My 1990 Lumina won't start hot. It recently had an episode where the alternator killed without the volt light going on, stranding me in an intersection. Anyway, after buying and installing a bad alternator, returning said bad alternator and replacing it with a better one, my car started working properly again. Two weeks later, I stopped to pick a family member up, and when I got back in the car it wouldn't start. I've driven it several times since then, and every time it has problems starting it has been within a few hours of me driving it. I leave it overnight and it starts up again.
I've had one suggestion to check the spark plugs (which I'm going to do today or tomorrow, as soon as I figure out how :) but was wondering if anyone else had any other ideas.

When was the last time the thermostat, temp sensor that turns fan on and coolant was checked? I'd check that first. Cars have an automatic shut off when they get too hot. When they cool down, they run fine again. That happened to an old car of mine and I changed the the stuff mentioned above and never had the problem after that. Just something to check on.

Thanks. Not sure when it was checked last, meaning it's been at least five years (parents owned car before that). Is the thermostat easy to get to, or is it something that a mechanic would be better off looking at?

Follow the top radiator hose from the radiator to its destination. There you should find where the thermostat is located. usually looks like a half round covering held on with 2 bolts. Do it when the car is cooled down.

Right near that you should see a plug (screwed in the engine) with wires comeing out of it. That would be your temp sensor to surn the fan on. It would be a good idea to replace that also. Another easy part to change.

let us know the reults.

i have the same problem, on a 92' LUMINA APV, engine won't start when hot, when it cools down about 45min later it starts... In my car its the fuel pump! the pump may have to push harder when the fuel in the line is hot (it runs in lines that are close to the engine and those lines do get very hot) and expanded, this means the pump (which is in the fuel tank) draws more current, when the fuel in the line is hot and under pressure... The pump draws 4Amps when running and i saw 7Amps locked rotor amps going to the pump when it was hot and the pump would not start up.. I increased voltage to the pump and forced it to start up by increasing the battery voltage, ie the pump starts and runs fine when hot if i feed it say about 18volts - careful this is to the pump only.. - its not wise to do this really as it may burn out the pump - but to just get it started and then let the voltage drop to battery voltage to 12 - 15volts it will keep running...
This is not easy to do if you are a novice with electrical circuitry, so if thats the case and your pumps not starting when hot you may need to replace the pump or have the electrical connections to it checked for high resistance.. You should hear the pump start by turning the key to the point before it cranks the engine, the fuel pump will /should run for a few seconds before you crank.. if you dont hear it turn key off for 5 secs then try again and listen for it whirring.. you'll hear it when cold and it should do it when hot also ... if not its the pump.. I was quoted $250 to put in a new pump... maybe i'll do that.. I've heard the pump can be damaged by running dry so if you've run the lumina out of fuel a few times the pump may have been damaged by that and could cause this problem.. my pump runs fine for hours, and re starts fine if the engine is cool but if engine gets hot, fuel line gets hot, the pump can't start therefore engine can't start till everything cools down.. hope this helps, Colin

This post is to sirdarksol. Drive it for a while, and shut it off next to a car, so it can be boosted easily. When it doesnt start, try boosting it and see what happens. If your alternator went out, you ran the battery down, and as far as they go, once they are really dead, the should get replaced, cause they will never charge too good anymore. More than likely, when leaving the car sit overnight, the battery charges itself up enough to start the engine, strange but happened to me when my alternator light went out in my 1990. Volts light came on, attempted to get home, batt died half way, no crank, nothing, towed it home, then next morning, she started right up, but soon died, because the battery was dead, and alternator was shot. I would defenatly have the batt checked out, and possably the connections, and maybe alternator again. Yes, they can be cheaply made, and die that quickly, I went through 4 or so on one vehicle I had (FORD). I recomend using only factory AC delco, or NAPA parts, no aftermarket crap. Well, good luck, and let us know how it tuns out.