2006 Nissan Altima 2.5 S. 166k. Starts great when its cold. Hard starts when its warm or hot after sitting 15-20 minutes. For example I start the car in the morning. Drive to the grocery store. When I come out 20 mins, 1/2 hour later it doesn't want to start. Cranks for a good 15-20 seconds then starts. No codes. Battery, alternator, starter are ok. Replaced crank sensor, cam shaft sensor with OEM. Recently replaced the water pump, both thermostats, temp sensor, all the coolant. Not going through any coolant or oil since I started driving it 300 miles ago. Just seems like when the engine warms ups, doesn't want to start and I may get stranded. I'm not sure what to do next, would appreciate any help.