82 240d

Tested my Glow Plug ohms tonight... 1.2 - 1.3 - 1.3 - 1.3 ohms

got a little confused when it said they should be under .05 ohms... or under 1. ohm

since they are not infinite on ohm measure.. are they on their way out.?? I am haveing hard start problems when temops get under 30*

thanks

An accepted target is 1.0 ohms.
0.05 ohms is too close to a short circuit, and too much current would flow.
Infinite is an open circuit, and no current would flow.

Good Thing - readings are essentially the identical and shows consistency
Good Thing - readings are around 1.0 ohms

Final test would be to remove them, apply 12V and see if they produce a bright or dull glow.

Were they completely cold when tested? The resistance goes up with temperature.

They are about 0.6 ohms on new cold plugs. Digital/analog meter as well as the quality of the meter may affect your results.

Len

I don't see anything wrong with 1.3 ohms. However, this does not exclude the possibility of a brand new plug doing a better job if it comes in at 1 ohm or less.

I have the suspicion that older plugs gain resistance over time and the tip temperature declines. If you are looking for every possible advantage, then a brand new set of plugs might be of assistance in starting.

If you do put new ones in, please repost to this thread and advise on how they did. Also, if you do it, could you take a set of readings on the resistance of the new plugs. It would be a valuable back to back set of data and the current flow between the old and new could be directly compared.

Proper valve adjustment and injection timing will also help with a cold start.

A brand new battery, or very close to new, will provide the maximum current possible and the highest cranking speed. It's mandatory on marginal engines.

I pulled the first glo plug and it looked pretty good. German mfg... how long does one apply the 12v to produce a good visual glo test?


BTW...
Tonight I added a block heater to the 4 cyl...man that was a chore!!..btw, easiest way is to remove the intake and pull the exhaust manifold toward the passenger fender and heat the plug... after cooling.... that screw in block plug came out with very little effort. Thanks Richard!

thanks again

The plug will heat up to full temperature within 5 seconds..........maybe less.

If it is taking longer than this time, the resistance is higher than desired.

Bennett,

How did U measure the GP resistance? Did you pull the cable out of the GP relay? This eliminates parallel resistance readings.

Short the leads of your ohmeter together and note the resistance reading. Then subtract this reading from the GP reading. This will give you a more accurate reading of the GP resistance. Also connect both leads of ohmeter to ground and wiggle the test clips to get the minimum resistance reading. Then measure the GP resistance.

P E H

The first thing you should try is connecting the leads of your multimeter together and checking the resistance reading. This will be non-zero and indicates part of the error in low resistance measurements.

Measuring less than 1 Ohm accurately is not easy and the proper method is to use a set of four wire Kelvin probes (high end dmm required). The Kelvin probes effectively negate the added resistance from the leads. This isn't totally necessary in your case... I'd say less than a couple of Ohms is no need to worry (if all plugs are consistent). If you had one plug that was well off the others there may be need for concern.

Your readings look fine to me.

__________________
1985 MBZ 300DT
1969 MBZ 220d
1984 MBZ 300TDT
1981 VW Vanagon

Thanks for that udate.. the glow plugs were disconnected from the loom when tested and the ohm meter read "1" when the leads were toouched together.

I would assume my readings were closer to .2 & .3 ?

That sounds much better, mine read right around 0.3 (with my very cheap meter set on the 0 to 10 ohm scale )