What do you think is wrong with my truck?

I've a 2000 Ford Ranger and today for the first time it gave me trouble starting up. I had to crank it like three times before it actually started. The check engine light is on but I put coolant(and water) in it yesterday so it's not the coolant

There are dozens of things that can cause an engine to not start on the first or second crank - including simply not holding the key in the "start" position long enough.

There are also dozens of things that can cause a check engine light to come on. Most auto-part stores will loan you the scanner to check the codes yourself. The code doesn't always tell you exactly what's wrong, but it at least tells you which sensor is sending the fault code so you know where to start.

Don't guess, take it to an auto parts store that does free scans. The CEL (Check Engine Light) is one for a reason, and the system is self-diagnosing. The reason for the CEL being on will show up when the scan tool is connected.

No need to guess as to fuel / electrical / etc when the problem is there ready to be read.

Lack of coolant won't keep it from starting- so, no, it's not the coolant. You are quite the trouble shooter aren't you?

#1. Change the fuel filter first.

#2. Take the truck to a Ford Dealer and ask them to test the fuel pressure on the fuel rail pressure fitting beside the fuel injector nozzles. This is a very inexpensive test BUT the fuel filter must be clean to get an accurate fuel pressure reading.

#3. Remove and clean the idle air control valve on-top of the intake manifold.

#4. If the cooling system was low, take the trick to a Ford Dealer and ask then to do an inexpensive 8cooling system pressure test which will find any external or internal cooling system leaks

So many reasons. For that light. Pull codes and go with that info.