Long story as short as possible. I had a 98 navigator with a cracked radiator. I used some jb weld silicone as a temp fix but it was cracked beyond where I could reach so I finally got a backyard mechanic to swap it out (new radiator purchased on Amazon). It never overheated, as soon as it would start getting hot, we’d pull over and get some water in it As soon as he was finished swapping the radiator, we drove it around the block and the idle was rough and the car was bogging. Drove it about 15 miles to work and it started misfiring (cylinder 4). Got it home, tried to go to work once more today and it continued to misfire and just in general have a rough ride, but then also began getting hot.
Is it possible something wasn’t done correctly when the radiator was put in? We didn’t replace the thermostat because it hadn’t come in in time. Could that be affecting anything? It’s strange because with the cracked radiator, it was driving completely fine aside from the leak, and right after changing it, we’ve had issue after issue. What could be causing it?
I think that this engine is coil-over. I would check that the coil or the injector were not accidently unplugged when the radiator was replaced. Sometimes it is easy for a mechanic to accidentally bump a wire and unplug it in the process of doing a repair.
My first thought as well. Engine got hot, head gasket blew or head cracked, the new radiator upped the coolant pressure enough to force coolant through the crack into the combustion chamber. I could be way off base, and hope that I am.
My dad has an f150 with the 5.4 liter V8. There’s a crossover tube (coolant passage) on the plastic intake manifold that cracked. It would cause his engine to misfire by spraying coolant onto one of the coils / plugs. This engine in the Navigator might be similar. I could see the new radiator causing more coolant pressure, forcing more coolant through that crack in the intake as a possible scenario.
Good luck op. I’m just spitballing here. Hard to tell without looking at the engine.
Maybe swap coils with another cylinder, just to rule out a bad coil or plug. If the misfire moves to another cylinder, you’ve found your problem. Pull the plug on the missfiring cylinder also. See if it shows signs of coolant.
Replacing a radiator isn’t that big of a job on many cars. No experience w/the Navigator tho. But I’m guessing whatever the problem is happened before the radiator replacement.