Please do not take what I am about to say as advice! It is simply what I've been doing. 

I have about 10,000 miles on my zetec a oil over the course of about a year and a half. I last pulled the dipstick to check in August, and that was the first time in about six months. 
I even moved this engine from a different Van in that time, and did not change or check the oil while the engine was on the stand. 

The engine has mobile 1 synthetic, and I put a new filter on it sometime last year. I may do that again soon. 

What am I tryin to prove? 
Nothing. 
The last oil analysis I had came back acceptably, and I just don't see the need to baby a $300 engine block. Oil isn't cheap these days, and I really hate changing it. Yes, I actually enjoy changing engines more than I enjoy changing oil  
Am I crazy? Maybe. Please don't tell me if I am though, it will ruin the surprise. 

Your zetec is built well. The bostig sump holds a lot of oil. Modern oil rocks. 

-craig

On Dec 6, 2012, at 1:59 PM, JarrettAnthony Kupcinski <kupcinski@GMAIL.COM> wrote:

> Every 5000 miles/6 months assuming normal operating conditions. 3000 miles for extreme service conditions. The Bostig recommendation matches Ford's.
> 
> -Jarrett K
> 89 Westy powered by Bostig
>> What did the engine manufacturer recommend for the engine when it was new in a factory installation?
>> 
>>> Bostig recommends an oil change every 3 to 5K using synthetic oil. Since