Second-from-bottom Newcastle followed up a 1-0 win over West Bromwich Albion with a 5-1 defeat by Chelsea last time out and the former England boss said he wanted more fight from his side when they travel to Stoke City later on Wednesday.
"We see fantastic performances from individuals one week and we look capable of beating anyone, then the next week it's the polar opposite and we can lose by five or six goals," McClaren told reporters on Tuesday.
"That inconsistency is a character flaw we have got to put right. We've scored seven goals away, that's the lowest number in the league and it's not good enough.
"We have to start demonstrating character away from home. It's about having courage."
The former Manchester United assistant coach, who has also managed Middlesbrough, Derby County, Twente Enschede, Vfl Wolfsburg and Nottingham Forest, has 12 games to save Newcastle from relegation.
They can move out of the bottom three above Norwich City and Sunderland with a draw at ninth-placed Stoke.