GeekGurl2000

I bought a 2001 Mustang in June. I have experienced a few issues with it, particularly on hot days. I was working last fall as a Census enumerator, making many short trips (few blocks at a time) The car started to be sluggish, felt like it wasn't firing on all cylinders, and was backfiring a bit. A few stops later, when I tried to leave, it would start but die when i shifted into Drive. I called AAA for a tow. When he got there an hour later, he was able to drive it up the tow bed ramp. Later that night, I was able to drive to the corner market about 6 blocks away. Then, a few days later, I took my roommate downtown to pick up meds, and the car almost overheated on the way back. The AC started to get warm (I'd had Honest 1 top off the refrigerant about a month ago) and then I noticed the needle moving up on the gauge, so we turned off the AC and turned on the heat and were able to get home without a boil-over. I did some checking, and learned that the last owner had put the wrong kind of coolant in. (It's supposed to have the orange DexCool, not the standard green stuff). I've gotten a mix of opinions with about half saying it doesn't matter.
I did replace the thermostat recently as a cheap part that might help. Anyhow, it will start and I can do a trip, like yesterday I drove to Wilsonville. I made the mistake of shutting it off when I got home, then it wouldn't run a few minutes later when we were trying to get to a movie. One time, someone helped me after a stall and he said he had experience with race cars and that it sounded like an "overheating ECU" I am tempted to just get one and replace it as the cost will be about the same as diagnostics. I see some info on how to reset an ECU, but haven't found info on my specific model year. Looking for diagnostic advice. I currently have no income as I'm recovering from cancer surgery and haven't started a new unemployment claim.

Derf00

There are green colored traditional coolants and "universal" green coolants that are supposed to work with all types of coolants. I never use universal fluids for anything. You get extra junk that is not compatible with your vehicle and you don't necessarily know how that new fluid will interact with any old fluid that may be left behind.

Normally I would start with external stuff like cooling fans etc but because the coolant is an automatic unknown, I'd start there.

Get rid of all the incorrect coolant. Drain it, remove the thermostat and put the thermostat housing back on without the thermostat, disconnect the top and bottom hose from the radiator but leave them connected to the engine side, then run a garden hose into the top radiator hose until the bottom hose has clear water going through it..

Do the same for the radiator and put the garden hose into the top inlet and let it run out the bottom until clear. Now refill with a 50/50 mix of coolant and water. You'll be slightly diluted from left over water in the block to like 40coolant/60 water or even 30 coolant/70% water but you'll be fine in Oregon.

Put a new thermostat in it. Now drive it. Problem fixed? Great, if not, now you'll need to dig deeper. Fans coming on when they should? Radiator have good flow or not? They can get clogged from incorrect fluid gelling with the OEM stuff or even accelerating corrosion.

Beyond that, you should check back with what you found or how things to turn out if you need more advice.