94 cutlass supreme overheating - please help

I have a 94 cutlass supreme with the 3.1 engine - I replaced the thermostat this evening as I couldn't drive it more than 1 mile without it overheating without any apparent way to bring the temp down without shutting it off for a while.

Initially the car was still overheating after the 3 hour thermostat change (I'm not good with hard to reach bolts) & a short drive. I came back home & searched online for about 2 hours & came to the conclusion that I might have air in the cooling system; I drove the car some & periodically released the bleeder valve near the thermostat - I am still getting some air.

I honestly don't know what I'm doing & I don't know how to go about this:

How do I bleed the cooling system of air successfully? I cannot seem to find a detailed answer.

What the car is doing is this as of now:

I start the car & drive. The heat kicks in, but as the temp gauge goes up, the heat comes down. Before I started bleeding the coolant system there was almost no heat (it was very weak), but as I've spent a couple hours of driving/bleeding the heat has gotten better. When I sit in a parking lot or along side the road (idle) the temp gauge goes up: I then get the car up to 1500-2000 rpm & the temp guage goes down & the heat starts coming back out of the heater.

Only one of the cooling fans work, and both the upper & lower hoses for the radiator are warm (top is hot, bottom warm).

Now I plan on starting the car up & letting it run with the radiator cap off for as long as I can to see if I can get some more air out of the system - but I don't know if I'm going about this correctly & I don't know if these are symptoms of another issue & I'm wasting my time trying to get the air out.

I know that the radiator needs to be flushed; the resivoir is nasty: the contents are more of a thick sludge than anything: though I drove it for quite a while like that before I even bothered to look in the resivoir as it was always at an acceptable level.

If anyone can be of any help, giving me details on how to bleed the system for this motor, or if there's something that I am missing, it would be greatly appreciated.

Thanks.

try taking off your rad cap and allowing the coolant to boil over... rev the engine and watch down the hole, the level should drop as the pump sucks it up. You probably do need to have the system flushed. You should also make sure you use the right coolant for your car. Some coolants will cause the sludging.

Thanks for the response.

I did let the car run with the radiator cap off the other day after posting this.
It seems to have helped immensely; though I am still having intermittent temporary spikes with the car when I am idle.

I plan on getting the sludge removed ASAP & getting the system flushed as I think that would help considerably.

Thanks again for your response on this.

No problem. Your probably getting that spike at idle from reduced flow, so the coolant has more time to sit in the upper passages and heat up. Its important to get it done soon... high fluctuations in temps can cause physical damage to the engine from expansion and contraction.