I only replaced 1 bad one I had with a Bosch from Autozone. No problems yet. Haven't seen any upgrades for the OM 602.962 as far as plugs. The factory system is pretty good.
Looks like Afterglow was incorp in 1989.
There is a temp sensor that will determine afterglow time.
It basically works like this.
Glow system turned on 30 amps to each glow plug, Heats glow plug very rapidly Amps drop to approx 8-15 amps. After 9 secs glow plug reaches 900 deg C temp, 1180 deg C max after 30 sec.
When glow system is switched on. Preglow indicator lamp in instrument cluster lights up. Glow durations is determined by temp sensor. Preglow indicator goes out indicating that the engine is ready for starting.
AFTERGLOW TIME:
When temperatures are below approx 0 Deg C Max after glow time is 60 seconds.
These are approx time periods.
30 Deg C No Afterglow
25 Deg C 10 Sec Afterglow
20 Deg C 20 Sec Afterglow
15 Deg C 30 Sec Afterglow
10 Deg C 40 Sec Afterglow
5 Deg C 50 Sec Afterglow
Overall seems like a reliable well designed system on the W124 OM 602.962.
FAULTS:
Before 1988: Preglow indicator fails to light up when key moved to #2 position.
As of 1989: Pre glow indicator lamp fails to light up when key moved to #2 position. in addition: the preglow indicator lights up for approx 1 minute when engine is running.
Possible faults:
Interrupt in cable connection to terminal 30
Preglow time relay faulty
interrupt in one or several cables to the glow plugs or glow plugs
short circuit in system.
Pre 1989 systems have 80 ampre fuse built in. could be bad.
Check out this link:
http://www.peachparts.com/shopforum/archive/index.php/t-246719.html