I've seen both suddenly open, suddenly shorted, and odd higher than spec resistances. In all cases, replacing the plug cured the problem. So the answer to your question is yes and yes. I'd varify the measurements, then replace all the plugs that aren't on target (assuming that you have symptoms of a bad plug - if the engine is starting fine, and idling smoothly, don't mess with it!)
I suspect that you know, but for the record - measuring these low resistances is tricky. I think the proper resistance for a glow plug is 0.6 Ohms. If you short the test leads on your VOM, you'll probably get a higher reading than 0.6. I clean both ends of the test leads, then take a base reading by shorting the test leads together, and subtract that reading from the one I get from the glow plug. Your ground connection when measuring the glow plugs can be highly variable unless you use a clip and leave it in the same place for all the plugs. Even then you can rotate it some and get a different reading. I've also slowly replaced all the plugs over a 6 to 12 month period as they die. I don't do that anymore. One dead plug means they all get replaced. Then I'm only under the hood once for the job. On 10/9/05, Luther Gulseth <[EMAIL PROTECTED]> wrote: > Checked the glow plugs on my CD and mom/dad's '85 300D tonight. D > readings were open, 2.6, 2.6, 2.6, 2.6. Ordering a set for that car for > sure. Mine were 3.3, 3.3, 3.3, 5.0, 4.9. Do glow plugs gradually > increase in resistance as they age? Or do they stay the same, then > suddenly short/open out? This is the question I need to have answered. > -- OK Don, KD5NRO Norman, OK '87 300SDL, '81 240D, '78 450SLC The FSM created the Diesel Benz http://www.venganza.org/
