Having in mind what i read about the Coulthards (and Coltharts, etc), that they're probably from a French village called Coutherde or Couherde, i've looked at Google.com and found this:
Spouse: de Fiennes, William {I16691}
b. ABT. 1240 Wendover, Buckinghamshire
d. 11 JUL 1302 Battle of
Coutrain , West Flanders
Gender: Male
Apparently there's a Belgian village in the province of West-Flanders called Coutrain. Maybe a thought, though nothing confirms my idea, but to be precise i couldn't find any idea about Coltrane, except for one babyname site saying it was a version of Colt (yeah, sure, and where does the ending suddenly come from?). Never trust babyname sites, mind you.
Another, different Coutrain:
+ Deneau, Rene b. ABT. 1662 Coutrain, La Ferte Gauche, Champagne, France - d. ABT. 1707 - Marriage: 1667 Beaubassin, Acadia, (Amherst, Nova Soctia)
And another:
ID: I333878
* Name: Blanche De Brienne
* Sex: F
* Birth: ABT 1240 in Coutrain, Mynn, France
* Death: 1302
* Reference Number: 333878
Same person with her husband, who died in the Battle of Courtain:
260057790. William De Fiennes was born in 1245 in Wendover, Buckinghamshire, England. He died on 11 Jul 1302 in Battle Of Coutrain, Flandre, Occidental, Belgium. He married Blanche De Brienne in 1269 in Wigmore, Herefordshire, England. [Parents]
260057791. Blanche De Brienne was born in Courtrain, Mynn, France. She died in 1302. [Parents]
Important note: see how in this case the Coutrain changed into Courtrain?
Coutrain is a surname in this database:
www.escndatabase.com/c.htm i found out that Coutrain, Mynn is Courtrain, Mayenne, France
now i've found out that the Battle of Coutrain is the Battle of Coutrai. Coutrai is the French name of Kortrijk, a Belgian city. In a way, those old genealogy registers where under influence of changes regarding names.
To add, i've found that Coutrane is a surname as well
and: Coutrain, La Ferte Gauche, Champagne, France is better known (more hits) as Coutran, La Ferte Gauche, Champagne, France
[...Généralités Historiques :
Mentionné au 14ème. Siège d'une commanderie des templiers (Coutran), puis des hospitaliers. Eglise à la collation de l'évêque de Meaux. Prieuré bénédictin de la Maison-Dieu.
Architecture civile :
Restes de la commanderie de Coutran : logis du commandeur, chapelle* 13ème à voûtes d'ogives et culs-de-lampe sculptés, tourelle d'angle carrée. Moulin à eau....]
Historical generalities:
Mentioned in the 14th [century]. Seat of a commandership of the templars (Coutran), later of the Knight Hospitalers. Church "à la collation" of the Bishop of Meaux. Benedictan priory of the Maison-Dieu.
Civil architecture:
Rests of the commandership of Coutran: house of the commander, chapel of the 13th century "à voûtes d'ogives et culs-de-lampe sculptés, tourelle d'angle carrée". Watermill.
Apparently not a placename, but the name of a commandership of Templars in La Ferté-Gaucher.
Now i've found out that
courtraine is the adjective of Courtrai, i.e. means 'of Coutrai' or 'from Coutrai', like Roman and Rome and Moscovite and Moscow, etc.
Someone with the surname Courtraine would be from Courtrai (Kortrijk) and this surname could have changed through time in England to Coltrane (like Coutherde and Colthard).
Still this is all just guessing and possibilities