View single post by Mark Rosenbaum
 Posted: 08-14-2005 05:22 pm
PM Quote Reply Full Topic
Mark Rosenbaum

Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
I've attached a composite photo showing the stock JH gauge on the left and a couple of alternatives that might suit.  The case diameter for most Smiths small gauges, including those used in the JH, is specified as 51.4mm to 52.0mm.

You can install a gauge purchased from a wrecking yard, swap meet, or via eBay, and hope it works correctly.  As an alternative, since the internal parts of most Smiths gauges are interchangeable, you could find a (defective?) gauge with a suitable faceplate and swap the faceplate into your original gauge. 

That said, the presence of numbers on a faceplate does not make a gauge more accurate.  For any particular temperature, the needle's position will depend on the gauge's present adjustment, the behavior of the temp sensor, the output of the voltage stabilizer that powers the gauge, and even the air temperature near the gauge.  If these are all perfectly nominal, the mid-range indication should occur somewhere between 180^F and 195^F, while the red zone should start somewhere between 212^F and 240^F depending on the car manufacturer's desires.  For any particular gauge, the only way to know what an indication means is to use a calibrated thermometer and actually measure the coolant temperature. 

Finally, when overheating is a concern, what matters most is the temperature at which the coolant starts to boil.  This depends on the percentage of antifreeze in the coolant, the (absolute) current air pressure, and the (relative) pressure at which the radiator cap will start to open. You'd have to look up the figures for your specific set of conditions but as a rule of thumb can generally presume this to be 230^F or more.


Attachment: comparison.jpg (Downloaded 64 times)