my Bobcat ct335 doesn't start when outside temperature is below 50 degrees.

[Bowhunter32]

When the outside temp is above 50+ degrees, tractor starts fine. below that temp, it just spins no ignition. already changed glowplug relay. any suggestions?

 

[seville009]

Check your battery.

Under 50 degrees is not very cold, so there shouldn’t be any gelling or other cold weather related issues.

All of your fluids clean and full (oil, fuels, hydraulic)?

 

[DK35vince]

Still sounds like a glow plug issue.
Have you tested for power at the glow plugs ?

 

[WranglerX]

Check voltage to glow plugs, and check glow plugs to see if they are shorted or open.....

 

[CliffordK]

I agree that it sounds like a glowplug issue.
Depending on where you are, 50 degree days may be few and far between this time of year.
On my old Ford when I was having troubles with cold weather starting several years ago I stuck either a hair dryer or heat gun into air intake, and it helped it start. At least a way to get it running. I don't remember if I replaced any glow plugs, but the glow plug indicator seemed to be wired in series with the glow plugs, and had a wire that had burnt in half.