Engine blew about a quart of oil out.
 

I drove about 600 miles this weekend pulling a UHaul trailer with a car on it. I was cruising along about 65, looked down and I had no oil pressure. Hot the brake and the auge jumped right up. But, every time I ave it more fuel it started to drop. The gauge would move around when I was driving 60. I stopped at the next rest stop and checked the oil and it was down about 1/2 way between add and full. I stopped at the next town and put a quart in and it never did it again and I drove 65+. What would make it blown oil out of the vent hose under the truck? I noticed that the oil pressure light did not come on at all and it does work. I figured the gauge may be jumping around because something may be plugging the hole, but that's a guess.

When I killed a Head gasket on my vw, the compression pushed oil out the dipstick... not sure about your CTD- maybe a bad turbo? Others will most certainly chime in soon.
There is a chance that your sending unit just went crazy, and your truck was 1 quart low before you left that day?

First off, I wouldn't get excited about a quart low.

It is probably the oil pressure sending unit getting flaky. Get one from Cummins and replace it.

Patdaly,

That's what I was figuring after it dawned on me that the oil light was not coming on.

Bob