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disco 300tdi heater plugs


geoff.

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Welcome :)

In the first instance put a voltmeter on the plug terminal and turn the ignition on - you should get 12v there for a while and then there should be a clear click after a few seconds when the relay cuts out, at which point the voltage should disappear. If there is no voltage, there's a problem in the electrical feed, possibly the timer/relay is kaput.

If this is OK, put a voltmeter on the battery and do the same. If the plugs are working and drawing current, you should see the voltage pop up by a bit when the relay drops out. If there is no change in voltage, they are almost certainly blown. The only sure test is to take them out and check them with jump leads and a battery. Put a jump lead crocodile clip on the -ve of the battery, and the other end of the jump lead onto the body of the glow plug. Now either connect the power terminal on the end of the glowplug to the positive with another jump lead, or just touch the power terminal onto battery +ve. You'll get a spark, so don't jump and short it out! One of three things will happen. Either nothing (glowplug f***ed), the plug will glow half way up its body (glowplug f***ed) or it will quickly glow red hot on the very tip of the plug (plug OK).

Do this for all four plugs.

Be careful how you take them out - they seize in the head (alloy head, steel plug, dissimilar metal corrosion) and will snap off which then requires the head to be removed to sort it out. Assuming they come out easily, put plenty of copper grease on the new ones before you put them in.

HTH

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Thanks BM

will test them tomorrow.

i know its a daft question but any idea where the relay is i defo can't hear it click plus the heater glow light on the dash aint working , as for the plugs they should come out quite easy i,ve just done the head gasket and P gasket and did take them out then.

thanks for your help :i-m_so_happy:

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