I have a 91 and the check engine light is on, they wont let me smog it with the light on, has anyone else had this problem? please help

Hi, I went to get an oil change the other day and the serviceman said I was missing 1.qt of oil. I went home and put in the synthetic oil that I had. Everything was fine, until I came back from a trip. I started driving yesterday and pulled over to get my sister stuff and then while my car was on the coolant started to leak out underneath the car ( the car started to smoke and it looked like it was just burning coolant?). The car started to overheat after that, I then pulled over and put more coolant in. The car continued to heat up and the coolant started to bubble when I checked the lid. It happened one more time that day until I refilled all of the coolant. Everything was fine until the car started to overheat (no smoke yet) and then the cars check engine light turned on after 5 minutes of driving. I picked up my girlfriend and pulled over and then waited for it to cool down. Then after 10-20 minutes I started it up and it was fine for about 5-10 minutes in which it did it again. Luckily I was close to home so I just went home and parked my car. I've heard from 3 different people 3 different things.

The previous owner: It needs an oil change
source/credibility: previous owner/but no mechanic skills.

Friend in Auto Mechanical school: It's the thermostat or the coolant reservoir.
Source/credibility: Going to school for it/ and teachers advise that the problem over the phone.

Neighbor/dad: It's the water pump.
Source/Credibility: previous mechanics and plane mechanic.

Myself: It's probably it not having an oil change in 2000+ miles despite being filled up with new oil which is causing the engine to overheat and thus burning through the coolant as such.
Source/Credibility: Electrical Engineering student intuition (not much).

i just bought it

I have just bought this 1990 235 canbrio as a project, she has been standing idle for 5 years and had a busted clutch. Privious owner could not afford to fix it. Everthing sticks! I am trying to drop the hood but cannot open the storage compaetment. The little lever hasbroken. I do not have a manual yet, on order, any help thankfully recieved

new clutch is smooth take up good, ist gear good change up to 2nd, crunch! bang lever hard seems to engage 2nd better, all other gears OK

what is the procedure to remove the differentail

A battery cable came undone and now I need to enter a code to make the stereo work again. I know I need the serial number on the back of the stereo in order to retrieve the code. How do I remove the stereo?

Windshield wipers don't work and radio what should I do

Don't know how much more to add other than what was told, its' an electrical problem. Work has been done, but the car hasn't been driven as of yet.

Ran fine yesterday, today won't start. Has husband baffled.

Hi, this only happens when the radio is on (ofcourse). Any action which utilizes current, such as stepping on the break which means the break light turns on, using a turn signal,turning on wipers gives me an audible "poof" like sound to eminate from the rear speakers. Clearly it must be the sound system (it is the original one) but I don't know where to start. Has anyone experienced this before and do you have any suggestions on where to start. I don't want to install a new radio since, once it's on, there is no problem with the sound...
Thanks in advance!

The car has 314000 miles and it runs great.