Mine goes blank occasionally...this morning, for instance...
I replaced the sensor last month, but that hasn't fixed the problem (also reads inaccurately).
The display behind the gauge cluster is most likely the problem...trouble is, the replacement is pricey ($200+).
There are several threads about this in the forum. One member mentions that the real problem is a $5 thermistor which can be procured at any local Radio Shack...I might give that a try.
If your friend decides to pull the gauge cluster, make SURE he/she disconnects the battery FIRST! We aren't short on threads about gauge cluster problems that crop up after doing some sort of work back there with everything hot!