Here is the Coats web link for what is listed for patents:

http://www.coatesengine.com/patents.html

This is the real short answer from WikiPedia:

"The term of a design patent is 14 years, measured from the date the patent is granted. This is in contrast to a utility patent term, which typically lasts 20 years and is measured from the application priority filing date. Design patents are not renewable and require no maintenance fees."

Now we all know patent system is insanely complex, so how the 1990 patents fall into this is not really clear to me.

Are these design patents or Utility patents?

Anyone better versed?

This is the first patent listed on Coates site:

http://www.google.com/patents/US4944261