I have a '89 full size 5.7, 4wd, 4spd tranny with O.D. (700R4), EFI. I've never had any problems with it aside from starting it in the morning when the temperature is below 0 degrees F.

I was driving on the highway at about 50mph when the engine just cut out. After checking under the hood I found a loose ground-wire and tightened it but the engine still would not start. Accessories came on, so I was getting electricity but the engine wouldn't turn.

After I got it home I eventually tried to turn the crankshaft with a breaker bar but it was stuck. I checked the oil and the dipstick was bare. I had checked the oil level only a few days ago and it was fine. I didn't see any signs of leaking nor was I burning any oil.

I have two questions. Is my engine seized and if so, where did my oil go?

 

I would say check your battery connections again. Terminals and at the starter, Then make sure battery is good and charged, Does it even click when you attempt?

305's and 350's are notorious for leaking oil out of the back of the intake manifold, behind the distributor. It will run down the bell housing, and you'll think its the rear main. You need to get up under it and look. Any work done lately to it? Higher mileage chevy v8s also like to **** oil out of the timing cover seal, Those are the heavy leak areas. Drain the pan and see if there is any oil left. How hard are you trying to turn it over? Are you sure the battery is not dead and the terminals are tight and clean? If you can't budge it all thats not a good sign.

 

The mileage is slightly over 87k. I've not had any work done since the last oil and spark plug change.

I just cleaned the terminals and replaced the cables, which are tight but I did have a loose ground. I can hear the ignition engage when I start it but the crank isn't turning at all. I haven't checked the back of the manifold but I haven't had any oil spots on my car port.

I'm thinking I spun a bearing or maybe worse.

 

Sometimes you may think they are tight, but that will still cause a no crank situation. They also have to be clean. Clean the terminals on the battery. Scrape the grime off so you can have some clean metal contact. You say the cables are new, so the cable terminals should be ok. Also make sure battery is charged! But you've probably went over all this.

Very possible if you ran the oil low enough, that there could be cam bearing/cam, spun crank/main bearing.

Drain the oil and see how much is left. Also look for shavings.