98′ International 4900 Check Engine

Ok, so I’ve got a 98′ International 4900 with the DT466E that has 480,000 miles on it. For the past couple months that I’ve been using it at work,it will need anti-freeze every 2 days and oil every two weeks. Well over this past weekend I forgot to plug my engine heater for the weekend and the temp was about 15 degrees. Well, I get work this morning and it cranks put won’t start. Every now and then it would chug but it wouldn’t stay running. Eventually the mechanic got it running but it needed full throttle just to idle he said and was just sounding horrible like popping and loud tapping like it was going to blow. Took about a half hour to warm up and stop smoking from cold and oil. When I pull out of my spot, I go back to park my personal vehicle and notice this giant black oil puddle that’s about an inch thick that was under the truck. The check engine light was on but when I restarted the truck it went away. Well about an hour later I’m going to my first stop and i’m just coasting in neutral and the check engine light comes back on and the engines just slowly and quietly shuts off. Started back up and didn’t have problem until the end of my route, I go on I-95 to get back to the dairy and the light comes on and the truck just doesn’t seem right. It still runs but I refuse to push it to the max like I used to. I think it wants to blow. Also at idle, i’ll hear a rattling/tapping sound coming from the engine cover in the cab below the dash. Goes away at mid RPM but will get really loud at high RPM. Truck doesn’t smoke. Oil pressure fine. Temp is fine. Just want to know what the heck went on this morning with the oil and what could be in the for see able future.