glow plug voltage

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matt1295

New Member
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Scarborough
been testing my glow plug voltage today and come across this

12v into relay
10.8v at the glow plugs


so found the relay and took it off cleaned all pins and check the relay socket all ok rust free

refit and test still the same
next i try 12v down the wire to the glow plugs and still only 10.8v at the glow plugs

what could be causing this
 
If you are checking the voltage when applying the voltage (ie activating them by using the ignition key), there will be a considerable voltage drop due to the extremely low resistance/high current draw of the glowplugs themselves.

I assume you're measuring the "voltage at the relay" at the input pin. Try measuring it on the output pin (ie the start of he wire that goes to the plugs) and you will get the same lower voltage.
 
yes at the relay i have 12v going in to the relay and the output connection only reads 10.8v

but if i by pass it it still only reads 10.8v at the glow plug which i thought would read 12+
 
No,for reasons I have quoted about, there will always be a significant voltage drop (at the plugs) from measured battery voltage.
 
Glowplugs pull a lot of amps so there is a volt drop in the wiring. The glowplugs are normally rated at 11 volts for that very reason, so 10.8 volts is near enough.
 
matt1295 said:
yes at the relay i have 12v going in to the relay and the output connection only reads 10.8v

but if i by pass it it still only reads 10.8v at the glow plug which i thought would read 12+
Click to expand...

How did you bypass the relay?
My Rover 400 supplied 12 volts to the plugs 10.8 sounds a little bit low to me. The glow plug circuit should handle the 50 amps the plugs pull without excessive drop
 
Last edited:
what i ment was i took the relay out and had the volt meter on the plugs and sent the live down the wire from the relay connection just to see what Voltage i was getting that way

if that makes sense to you
 
I have a cold start problem with smoking only in very cold/freezing temps can fill the street with smoke while cranking and then a big puff once running while having lumpy tick over after the throttle used its normally clears
 
After the relay it goe's to the quick start box of magic tricks that are full of dark secrets like measuring ambient tempriture to calculate how long to stay on an an an clever fings :)
 
If folks reckon 10.8volts is ok at the plugs then surely the next step is to see that the plugs are actually glowing at that voltage.
 
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