checking glow plugs

   / checking glow plugs #1  

gyroman

New member
Joined
Jan 30, 2001
Messages
2
I think I might have one or more bad glow plugs on my kubota so I put a ohm meter lead on the block and
the other lead on the glow plug terminal and it read zero. Is this a good reading or is my glow plug bad.
I appreciate any and all tips for checking them correctly.
Thank You.
 
   / checking glow plugs #2  
Do you mean 0 as in "no resistance", e.g. short, or 0 as in infinite resistance, or open. I would expect a glo plug to have a little resistance, on the order of 5-10 ohms. Make sure you meter scale is low enough to detect a few ohms. Did you check all of them?

Larry...
 
   / checking glow plugs #3  
gyroman, I'll echo what LarryT said. I don't find here, or in your profile, what model Kubota you have, and I'm sure the proper reading is going to be different for some of the older models vs. the newer ones. My B2710 manual shows to check continuity between the glow plug terminal and the chassis and "If 0 ohm is indicated, the screw at the tip of the glow plug and the housing are short-circuited. If the factory specification is not indicated, the glow plug is faulty. Factory spec. Approx. 0.9 ohms"

Bird
 
   / checking glow plugs #4  
Thanks Bird. Even less resistance that I guessed. 0.9 ohms could easily be mistaken for a short. I'd guess that a glo plug failure mode could be either open or short. But I'd doubt all of them would fail at the same time. Look for differences.

Larry...
 
   / checking glow plugs #5  
gyroman,

I might be able to help if you can tell me what meter you are using. My manual (B21)says the same as Birds ~ 0.9 ohms. Most digital meters do a poor job of low resistance measurements.

Analog meters like the Simpson 260 (30,000 ohms/volt) can distinguish dead shorts from low resistances.

Either way, try this, short the meter leads togather and if it is an analog meter use the Rx1 scale and zero the meter and then measure the plug, if it is a digital meter, short the leads togather and remember the reading. Measure the plug and subtract the reading with the leads shorted.
 
   / checking glow plugs #6  
Best check in a manual. My Ford 1710 manual gives resistance specs for the individual plugs and for the wiring. Best to be clear on whether a spec like .9 ohm refers to the parallel plug connections or to each individual plug. A parallel connection of three .9 ohm loads draws about 40A. A .9 ohm load draws about 14A. Ahh Uhm--it's early and my arithmetic may be suspect.

Glow plugs themselves are either good or bad. They don't get weak, but contacts or bases can become corroded, which slows them down. A poor connection on one plug would be reflected in a resistance measurement that is higher than spec. If the spec is given for the parallel connection, the reading would still be higher than spec. However, then you would be left with finding which particular connection is poor. It's not good to have one doggy plug, because the other cylinders have to be over-heated before the doggy one gets hot enough to fire.

Another way of checking plugs is to remove them, clean everything. Then, connect them to the wiring, hold the base against the cylinder head, turn on the pre-heater and see if they glow. If it glows, the plug is good, but connections in the wiring harness still may be bad. ‘Holding the plug’ involves the usual precautions when working with electricity. You don’t want to weld a wedding band to your finger.
 
   / checking glow plugs #7  
Twinkle, I found your comment about digital meters interesting. I use a digital meter for the very purpose of low ohm resistance. It is so accurate. It is on the very high resistance loads, those in the meg ohms that digital gets a little quirky. What I observe with a high resistance is that a digital will continue reading many times per second a different resistance and refelect that on its screen. That being said, I actually find a test lamp being the easiest and sometimes the most accurate way to determine a glow plugs state. Glow plugs, like light bulbs tend to either work or not. Very rarely do they "short" but rather "open". I was also curious as to the posters reason for questioning his glow plugs. Is his machine starting hard? Here in California I have yet to use a glow plug on my Kubota, even once. I figure that since it starts in about 1/2 second everytime even after 10 years, it just doesn't need the assitance. Now my Ford diesel, its a different story... Rat.
 
   / checking glow plugs #8  
I guess I will echo what others have said here, with the added information that glow plugs, like light bulbs, change resistance when they warm up. So the 0.9 ohms will become much larger, very quickly after 12V is applied. That said, a DVM applies a relatively small voltage, so won't cause the glow plugs to warm up, or to change resistence (at least not enough to notice).

The bottom line is to use the lowest scale available to see if your glow plug is there. The difference between 0.9 ohms and 0 is not very much, and will look like the same (as in a short) if you're on a 2 Megohm scale.

GlueGuy
 
   / checking glow plugs #9  
In my experience with checking resistance of glow plugs with a dvm; check the ohms in the lowest and the next lowest ohm position. I tried it in the lowest position and it ran down to zero. the 20k position read 2 ohms which is the correct reading for the L245. Unfortunately now i have three extra glow plugs. If a dealer is nearby get hte new plugs and test a new one for your model type. As stated earlier any variation of reading from plug to plug would be cause for concern.
See my earlier "L245 hard start "post under my unregistered callsign.
 
   / checking glow plugs #10  
Further to my last. Make sure you disconect the leads from each glow plug when doing the test so no parallel readings occur. ie it has to be an individual test of each plug.
Am going up this fri to check the injectors on my L245. Any suggestions on "home checking tips". I've read the manual on having the required test equipment (which i don't have) so was just going to pull the injectors and fire each one into a clean parts washing can( to catch to fuel) and observe the spray pattern and if they start and stop the spray quickly and with no drip. Will also check the condition of them for obvious damage and cleaning required. Any other suggestions???
 

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