bugnout wrote:
Just out of curiosity, Why would you see a noticeable decrease in fuel mileage. I thought the glow plugs were only active during the starting sequence. not needed after the tractor is warmed up?
Depending on conditions, the ECM will cycle the glow plugs after the engine is running as it determines is needed to maintain proper cylinder/combustion temps. That's why many people that had an EGR go south on them ended up having to have the glow plugs replaced as well (myself included) - the ECM basically burned out the glow plugs keeping them on full time in an attempt to maintain proper conditions to compensate for a malfunctioning EGR.
If the glow plugs weren't on for some amount of time after starting, until the engine is up to proper temps, and especially in cold winter weather, there would be times that engine would be kicking and bucking like a Missouri mule until it got warmed up.
Even on my old '87 MB, there's a factory mod you can do to add afterglow capability to the glow plug circuit - such that the glow plugs will be on for a certain amount of time based on engine coolant temp after starting, to aid in cold weather starting.
I found out the hard way a couple months ago the previous owner of my MB had done the infamous "purple wire" mod - he'd cut the wire from the ignition switch that shut off the GP relay after starting, such that the preglow (pre-starting) timing circuit kicked in again and kept the glow plugs on for upwards of a minute after starting. I had thought until then he'd simply done the afterglow mod. While down in Texas back in July, one day the timing circuit didn't shut off, and I drove for 30 miles before discovering the glow plugs were stuck on. I had to disconnect the GP harness itself to shut them off, and next day disassembling the relay to check it out discovered where the PO had cut the purple control wire.
I reconnected the wire, such that the GP's now shut off once the engine is running. But a couple weeks later, two of the GP's went south - burned out by the abuse they'd seen because of that shade-tree mod. I had to replace all the GP's over Labor Day weekend, and just like our CRD's, you had to remove the intake manifold to get access to all of them. I expended quite a bit of profanity that day concerning the previous owner.