Testing glow plugs with charger - Page 2 - PeachParts Mercedes-Benz Forum

1975300D · #16 08-07-2011, 09:59 PM

Sorry guys, I tested them again after cleaning off the carbon deposits. Now they all test 0 ohms.

The broken one was the one where the retaining nut was rusted on and broke the threaded shaft.

compu_85 · #17 08-07-2011, 10:04 PM

Well, now you can upgrade to the newer style plugs and enjoy faster, better starts

barry123400 · #18 08-07-2011, 10:04 PM

I think these loop plugs are only 1.3 volts with the major part of the voltage drop across the resistance wiggle wires. A battery charger will put out too much voltage if it is capable of delivering the amperage. You were perhaps lucky you did not burn them out.

Ohmeter test is about all the average guy will be able to do plus physical observation of the loop on the end of the plug. Newer type plugs are twelve volts and draw perhaps 20 ampres when cold initially so a car battery for them is best again for the average guy unless you have a really powerful battery charger.

1975300D · #19 08-07-2011, 10:04 PM

But what about the relay problem? Will the dealership know what to give me?

barry123400 · #20 08-07-2011, 10:24 PM

I am not quite sure what you mean. Will the dealer know. If you are not updating the system then a relay from the auto wreckers would do quite well if needed. They are fairly expensive from the dealer. Anyways get your old system running to see if anything is needed.

JHZR2 · #21 08-07-2011, 10:29 PM

Battery charger will both current limit and also try to determine if it is short circuited to self protect. Likely one of these things was indicated due to the glow plug looking different electrically than a battery...

1975300D · #22 08-08-2011, 12:42 AM

Barry, you suggested I use the pencil type, but I'm told they need a different relay, so I'm hoping the dealer gives me plugs that work with my original relay.

There are no mercedes benzes in the wreckers around here! And certainly no classic W115s.

sjh · #23 08-08-2011, 12:48 AM

Quote:

Originally Posted by 1975300D

Barry, you suggested I use the pencil type, but I'm told they need a different relay, so I'm hoping the dealer gives me plugs that work with my original relay.

There are no mercedes benzes in the wreckers around here! And certainly no classic W115s.

Why can't he just take the output lead from his existing relay, hook up a 5 way split and run the leads to the plugs.

My '75 240D had the hand pull on the dash and the cherry glow indicator.

Does this man really need to buy a new relay?

kerry · #24 08-08-2011, 08:46 AM

There have been threads on here in the past regarding the 115 300d relay and pencil plugs. I'm virtually certain that all those threads concluded it won't work. Although in my opinion, it is definitely better to install the pencil plugs and a ford starter relay.

When you tested the ohms on the plugs, where did you run the current? Was it from the outer ring connection to the stud? You can't check the resistance of a loop plug by going from the body of the plug to the threaded stud like it's done with pencil plugs.

I think you could test those plugs by attaching the heavy wires to them and then putting the voltage from the charger thru 4 of them at once.

Palangi · #25 08-08-2011, 08:42 PM

Quote:

Originally Posted by 1975300D

Sorry guys, I tested them again after cleaning off the carbon deposits. Now they all test 0 ohms.

Something is amiss with the method of measurement. Zero ohms would be pretty much impossible. If measured correctly, it should show in the neighborhood of 5 to 10 ohms.

As stated previously, any plug with a completely intact loop is virtually certain to be good.

Hang in there. You will get this figured out.

79Mercy · #26 08-08-2011, 08:46 PM

Quote:

Originally Posted by Palangi

As stated previously, any plug with a completely intact loop is virtually certain to be good.

.

not true, could be broken inside.

These are 6 volt plugs btw

Palangi · #27 08-08-2011, 09:03 PM

Quote:

Originally Posted by 79Mercy

These are 6 volt plugs btw

Take a look at the wiring diagram in post 23 of the other thread.

Those plugs glow on about 1 volt each. As I recall. they are actually rated at about 1.6 or 1.7 volts or so.

1975300D · #28 08-08-2011, 09:15 PM

I test the ohms by putting one lead to the body and one to the tip. On the old ones, the readings are from 5 to 50. On the new ones, the readings are 0.

79Mercy · #29 08-08-2011, 09:16 PM

Quote:

Originally Posted by 1975300D

I test the ohms by putting one lead to the body and one to the tip. On the old ones, the readings are from 5 to 50. On the new ones, the readings are 0.

this is not correct. put one lead to the threaded post, and the other to the ring around the threaded post