Our van has been progressively getting worse at starting up in the morning. It only has issues when the engine is cold.

Initially I thought it might be the glow plugs. I tested their resistance and they are all at about 1 ohm. I have also voltage tested them and found similar value to battery reading ie. about 12.5v. So I then thought to check wiring and relay by putting my meter between the glow plug and the glow plug cap. Here I get a 11v reading... Shouldn't this be 12v? Is there anything else I can try to troubleshoot the problem?

My van is a Renault Master 2003, got 80k miles and no service history so don't know what jobs have been done...

Any help is truly appreciated.


  • 1
    How cold are we talking about here? And If you're measuring voltage with a resistor (glow plug) in line, your reading could be a little lower than expected, so depends on exactly how your taking the measurement.
    – JPhi1618
    Commented Jan 18, 2016 at 16:11
  • 1
    When you tested the glow plug resistance, did you disconnect the wires to them first?
    – HandyHowie
    Commented Jan 18, 2016 at 16:18
  • We are talking just over 0C / 30F... Commented Jan 18, 2016 at 16:48
  • i did disconnect the wires first... Commented Jan 18, 2016 at 16:48
  • btw: the reading is with the glow plug in line... Commented Jan 18, 2016 at 16:49

2 Answers 2


One possibility is low cylinder compression, either due to gases getting passed the piston rings or passed poorly seating valves.

If gasses are getting passed the rings, this could possibly be detected by removing the oil filler cap while the engine is running, if you then put your hand over the filler and feel a large volume of gas being blown out of the filler, you likely have worn piston rings.

  • @Zaid Possibly, what have I missed? I don't know a simple way of detecting leaking valves on a diesel, if that is what you mean.
    – HandyHowie
    Commented Jan 19, 2016 at 21:32
  • For some reason the only word I saw from your last paragraph was "If". I guess my page hadn't loaded completely.
    – Zaid
    Commented Jan 19, 2016 at 21:33
  • When you say "large volume of gas", what do you mean? there is some air coming through but I'm not sure whether I have worn piston rings... Interestingly, this morning, it just wouldn't start, so i called the RAC and they sent a mechanic out... I explained the multimeter tests I did and he said he was pretty sure it was the glow plugs anyway. He then sprayed the air filter inlet with some easy start and the van started with no much diesel smoke (as opposed to other times recently). He suggested that easy start working is a good indication that the issue is the glow plugs. Is this true? Commented Jan 20, 2016 at 14:35
  • Also one of my injectors is leaking - there is no diesel around it but i can hear it... I am reluctant to fix it because we did this twice this year, it costed a small fortune and the problem is still there. Do you think this could cause the cold start issue? Commented Jan 20, 2016 at 14:39
  • 1
    Maybe it is just your glow plugs. Probably best to verify that they are working correctly before you try anything else.
    – HandyHowie
    Commented Jan 20, 2016 at 15:14

Quick update: After months of fighting with this issue. We took it to the mechanic. He could not replace the glowplugs but he proceeded with chiseling off the black gunk off the leaky injector and replacing the seal. The van now starts perfectly.

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