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#1
09-07-2003, 11:33 AM
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240d glow plug ohms
I see from searching that you should get .5-.8 ohms on each glow plug. Mine show only .3. Are they goners?
__________________
1991 350 SDL 183,000 miles 1982 240D 130,000 miles 
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#2
09-07-2003, 12:14 PM
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Chris,
First you must tell us if you have series or parallel GP. MB Diesels used both types. P E H
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#3
09-07-2003, 12:58 PM
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Probably going to be parallel if they are in the 1983 in his signature.
If that is the case, you are probably OK given the limitations of accuracy in many ohm meters. The better test is current draw, but you need an ohm meter / amp meter capable of handling 20 Amps. If memory serves they draw nearly 20 amps at the start and then settle down to about 10 amps or so when heated up. If they draw under 5 amps, for example, then they are bad. I've had glow plugs that had the right resistance reading, but would not draw the correct current (and thus would not heat properly). The really crude and dangerous test is to hold them with vise grips and apply power to them (parallel plugs ONLY) directly from a car battery. They should glow pretty bright red within two seconds. But you stand the chance of burning yourself badly if you should touch the glow plug. And of course you have to take them out of the car - but no ohm / amp meter required. Ken300D
__________________
-------------------------- 1982 300D at 351K miles 1984 300SD at 217K miles 1987 300D at 370K miles
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#4
09-07-2003, 01:36 PM
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Ken,
I beleive they are paralell if there are four leads on the relay plug. Will a clamp on style amp meter work?
__________________
1991 350 SDL 183,000 miles 1982 240D 130,000 miles
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#5
09-07-2003, 05:57 PM
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Chris, don't mean to hi-jack your thread but I'm in the same situation. Car starts slow when cold...my 240D has the fast glow plugs. They are wired with a jumper between each GP. Out of the car, myohm reading were in the .6 to .8 range. I also had them out and tried connecting to jumper cables, The tip and a quarter of an inch back from it glowed red. I also checked them while on the car...I cycled the GPs and tested the volts of each one and they all were about 10.8 volts and went to zero when the relay cycled off. I am assuming that my GPs are fine and my cold start problem lies elsewhere to be discussed in a separate thread. Am I right in my good GP assumption and testing process?
__________________
Whoever dies with the most toys......Wins! 1984 300d 165k miles
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#6
09-07-2003, 07:29 PM
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Chris,
The resistance is a little low but it might be your ohmeter is a little off. And what you measure id the cold resistance which changes drastically when the GP get hot. Since they all read about the same, the possibility that they are all bad is negligible. Usually when the GP go bad they are an open circuit and very easy to detect. I don't know if a clamp on ammeter will work on DC. I think they work on an inductance principle similar to a transformer and might only work on AC. The meter should say what type of current it will read. P E H
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