Hi,
Past 10 days or so our 1996 5.8 E-350 doesn't start in cold weather, cranks but doesn't even try to start, issue is, it's just doing that sometimes (twice)
recently I started it at -8 weather with no problem, but yesterday it didn't start at 8 above, started and ran fine, but only for about a second, then it's a crank but no start, all it takes to get it started Is a couple hours of garage parking and it starts perfectly! Any body know what the problem could possibly be?

 

There is a big difference between what is the problem and what it could be.
It could be ;
battery not supplying sufficient power to crank the engine plus power the rest of the system.
What kind of maintenance has been done up till now
contaminated fuel that requires hotter spark to ignite
Engine internal condition, wear, low compression
Insufficient fuel supply when cold
Can you tell us what kind of maintenance has been done and it may help to offer some suggestions that might be helpful.
What is the present mileage on the vehicle ?

 

Well I changed the plugs, rotor cap on distributer, new wires, new high output interstate battery, changed the fuel filter bout half a year ago,
Contaminated gas could be an issue, I filled fuel and its been doing that since then, I poured in a bottle of heet, will check how it's running, personally I think it's starting a little more aggressive, as in its idling a little higher right after starting.. Maybe that was my problem.
Not sure about engine condition, doesn't overheat, runs smooth, no misfires and no stumbling, also haa pretty good power and fuel mileage ain't that bad.

 

Looks like you covered most of the bases.
If there is a possibility of water in the fuel, it has a pretty good size filter, but if there is frozen water in the filter it could reduce fuel flow. I believe the tank holds approx 30+ gallons and it may require more than one bottle of HEET to do the trick. Make sure you use only the HEET with the Isopropyl and not the one containing Methanol.
Also, the IPA will not melt ice and for it to do it's job the temp has to go above freezing.