Heat Rave R

As many of you may know, the 280ZX turbos had a combination oil pressure/oil temp gauge in the same housing. On both my turbo cars, the oil temp needle has never moved on either of them ever since I bought them (the oil pressure part works fine on both). And one of them is practically brand new at only 86k miles old! Does anyone have any idea what the problem might be? Bad sender? Is this a common problem on the turbos or am I just having bad luck?