I need to get something off my chest.

I have for years rolled my eyes at all the mentions of the “brittle plastic” coolant and vacuum lines in our trucks.

When I was in high school, long ago in a galaxy far, far away, I wore “unbreakable” nylon geekster glasses playing football and basketball. They were made of black nylon, and you could bend and twist the temples as much as you might (reasonably) like and they did not break.

The “brittle plastic” lines in our trucks are made of the same kind of nylon material.

Here is a pic of the coolant reservoir-to-throttle body heater line from my truck that’s no longer installed because I long ago bypassed the TBH. This afternoon I tied it into an overhand knot. No problem.




And yes, years ago I broke the brake servo vacuum line where it enters the upper intake when lying face-down on top of the engine my first time replacing the ignition cables, but that was an outlier. If you put enough pressure on any solid material it will break eventually. But these lines are in no way “brittle.”

Replace them with fuel line hose if you like – I don’t care – but understand you don’t need to do so because the nylon lines are brittle.

 

I spray a anti rust lubricant or wd40 in that engine bay every few months. Keeps things nice and moist

 

They definitely start off life being able to be bent like a noodle. They earn their reputation thought after being subjected to thousands of heat cycles. BMW used the same hoses in the same places, and yeah, after a long while, they'd break by flicking them with your finger. They do become quite brittle, just takes time.

 

Every single D2 or P38 I have ever opened the hood on in TX or owned = those plastic hard lines will crumble into millions of pieces like a safety glass window. I have never come across one that has lived it's entire life in TX without that issue. My brother lives in the PNW and he never has any of his LR plastics just crumble into pieces.

When it's new I agree the stuff is fine, but give it a few years and lots of hot/cold heat cycles and it will definitely become brittle.

 

that is a relatively new line. Try one that is 10years old, with constant 200*+ going through it. It gets real brittle

 

Nope, the line pictured is 20+ years old, original to my '99 DII. It was in its original location under the bonnet until a few months ago.

 

I guess the takeaway is that some get brittle with age and some don't. Ż\_(ツ)_/Ż

 

i'll tell my brittle, broken nylon lines to knock it off and quit being brittle and broken.

 

I'm guessing humid climate vs dry climate played a big role here.
My D2 has its original lines - 02 at 222k miles.
I probably wouldnt tie it in a knot but my D2 came from a similar area as the OP.
Asheville to Florida for the previous owner and I'm in the Spartanburg area, so its always been on the east coast in a high humidity prone climate.

Just my best guess anyway

 

Climate does make a difference, but so does the particular batch of plastic.
My 04(according to Carfax) lived it's life in Ga, Va, then 3 years in Md and Pa...all fairly hot and humid.
That coolant line on mine snapped like a twig, and in as many places as I tried bending it.
Too many variables to nail down exact causes, but material quality and conditions are the big 2.
That line needs to go in a museum, lol.