By George Mills (February, 1997)
Don't you just love the gauges in the P1800? Not the late model black faces, but the big, protruding, chrome-bezeled Smiths gauges with the blue faces? My mom, seeing them for the first time in 1984, said laughingly, "Oh, how futuristic!" Love them or not, many a P1800 owner has had to live with them, and that often means cleaning and repairing them.
When you go to take them apart, you discover that the old Smiths gauges were not made to be repaired, ever. The only way to open the gauge is to bend the back edge of the chrome bezel outward so the bezel can be removed. In doing so, you can only permanently distort the back edge, making it difficult or impossible to return the gauge to original condition. And, of course, the gauges are not available new from Volvo any more.
Given the problem, you have to decide whether it's form or function that is more important if a gauge doesn't work right. I always go for function. If you ride in my car, you will notice that all the gauges work (except the clock -- I wear a wrist watch), but if you look closely, you will also see that most of them have been opened at one time or another.
The last one I opened was the water and oil temperature gauge. On this one, the bezel does not wrap completely around in back as it does on the tachometer and speedometer. Instead, the back edge of the bezel is cut off at the dashboard, except for six tabs that bend around the back of the gauge. I can tell you from experience that the tabs will only bend out and in one time without breaking. If you don't fix this gauge right the first time, you will have to create a new means of keeping it together the next time you take it apart.
My solution was to cut a set of elongated tabs out of sheet steel and tape them to the inside of the bezel with duct tape. If I'd had more time, I might have also glued the tabs before taping them. At least the gauge is solidly together until the next time it malfunctions.
The problem this time was that the water temperature gauge always read about forty degrees higher than the actual temperature of the engine coolant. Another P1800 owner had told me the gauge was adjustable, so I opened it up to figure out how.
The mechanism is simple. The part you see from the driver's seat, the yellow thermometer, is really a piece of cloth tape painted black at one end and yellow at the other. The tape is wrapped around two spools just beyond the top and bottom of the aperture through which the driver views it. The spools are driven by brass gears which are moved by a horseshoe-shaped piece of wire. This wire is attached to a curved strip of metal that is moved by pressure from the capillary tube coming from the engine. To adjust the gauge, you simply bend the horseshoe-shaped wire until the yellow part of the tape is where you want it.
The easiest way to calibrate the gauge is to remove the temperature sensor from the engine cylinder head and immerse it in a tub of hot water. (Drain a quart or two of coolant from the radiator before removing the sensor.) Also place a thermometer in the water, and you'll be able to see what the gauge should be reading.
Your mom might be able to supply a candy thermometer for this purpose. Just don't tell her you're using it to fix your car's futuristic temperature gauge.