seems to be loosing prime....but.....? - Page 2 - PeachParts Mercedes-Benz Forum

Diesel911 · #16 11-25-2012, 08:59 PM

If you have the cheap Harbor Freight type Meters you need to put your 2 probes together touching each other and see what resistance reading you get.

What ever that reading is you need to subtract from what you get on your Glow Plugs

whunter · #17 11-26-2012, 10:27 AM

Quote:

Originally Posted by TnBob

Just to be clear, the ohm reference point is:
"A new glow plug reads 0.7 OHM"

That is correct.

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whunter · #18 11-26-2012, 11:59 AM

Quote:

Originally Posted by vstech

I would venture to say .5 to .8 is good. 1.0 will work, but verifying visually is wise.

I disagree.
The good range is 0.7 - 0.9 OHM.
My experience with low readings is all bad.

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vstech · #19 11-26-2012, 12:48 PM

wouldn't temp be a factor? .5 for a REALLY COLD plug...

TnBob · #20 11-26-2012, 09:23 PM

Test one in your freezer at home John... I think you will find that .7ohms is .7ohms

whunter · #21 11-26-2012, 09:52 PM

Quote:

Originally Posted by vstech

wouldn't temp be a factor? .5 for a REALLY COLD plug...

Refer to operating temperature.

The resistance on good quality glow plug's is amazingly consistent -40° F through +140° F.

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funola · #22 11-26-2012, 10:54 PM

Quote:

Originally Posted by whunter

I disagree.
The good range is 0.7 - 0.9 OHM.
My experience with low readings is all bad.

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Unless your measurements were made with a piece of equipment called a milli ohm meter, they are probably inaccurate.

Brian Carlton · #23 11-26-2012, 11:12 PM

Quote:

Originally Posted by funola

Unless your measurements were made with a piece of equipment called a milli ohm meter, they are probably inaccurate.

How true.

They make the measurement with an instrument that is graduated in tenths of an ohm and draw a conclusion based upon a difference of one tenth of an ohm...............the error in the meter is equivalent to almost .1 ohm (unless it's a $1000. meter).

whunter · #24 11-27-2012, 09:00 PM

Quote:

Originally Posted by funola

Unless your measurements were made with a piece of equipment called a milli ohm meter, they are probably inaccurate.

I don't see how this is possible.
To me the reading is only a reference.
The only test I consider valid is removal and glowing in a vice.
Accuracy 100%.

Note to new members.
We go through this discussion on the forum frequently.
If you want reliable cold starting in sub zero temperature follow my test method and replace bad glow plugs.

New glow plugs are cheaper than a car that will not start when needed.

Have a great day.
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qwerty · #25 11-27-2012, 11:53 PM

Quote:

Originally Posted by whunter

The only test I consider valid is removal and glowing in a vice.
Accuracy 100%.

Just recently, my '83 300D went from starting great to starting not so well. A quick check of GP resistance revealed 4 plugs in the 0.6-0.7 Ohm range and one at 28 Ohms. So I replace the odd plug with a new one and the engine goes back to starting great.

What reason would I have to test any of my glow plugs in a vice? And add another hour to the job.

vstech · #26 11-28-2012, 07:15 AM

Quote:

Originally Posted by qwerty

Just recently, my '83 300D went from starting great to starting not so well. A quick check of GP resistance revealed 4 plugs in the 0.6-0.7 Ohm range and one at 28 Ohms. So I replace the odd plug with a new one and the engine goes back to starting great.

What reason would I have to test any of my glow plugs in a vice? And add another hour to the job.

the reason would be if the one plug you found out of spec did not solve the issue.

Brian Carlton · #27 11-28-2012, 09:32 AM

Quote:

Originally Posted by qwerty

What reason would I have to test any of my glow plugs in a vice? And add another hour to the job.

If you want "reliable starting in sub-zero temperatures", the test with an ohmmeter isn't considered to be sufficient to ensure that that the plug has an accurate tip temperature.

For 99% of the forum members, the requirement to pull all plugs and test them in a vice for absolute assurance of 100% performance isn't required.

I've never tested a glow plug in a vice. The test with the ohmmeter has worked with 100% precision for the past 10 years.

funola · #28 11-28-2012, 08:18 PM

Quote:

Originally Posted by whunter

Originally Posted by funola
Unless your measurements were made with a piece of equipment called a milli ohm meter, they are probably inaccurate.

I don't see how this is possible.
To me the reading is only a reference.
The only test I consider valid is removal and glowing in a vice.
Accuracy 100%.

.

A DVM is not designed to measure low resistance (i.e. anything less than 1 ohm) accurately. To do that, you need a milliohm meter that is pretty expensive and out of reach for most

Milliohmmeter - TestEquity

Milliohm meters use a 4 lead test probe in a bride configuration in order to get accurate low resistance measurements.

It's funny how people here argue whether the glow plug should be 0.5 or 0.6 or 0.7 or o.9 ohms when their DVM is not capable of measuring down to that accuracy.

A DVM is good to tell you whether a glow plug is open circuit i.e burned out or not, that's about it. If you find a glow plug with no reading (open circuit), replace that glow plug. Trying to measure the glow plug resistance with a DVM to see if it is within spec is not possible.

Pulling out all the glow plugs to test in a vise is a bit extreme IMO. Much easier to apply power to each glow plug while still in the engine with an ammeter in series so you can measure the actual current being consumed by that glow plug. It should start at around 18 to 20 amps and slowly drop to 10 amps as it heats up to it's final temp. If it does that, it is good. If not, it is NG.

whunter · #29 11-29-2012, 10:15 PM

Quote:

Originally Posted by funola

A DVM is not designed to measure low resistance (i.e. anything less than 1 ohm) accurately. To do that, you need a milliohm meter that is pretty expensive and out of reach for most

Milliohmmeter - TestEquity

Milliohm meters use a 4 lead test probe in a bride configuration in order to get accurate low resistance measurements.

It's funny how people here argue whether the glow plug should be 0.5 or 0.6 or 0.7 or o.9 ohms when their DVM is not capable of measuring down to that accuracy.

A DVM is good to tell you whether a glow plug is open circuit i.e burned out or not, that's about it. If you find a glow plug with no reading (open circuit), replace that glow plug. Trying to measure the glow plug resistance with a DVM to see if it is within spec is not possible.

Pulling out all the glow plugs to test in a vise is a bit extreme IMO. Much easier to apply power to each glow plug while still in the engine with an ammeter in series so you can measure the actual current being consumed by that glow plug. It should start at around 18 to 20 amps and slowly drop to 10 amps as it heats up to it's final temp. If it does that, it is good. If not, it is NG.

I own a milliohm meter.
I will not discuss/argue the useless readings "used Glow plugs" give.

An ammeter in series is useless, because it shows consumption, not location = tip failing to heat..

For me it is a waste of time.
45 minutes once per year to remove, examen, glow test, reinstall = "priceless" to never fail cold starting.

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whunter · #30 11-29-2012, 10:26 PM

Quote:

Originally Posted by Brian Carlton

If you want "reliable starting in sub-zero temperatures", the test with an ohmmeter isn't considered to be sufficient to ensure that that the plug has an accurate tip temperature.

For 99% of the forum members, the requirement to pull all plugs and test them in a vice for absolute assurance of 100% performance isn't required.

I've never tested a glow plug in a vice. The test with the ohmmeter has worked with 100% precision for the past 10 years.

Disagree: 40% of members don't need to use this level of testing.

IMO glow testing is needed
* If you see SNOW.
* Can't risk missing work/appointments.
* Do not like walking in the COLD.
* Have any cold start issue.

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