Possibly air in the line. Have you bled the filter housing?

I mentioned in the original post that I tried that and it didn't make any difference.

Ah sorry. That's what I get for reading while driving. Are there any codes? What glowplugs do you have?

Ugh.
You guys and your metric system.

What year is your CRD and is it a 2.5L or 2.8L?

Usually, if it's hard to start when hot and it's not an air in fuel problem, it's the crankshaft position sensor.

ok slow down ,,, this is jeep crd you need to be patient with it , first you need to lots of reading , research , etc , this motor and its behaviour can drive you up to no good ,GP system for US market is no good > so we have people that can help with cold starts , just see webasto install procedure . and yes it starts no problem.

By "you guys" you mean the entire world? .. I can talk metric or standard. The year is in the subject and it's a 2.8L. I'm in Canada if that helps. If you read my original post it starts good when hot and better when cold and not so well around 40-50F.

Thanks. That helps a lot.

So it starts good when hot and cold?
But somewhere in between hot and cold it doesn't?

I think it's a fuel system problem.
Either air in fuel or you need a new fuel filter.
But check all your electrical connectors. Maybe you have a intermittent loose connection somewhere.

BTW, I live in Florida where 20C is a bit chilly

Sounds like it might just be a bad battery then.
Wouldn't hurt to get it tested.

If you switched from Celsius to Fahrenheit, it should start easier.

I'm a big fan of the Racor 245 fuel head with an inline Kennedy lift pump to eliminate air in system.

I had glow plugs go bad on me without a check engine light being illuminated. If your glow plugs are 3-4 years old, they may be weak.

I never got a battery to last longer than 3 years. Battery would be fine until it started getting cooler and starts became harder. This is despite driving mostly highway for at least an hour each way to/from work.

Do you know what glow plug system exists in your vehicle? Such as 5V vs 7V, and if 7V which system?

Some have mentioned the "upgraded" Bosch steel 5v system is uniquely odd since they have Lower operating temps, higher current requirements, and less effective heated surface area than either of the 7V systems. Also the ecu programming may have variable 1-0-1-0 cycle duration depending on ambient temperature, which could explain why it starts better at or below freezing.

I mentioned in the original post that I had it tested and it was 80% of 850CCA, actually it was closer to 85% it was 728CCA does anyone know if that's good enough? And again, why would it start when freezing if it was the battery unless the CRD has some different starting method electrically at different temps.

If it starts easier with the booster then it would seem that the problem is battery. Right?

Actually, none of your symptoms make any sense. So who knows.

The glow plugs turn on every time you turn the key on to start the engine. How long they stay on depends on how cold it is. But if its warm enough you can unplug the glow plugs and the engine will still start.