I have a 08 megacab with the 5.7 that ive owned about a month. And now I’m battling water temp problems, at first the temp was varying between 208-221 then the fan would kick on and it would cool back down, so I replaced the thermostat, and that fixed it ( or so I thought), temp would stay between 208-210 but I just got back from a camping trip, and if I give it any excessive throttle it climbs up to 221 rapidly. Or just cruising at freeway speeds, it will hover between 213-218. I just replaced the fan clutch and that didn’t help, if anything it made it worse because the new fan clutch won’t disengage so it’s always on. I’m lost with this, thermostat again? Water pump? Radiator? All of the above? Thanks for any help

Do you smell coolant outside of the truck? I also have an 08 5.7. If I had my windows down at a stop light, or once I got out I could smell coolant. Never overheated, but I had a small coolant leak coming from the radiator. Also found that the wrong coolant had been put into the truck. Once I replaced the coolant and the radiator, the truck ran dramatically cooler. Super easy to replace. Hope this helps. Sounds frustrating.

I can smell coolant outside the truck, when it gets in the upper 220s, I just replaced the water pump and thermostat again and put in a new radiator, and it still gets hot, average is 213-217 on the freeway at 80 mph if I give it a little for throttle to get up to 90mph it will peak up to 224ish. I’m completely stumped..

I flushed out the heater core when I did the water pump and flow looked good same flow as was coming out of the hose, I’m leaning towards fan clutch, I’m going to put a 180 thermostat in tonight and see how it runs with that in, we have terribly cold winters where I’m from so if it runs okay with the 180 thermostat in for summer I can put the 203 Tstat in for winter and keep it warm. I will update and see how that goes, if the 180 don’t work it’s going to the dealer

Well put a 180 tstat in and it holds my temp around 197 on the freeway 188 in town, I’m content with that, pretty sure the fan clutch is my problem, think I’m going to go a Efan route so I can adjust the temp times on when the fan comes on