Ok here it is. I installed idiot lites on my GPR just to let me know if relay stops working, and at what ambient air temp it doesn't come on, so far 85+ degree weather it still comes on (they stay on for about 1-2 minutes). But if I drive the truck and the engine is at or around operating temps they don't come on. Is this normal?

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Yep... perfectly normal... The main factor is engine oil temp...

 

if engine oil temp is below 135 degrees, glow plugs should operate