FP gauge at 0, but cold outside
 

I have only had gauges for 6 months. It was a little colder than normal this morning. I started up and no FP reading while idling for 1 minute. I checked and no codes. It was only 35 degrees. Is this normal when cold. I shut truck down and will check later.

Not normal. Verify the guage first. Is the guage mechanical or electronic?

It will take very cold weather to drastically lower the pour point of diesel fuel and much colder still with winter blended fuel in order to have a noticable difference in lift pump performance due to thicker than normal fuel......so, to answer the question: no, your symptom is not normal and not a function of cold weather.

Turn on the key and listen for the LP running.....if you do hear it, pop a fuel line and see if you get fuel.

Fuel Isolator?
 

I had the same problem when it got cold. Found that the fuel isolator was the culprit. Actually it was the connection between the guage and the isolator. I did not fill the line with fluid, just left it air. When it was cold the air volume shrunk causing the diaphram to reach its limit.

To fix, after I got out of panic mode, I just equalized the air volume when it was cold (with the engine and FP off) by disconnecting the guage side connection and then reattaching it.

No problem since.

Scott

Now I'm new to diesels and gauges but I've never heard of running no fluid from an isolator to a guage. How can air actually replicate real fluid pressure?

If you have an isolator I'd just junk it and get a needle valve in it's place. I know it's hard to throw away about $100 but it will solve so many more problems you experience later. I just ditched my isolator suspecting a failing LP and all is normal now. Isolators = [nonono] in my book now.

Good luck.