Mechanical temp gauges do use a capillary tube. Fuel level, by nature, needs to be an electrical gauge, but it's a relatively unimportant gauge anyway, same for the ammeter or voltmeter. I just don't want to trust the important things like
oil pressure and temp to a gauge that needs voltage to work right. Mechanical
oil pressure gauges sweep quicker than the electrical counterparts, so long as the pressure line is -3 or -4 with full sweep elbow fittings. Maybe I am superstitious or just biased, but there are more things that can go wrong with an electrical
oil pressure gauge setup than a mechanical one, and still appear to be fine. If the impedence of the sender wire changes, the connector loosens slightly, you have a charging problem and the volts go out of the range of what the gauge prefers, the sender/transducer goes out of calibration, etc. I have replaced only a couple of faulty mechanical oil pressure gauges in my life, but dozens of electrical gauge senders and gauges. My oil pressure gauge needle move more quickly than my tach needle. Electric speedo's are nice however.