Glow Plugs

[m4tty]

Hi,

Can anyone have a go at this question please.

Taken glow plugs out of diesel engine and need to test to see whether they are working or not. So I made up a lead and put 12v direct across plugs and one heated up and 3 didnt so got problem sorted, however, i wanted to know whether a resistance test would have given me the answer without having to put 12v direct to it. I would have thought there would have to be a preset resistance for each plug, however when doing a resistance test live to earth the broken ones were showing a dead short 0.00 to 0.01 on the 20K range of my dads multimeter. Am i right in saying if they were ok then they would all read the same resistance and not show a dead short??

Thanks in advance, im not very good at explaining things so any replies appreciated.

Thanks

Matt

 

[kme]

You may well need a lower resitance range.

If the glow plugs were dead short, they`d fuse the pre-heat circuit......?

A resistance test will find it, think they`re only about 1 or 2 ohms (from memory)

 

[Lurch]

Depends on the car. Just looked on Autodata and mine are .5ohms. You'll need a decent meter to check on a low setting. If you give me your car details I'll have a look for you and see what the resistance should be.

 

[m4tty]

Cheers for replies it was an Escort Van Y Reg 1.8 Endura de. Can anyone access autodata as i asked someone a question on a Ford forum and they were using Autodata. If anyone can, ill have a go too. Thanks

 

[PC Electrics]

What reading did your meter give for the good one?

The test you carried out is valid. Glow plugs are supposed to heat up and I would expect them to pull 20 - 30 amps each (so about 0.5 ohm is correct resistance). However, by not heating up when voltage applied you have proven them defective.

A diesel engine will often start well (even in cold weather) with one or two GPs defective. It depends on many factors including how many GPs the engine has in the first place - not all engines have a GP in each cylinder, often just 2 or 3 cylinders.

 

[Lurch]

Legally, Autodata is a paid for service, costs

 

[m4tty]

Thanks for the replies.

Say 12v/0.6ohms = 20A.

The 20A referred to above from a 12v battery. This isnt as dangerous as 20A from a 230v supply is it. Stupid question really just trying to get head round this.

Sorry if this is well basic but i must have missed something.

Cheers

 

[sellers]

no thats right, remember you need a certain amount of voltage before you can acutually feel the electricity around 50v. So you won't be getting shocks from 12v no matter how high the ampage.

 

[newpark7]

Hi

Generally Glow Plugs draw about 15 amps each the easiest test is with a clamp meter without removing the plugs, with ignition on should get a reading of about 60 amps DC (assuming 4 glow - plugs)

Obviously you will have to take them out to find out which are working and which are not but best to replace as a set anyway.

Mark

 

[Lurch]

The 20A referred to above from a 12v battery. This isnt as dangerous as 20A from a 230v supply is it.

In what way? 12V 20A can still do some damage.

 

[sellers]

it can still cause a fire.

 

[Evans Electric]

Checking the glow plugs on my Escort Van , connect plug from batt + to earth , plug either gets hot or it doesn't. Found two duff.

Deke

 

[m4tty]

In what way? 12V 20A can still do some damage.

Where would the line be drawn as to whether you would get a shock that would hurt. 12V @ what amperage? as i always thought 12v is safe and have never worried playing about with car electrics before. Cheers

 

[m4tty]

Checking the glow plugs on my Escort Van , connect plug from batt + to earth , plug either gets hot or it doesn't. Found two duff. Deke

Done one today 3 out of 4 were duff. They get blazin hot well quick when they work dont they

 

[sellers]

I think lurch means it can still cause fire. You can't feel 12v at any ampage as far as I know.

 

[Andy™]

Where would the line be drawn as to whether you would get a shock that would hurt. 12V @ what amperage? as i always thought 12v is safe and have never worried playing about with car electrics before. Cheers

even at 12v, you can have thousands of amps flowing... but due to your body resistance and ohms law, 12v has very little flow through you, compared to 230v

 

[Lurch]

You can still cause death, fire or injury with 12V. I would exercise even more caution when working on car electrics. I have seen nasty burns from alarm batteries, and a car battery can cause a fairly impressive explosion if shorted.