Overheating
Going through the same thing with my 2000 2.7 l intrepid.
Thermostat, water pump, plugged radiator, blown head gasket? I tinker with autos, but on a very basic level.
My story and course of action (that you may be able to glean some ideas from)
I live in NW Indiana, and was on vacation on ease coast. Noticed water/antifreeze leaking from vehicle in a New Jersey Rest stop. Don't believe car was overheating at the time, but possible that I drove the car for up to a mile in this state.
Had vehicle towed to a local garage (Friday afternoon, so thought garage and not dealer was best option for geting back on the road asap).
Garage diagnosed water pump, and replaced it ($750 US). Said there was some antifreeze in oil, so engine flushed oil system, coolant, replaced oil filter, and refilled oil and coolant.
Car operated fine for 1 week of pretty hard driving (both local and highway driving, and then rather large hills in Maine). Then on way home, near Erie PA, car overheated on Toolway. Noticed overheating pretty quickly, within 1/2 mile.
Towed off of tollway, where refilled Coolant (added about a quart). Drove car around local town for 10 - 15 minutes, with no problems. No sweet smell from tailpipe (that would indicate possible head gasket leak), no antifreeze apparent on oil dipstick, and no visible coolant leak on or under engine, so drove on US 20 into Erie, going both 35 mph ;local, and 55 mph between-town driving. No problems. Stopped at place to eat in Erie, gave car a chance to cool down to check coolant levels. No leaks (external anyways) and coolant level where I left it.
Started again, and after approx. 3 - 4 miles of driving, car overheated (almost instantaneous going from normal temp to overheating (noticed it within a block). Overheated 1 block from Dodge dealer on Sun. afternoon. Let car cool down, ensured coolant full, and drove to hotel 2 miles away for night (no problems with overheating, but car may not have gotten back up to temp in those 2 miles- was approx 65 Deg Far ambient. Noticed that when the car does "act up" and heads for overheating, the vents blow cold, even though set for high heat.
Got to Dodge dealer the next morning. Dealer said no external leaks, and no mixing of oil and antifreeze (mixing could indicate blown head gasket). Diagnosed thermostat ($340 for parts and labor), and would be fixed in 3.5 hours. 8 hours later, dealer said finally had thermostat changed, but still overheating. Would try to reblead air out of the cooling system (air or air pockets in the system could cause overheating). Still no luck - car was overheating. So dealer said next thought would be partially plugged radiator. Plan- next morning, send radiator out for testing.
Well, radiator was sent out, and some gunk was found and cleaned from radiator
($225 US), but dealer said was not enough to be causing the problems I was getting. Next guess was to check the water pump, at $700 -$800 labor to see if it was defective. Dealer said, but I have not confirmed, that car would idle fine for unlimited time without overheating, but when took out for drive, it would overheat. The cooling fan was functioning properly.
Well, at that stage, decided to just tow car home, and fix there so I rented UHAUL truck and tow dolly ($350 US), plus the gas such a vehicle consumes.
Take to NW Indiana garage, and they say,
check water pump to see if defective ($650), replace water pump if defective, and if not defective, pull heads to inspect for blown head gasket (an additional $450 labor). Said exhause gases could be internally leaking into the coolant (because bad head gasket) and causing the car to overheat. Said may consider just putting in a used engine- may be cheaper. Well I know the previous owner, and the car was maticulously kept, so I say I need to think it over. Drove car home (about 2 miles) and coolant temp gage didn't budge an inch- coolant level was fine, so who knows what happened to it...
Checked from garage that replaced the water pump, and said it was a dealership new waterpump that was installed, with all new gaskets, and did NOT replace timing chain.
Go and talk to dad (aren't dad's great!). Dad has rebuild many motors in his day- was a millright who completly rebuilt from scratch Model A's , 1940's sedans, and some cars in the 1970s and 1980s. Successfully rebuilt 2 automatic transmissions in the 70s and 80s as well. Dad's getting up in age (mid seventies) so didn't want to burdeon him, just wanted his input. He said, consider water pump, but he seemed to remember a test you could do on the coolant to check for exhaust gases. After trips to 4 local Auto parts stores (some "fake" ones like Autozone, and a couple real ones), found a guy who knew of the test, and ordered one for me. So, for $40, hopefully will be able to see if there are exhaust gases in the coolant, indicating a blown head gasket.
Will have to make some decisions based on test results. Have about $1600 or so in car already. May try to do work myself- who knows!
Just trying to explain my overheating issues, and giving some insight into potential causes, and remedies that were explored in my case so they may be of help with you.