I agree that generally you should replace glow plugs individually as they go bad, particularly when you have easy access to any of them that might go bad - like on a W123.

When I got this car last December it had a rather rough startup running characteristic, and the glow plug indicator in the dash did not operate. This turned out to be GP #1 which is probably the easiest one to replace. It was an interesting failure in that the GP was not electrically an open (or short) circuit, but it only drew about 3 amps rather than the 8-10 amps one should normally draw. When I got it out it was not heating on the tip, but only in the lower half next to the threaded end.

The startup characteristic improved on replacing that one glow plug considerably, but I can still tell there are one or two cylinders that don't run well immediately on startup. Everything is fine within one minute, so I think I have more weak glow plugs.

Considering the pain in removing stuff to change one or two, I'm going to undertake changing out the remaining five while cleaning the intakes. Then I should be done with the glow plug issue for several years on the car.

My worry on the crossover pipe removal has to do with thinking there might be dissimilar metal corrosion - and that I might shear off one or more bolts. Steel bolts in aluminum = trouble. It's worse around coolant, like on a thermostat housing.

Ken300D