Career
As a player, Koolhof had a long and productive career, with 190 league goals. He played for a number of clubs in the Netherlands including Vitesse Arnhem, F.C. Groningen and PSV Eindhoven. Foreign the latter he scored a total of 69 goals in 106 appearances and formed a great tandem with Norway"s Hallvar Thoresen in the mid-1980s.
Koolhof is the father of De Graafschap player Dean Koolhof.
He began his career at the local pride BV Veendam, breaking into the first-team squad in 1978. He began scoring prolifically in the late 1980s, attracting a lot of attention.
He was transferred to Vitesse Arnhem in the new decade. In his second season in Arnhem he managed to score 19 goals in 16 appearances, an exceptional average of 1.2 goals per match.
During the 1981/1982 transfer window he signed a contract at PSV Eindhoven, his first Eredivisie club
His first years in the lichtstad (city of light) have been very successful. He adapted quickly to higher level and in two and a half years he missed only a few matches. Then, in 1984 he suffered a terrible injury.
He was out for two full years.
In season 1986/1987 he returned to the pitch but he never fully recovered. He played professional football for another seven years, mainly in the Eerste Divisie.
After Football Club Groningen, again Vitesse Arnhem and De Graafschap he ended his career where it had once started: BV Veendam. He first played for the Netherlands on 14 August 1982 against Greece.
After 46 minutes of football he replaced Piet Wildschut.
He was capped only 5 times, scoring zero goals. As a result, he did not enjoy a long international career: he played his last international match on 16 February 1983, just over 9 months later (in the Euro 84 qualifier against Spain, 1–0 loss). After he quit playing Doetinchem became his new domicile.
He acted alternately as head of the youth academy and manager of De Graafschap from 1994 to 2002.
He was Hennie Spijkerman"s assistant for one season at Football Club Emmen. In the following years he was employed at AGOVV Apeldoorn, Football Club Dordrecht and MVV as manager.
Koolhof was fired from his job on 19 February 2007 due to disappointing results, strikingly on the same day Cambuur Leeuwarden let go their trainer Roy Wesseling. On 15 March the 47-year-old Koolhof signed a two-year contract at South Carolina Cambuur-Leeuwarden taking effect 1 July 2007.
Gerrie Schouwenaar, who acted as interim manager, departed for Qatar.
His spot was taken by Alfons Arts, who became Koolhof"s assistant manager as well as a youth trainer. In his first year his team surprised everyone by defeating Arizona Alkmaar in the Cup (1–0). After a few matches in the 2008–2009 season, Koolhof was sacked following a poor start to the season.