My only experience with DOT 5 was helping a neighbor restore a mid-70s FMC (Food Machinery Corp.) RV, that a previous owner had converted to DOT 5. This vehicle was from Phoenix, AZ and all of the cylinders were ruined by rust, apparently resulted from water layering out as I recall beneath the silicone. How that vehicle got that much moisture in the cylinders I don't know, maybe it was stored in a lot that flooded during our summer rain? He had to replace the whole system.
From my perspective, DOT 3 or 4 is hygroscopic which means it absorbs water. This is actually good, at least to a point, so that a little water does not affect performance or cause pooling and any water can be removed by periodic bleeding. Periodic bleeding is really very simple and inexpensive, so routine maintenance will remove any moisture that gets in and you won't have rubber problems like you might with DOT 5. My 2016 Silverado uses DOT 3 so the engineers must think it is still a good choice (or was GM just trying to save a dollar or two on each truck?).
Clearly, many people have had success with DOT 5 and I would not try to convince them otherwise, especially if it was installed in a new system. A skeptic would rightfully claim my apparent fondness for DOT 3 might stem from the fact I live in a very dry area. although I would point out that my '92 Jeep Wrangler crosses creeks and washes and the brake system has been maintained in fine shape by routine bleeding of it's DOT 3 system.
Kent
Last edited by Lightholder's Dad; 06/09/2021 5:25 AM.
