change the oil now.
That 'one cup' of coolant in the oil is about 10% of the total volume, quite a bit of contamination.
Your choice, a $20 oil change or driving with known-bad oil.
Start using Mobil1 oil ($20 a gal at WallyMart) and change it on a 3-4k miles schedule for a few changes. Change the filter too. DO NOT use any kind of oil additive that claims to clean out a motor. Sure, that expensive kerosese will clean things out, but it will do it all at once and that crap floating around has a chance of plugging something else up.
Better to do the cleaning gently, but that just's my opinion. Others favor the Big Bang.
The frequent changes with M1 will loosen and clean out the sludge. Keep an eye on the car for leaks, M1 is so slippery that it will seep through any marginal seals in the engine.
If you don't get any leaks fine. Stay with M1 as long as you can buy it cheaply. If you do get a few leaks keep on with the frequent oil changes and at the end change back to a oil with a seal-swelling formula like the Castrol high-mileage stuff.
Last edited by '98-ESer; 11-14-2006 at 10:50 AM.