Markerclusterer mouseover not working

I just looked at the following message: markerclusterer info windows

In this article, I need something, a mouseover event for markerclusterer. I need to change the icon when the mouse hovers over the icon.

I got the following code:

var clusterOptions = {
    zoomOnClick: false,
    styles: [{
        url: 'images/template/cluster.png',
        height: 68, 
        width: 57,
        textColor: '#FFF'
    }]
}
var markerClusterer = new MarkerClusterer(map, markers, clusterOptions);

google.maps.event.addListener(markerClusterer, "mouseover", function(cluster) {
    console.log('test');
});

// Listen for a cluster to be clicked
google.maps.event.addListener(markerClusterer, 'clusterclick', function(cluster) {

    var markers = cluster.getMarkers();
    var content = '';
    $.each(markers, function () {
        content += this.get('content');
    });

    // Convert lat/long from cluster object to a usable MVCObject
    var info = new google.maps.MVCObject;
    info.set('position', cluster.center_);

    var infowindow = new google.maps.InfoWindow();
    infowindow.close();
    infowindow.setContent(content);
    infowindow.open(map, info);

});

The cluster works fine, and information is also displayed. It combines all info windows with markers in the cluster.

What am I doing wrong in a mouseover event? I don’t even see console.log!

Thanks in advance