About 10 days ago the coolant reservoir on my wife's girlfriend's 2008 X5 3,0 si had a crack about 5 inches long. I replaced the reservoir a week ago. Now the engine overheats. I applied the failed-WP-confirmation procedure that killcrap had outlined in post #6. In my case, the flow of coolant to the reservoir is pulsed, not a constant-flow, and I can hear the pulsed coolant movement in hoses with noise of "air bubble sputtering."

What does this pulsed coolant flow back to the reservoir mean? Is the WP working or not? If the WP is working, then the overheating is caused by a stuck-close t-stat, right?