I have an old deep fryer, I bought at a garage sale, I pour the oil in there, just to warm it up. It thins it just enough to spray easily, and it spreads better, because it's warm/hot.

Is it dripless oil spray? I used to thin that with varsol.

JMO, but i'd try warming it up also.

Back in Finland they sold two different types of undercoating materials, first one which was meant for spraying was fairly thick stuff (compared to thick primary paint) but still clearly fluid and came out of the undercoating gun just fine and no thinning was needed, the other one was for brushing and really thick and close to body filler thickness.