Over a period of time the 4runner was taking more and more cranks to get started. Not slowly getting worse, but one day it was half a crank everytime, then months later overnight it was a few cranks everytime, then later it was worse. One very cold morning when it nearly didn't start I thought "I will buy a set of glowplugs today." What's a glowplug?
New glowplug on top, old glowplug underneath.
If you're driving a diesel and you don't know what a glowplug is then you need this lesson: Diesel fuel spontaneously combusts under high pressure, unlike petrol which needs a spark to fire it. So diesels don't need spark plugs, once they are running they will run forever until they are out of fuel (or you cut the fuel supply off by twisting the key...)
However, when the engine is cold it is hard for the diesel to self-ignite, this is when the glowplugs do their bit. You switch them on, they get very hot on the tip, they switch off. When you crank the engine over that hot spot is enough to get the diesel burning. Once the engine is up to temperature it doesn't matter anymore - the diesel will explode without the need for the glowplugs.
New installed glowplugs...
Down at Repco they wanted $23AUD per glowplug. I said give me 4 without even testing to see whether the old ones were okay or not. Once I pulled off the glowplug strap and hoiked them out, I did some tests...
A healthy glowplug will have a resistance across it of around 0.5 Ohms. I discoverd that 2 of mine had gone open circuit (ie the resistive heating element inside them must have failed) and one had "rattled loose" off the glowplug strap. No wonder it was hard to start with only one glowplug working...
So when a glowplug fails you won't be able to measure any resistance across it - buy a new one!
Remove the glowplug strap (that supplies power to the them during pre-start). Taking out the old and putting in the new is easy with a deep 12mm socket. Screw them in like you would a spark plug, tight but not stupidly tight. Put the strap back on. Too easy.
Now you'll be, like me, back to half a crank to start first time everytime ;)
Strap back on, ready to go.