Originally Posted by pefrey
This is what I am trying to understand. Jeep routed the line the way they did for a reason that evades me. I don't see how running behind the engine would expose the line to higher temeratures than running next to the exhaust headers. Also, I could wrap the line in this:
JEGS Thermal Heat Sleeving - Free Shipping on All Orders @ JEGS
Heat wrap is a band aid solution that the engineers probably dismissed at the outset. They were using a metal line that acts like a heat sink. Too near the engine on a firewall or otherwise and the DOT3 or even 4 fluid will get real hot, real fast. On a Wrangler, that area between the firewall and back on the engine has poor air circulation and gets very hot, especially in the summer. Not hot enough to boil the fluid (which has a boil point of just over 400 F) but will get hot enough to possibly degrade performance. A lawsuit waiting to happen to Jeep I think, so they went around the frame instead. Also, that line as routed along the frame never really runs close enough to the headers to be an issue. Plenty of space and air swirling around to dissipate any heat transfer while the line runs along the frame. Then it gets cooled at the front of the Jeep anyway.
For example, I also have a Nissan 350z. The clutch fluid line uses DOT3 inside a rubber line and runs very close to the exhaust manifold pipes on its way to the tranny. Nissan heat wrapped the line with basically the same type of sleeve in the link above. Guess what, on a really hot day in traffic the fluid gets too hot and my clutch peddle gets soft and sometimes sticks halfway down. That's a design flaw that a lot of guys with Z's experience. I had to go to DOT4 fluid with a higher boiling point and myself added a TON of additional heat wrapping to the line just to get by on a hot day--and it still gets a little soft on a hot day. If it was a metal line, the problem would be even more amplified. Heat matters when you deal with anything brake fluid related.