) Garmin states: "We believe we have advanced a lot in the area of waterproofness and have folded a lot of that into existing
products like the new GPS 38 which you might notice is now black and in the same plastic shell as the 12XL. It is also tested for waterproofness and uses the same assembly processes as the 12XL,  but we don't test as many of them due to the higher volume. So,  although we have not advertised as such, the 38 is now designed to be immersible per IEC 529 IPX7 also (30 minutes under 1 meter - same as JIS 7)."

Thank you and best Regards,

GARMIN International
1200 E. 151st Street
Olathe, KS 66062 USA
As of 1999, ALL of Garmin's outdoors and marine products (including the G-III, G-III PLUS, and G-12CX) AT A MINIMUM are designed to meet the IEC 529 IPX7 submersibility specification.  The exception is the G-48 which is designed to IPX4 (splash proof).