Air and Hard Starts

[JHoffman93]

Ok, as winter is quickly approaching I have noticed more and more guys with trucks that are starting hard, mine included. I have also noticed that it seems that leaking fuel return lines is given as the reason quite often. My question is why are trucks with leaking fuel return lines only hard to start when it's cold out? How come plugging them in for a couple of hours makes them start right up? How come an engine can start right up during the summer months with air in the system but can't when its cold? I'm not doubting the diagnosis, just wondering what makes this true.

[FL-Mudd-Duck]

could be rubber get stiffer in colder temps

[JHoffman93]

Heating the water in the block isn't going to affect the temp of the rubber on top of the engine, at least I would'nt think so.

[Dave Sponaugle]

The rubber shrinks as it gets cold, just like everything else.

So more leaks, or small leaks worse.

Then add in the fact diesels already are harder to start as temps get lower, so the small problems compound into a bigger problem.

Unless you leave the hood up, a warm block will make the return lines warmer than they would be on a cold engine, heat rises.

But I am going to put most of the blame on compounding several small problems into a larger one.

[JHoffman93]

Makes sense I guess. The good thing is there is only a few things that will cause the IDI to not start. Even if you shotgun parts at it there are only a few that cause hard starts. I think mine are the relay and a small leak on the IP for the #7 cyl.