Can you use 25w50 oil instead of sae30 oil?

No.

First the viscosity is wrong. SAE 30 is a single-grade motor oil. The 30 is a designation of the oil's viscosity grade according to the SAE. The 25W-50 is a multi-grade motor oil, meaning 25 grade viscosity in Winter (hence the "W") and 50 grade viscosity in normal operating conditions. If you wanted to match a multi-grade motor oil in viscosity to a SAE-30 grade oil, then you would need a multi-grade oil that had ended in 30, for example 10W-30.

Second, if you have been using a single-grade motor oil, you should not switch to a multi-grade because most single-grade motor oils do not have the detergent additives found in multi-grades. Switching to a multi-grade with a detergent present could suddenly dislodge gunk deposits creating a problem with solids and significantly decreased lubricant performance.

Now, with all that being said, if you drive a really old diesel truck and change your oil constantly, then the 25W-50 would probably be a great choice. Since the extreme pressure and heat in old vehicles tends to thins the oil, the high viscosity is probably helpful. And, if you change the oil often, the detergent will do you more good then bad.