glow plug voltage issues

[thumper]

hi folks its been a while

2 new rads, coutless hoses, new turbo to name but a few - anyway heres the latest if anyone has any guidance it would be a help

have been replacing glow plugs at the alarming rate of 4 every 4 months approximately

have just checked the voltage across the buzz bar - 13v - then to 9 then to 3 then off - all as expected, but on start up the relay clicks in again and sends 11 volts back to plugs and continues to do so- which its not supposed to do as once pots are warm enough for combustion to take place they need not be on which we have proved by disconnecting the relay and starting after a normal start - all ok - but why would the relay deliver 11 v after ignition???? - the relay itself is ok - its what is sending 11 volts back to the relay????

any idesas would be appreciated

[jaky cakes]

If your relay is pulling in after engine running - then I would suggest your relay "trigger" side is at fault - ie preheat timer unit - which in turn is governed by the speed sensor.
Is your relay changing state ie on/off or is it being held in or have the contacts fused together.

[thumper]

we think we may have narrowed it down to water temp sensor on the block as this will make the relay stay on for cold starting? its clicking off then back on as soon as the engine starts - the relay itself it in perfect condition internally.