05 3.7L 115,000miles. When I start it doesn't seem like all cylinders fire. When I do get it started all the way I get a pretty loud popping noise coming from the top center of the motor about every 5-10 seconds.
Above the water pump to the right there's a fill plug where the radiator hose attaches. It a recessed Allen head I believe. Back that out, put a funnel in the hole and fill with coolant, then install the plug.
After that I believe you're supposed to cycle the engine on and off a few times with the radiator cap off. Just let it run a few minutes to warm up to then shut it down. As it cools it should syphon some fluid from the reservoir. Do that 2 or 3 times, put the cap back on, top off the reservoir and you should be good.
It's a sealed system, you need to get all the air out of the lines.
I was loosing coolant which is how I noticed water pump leak. But motor only seems to not fire all the way when I refill coolant. Some white smoke but not a huge cloud. The code it read before I did water pump when it wouldn't start all the way was misfire cylinder 5.
Old school test is while the engine is running, put you hand near the end of the exhaust pipe so the exhuast blows on your hand. (not close enough to burn your hand) for say 5 seconds, then smell your hand. if it smells sweet you are burning anti-freeze.
If you are burning anti-freeze then likely head gasket, and you'll be preasure testing it to find the exact-cause.
A miss fire could be just a sticky injector? replace the injector "if the code keeps showing up".
It really depends on the "popping sound". If you are not sure.. don't drive it. I saw a guy one time drive a truck with a small ticking sound... 2 miles later dropped a valve, and cost him $2000+ in parts. vs. all he really needed was a valve clip.