Some weeks ago I wrote:

"My 244 Diesel with D24 engine has a cold start problem.

On summertime it is OK, but when the temperature goes below 0 degrees centigrade (32 degrees Fahrenheit), the engine is difficult to start. The glow system light on dashboard operates normally. After starting, a lot of gray smoke comes for a couple of minutes and the engine runs poorly. But when the engine warms up, everything is OK.

The glow plugs (Bosch Duratherm) were changed about 1 month ago and it started well for a couple of weeks, but now it is as it was before the glow plug change.

The glow system and cold start device are OK and the engine is in comparatively good condition.

Is it possible that the glow plugs are damaged or dirty after only 1 month of operation?

So what am I supposed to do next? What should I check and/or change? Does somebody have own experiences about this? "

Some good guesses came, like Jim Bowers wrote:

"As the temperature drops ALL the glow plugs have to be operating properly. They don't get dirty, they just burn out. Is the "glow time" correct? I had a couple progamer relays fail on me and the "glow time" got to be too short. The coolant sensor that tells the program relay how long to "glow" may need attention also. My shop manual had a chart of glow time versus coolant temperature. (I sold it after I sold the car so I can't check the information for you.) Also check all the connections at the glow plugs to make sure they were done correctly. Was the place that did the work for you "qualified"? Are you sure they changed them all, or did they just check them? They are tough to get to, especially the one behind the pump, but they have to be done right because each one draws about 12 Amps of current. I found the life of the plugs was highly variable and I only changed them when one failed.

Is the cold start device on the side of the pump moving that lever through a good 15 to 20 degrees from cold to hot? Mine degraded with time and needed to be replaced eventually."

and another one from Jim Baron:

"My experience is all with VWs, Mercedes, and Minneapolis-Moline, but since your Volvo is really a VW, is suggest the following:

Remember that if your injectors are not spraying a good fine pattern, they can cause the glow plugs to deteriorate very rapidly by shooting a steam of fuel right on the tip of the plug. So start by rechecking the glow plugs to establish whether the new ones have degraded rapidly (tips burned away), which could indicate an injector rather than a glow plug problem. The guys at a VW diesel parts site (www.bright.net/~vwdiesel/) recommend the following as a means of cleaning injectors, believe it or not: get a new fuel filter and before installing it, fill it with non-synthetic ATF so that the engine starts on ATF (rather than diesel #2), which is a very powerful cleaning agent, but will burn in diesels, provided that the air and the engine are not too cold.

The ATF quickly becomes diluted with incoming #2 diesel enough that the car can be driven normally but the injectors get a good cleaning by then.

On the other hand, is it possible that your climate region is such that your fuel source does not properly reformulate its fuel for the various seasons? Try buying some other brands, especially from the big truck pumps."

Unfortunately none of these assumpitons were correct. All the glow plugs were changed and are OK. I know, because I did it myself. The fuel and the fuel filter are OK. The injectors are not that worn either and the cold start device is working. So, what next?

Please, give more hints, even if you feel that your guess would be totally irrelevant. Own experiences, etc. Thanks already.