K-jet WUR 350 vs 450SL

Hi Volker, although EPC has the same part number for both the 350 and 450, the actual Bosch part numbers are different

350SL p/n is 0438140028
450SL p/n is 0438140056

Are you aware of any documentation which explains the differences between the two, or are data sheets available?

Hi Jim,

Easy answer: Both Warm Up Regulators (WUR) were used on 350 SL and I will next verify 450 SL Europe.

Long answer:

• Bosch used 0 438 140 028 WUR till 2/77 and then switched to 0 438 140 056.
• To make it even more complicated 0 438 140 056 was further modified without change of Bosch no in 1979
• All 3 types differ in warm full-load control pressure slightly from 2.7 to 3.0 (don't ask me how many stomes per squarefeet )
• They also have slight variations in cold control pressure of 0,1 bar
• Idle-run warm control pressure is the same in all 3 versions

Okay, now you are down on your knees, begging your fromer accelerator colleague to show mercy in this

I would choose a 1980 WUR 0 438 140 056 and believe that Bosch and Mercedes-Benz were wisest in the latest version. MB obviously has triggered these changes but did not bother to make a big fuzz about it.

And now to 450 SL Europe

• It started with WUR 0 438 140 010 and then continued with 0 438 140 056 in 9/77
• 010 behaves ike 028 in cold start but it behaves like early 056 in full-load warm.

Again a late 056 seems to be a good choice. What else do we learn from that? Well Bosch experimented a lot together with Daimler on the right settings for the engine until they finally created the universal 1980 WUR 0 438 140 056 . Maybe it did not matter any more during that last year where they had already launched 450 SLC 5.0 .

And please this all is only vaild for 450 SL Europe. 450 SL US / CAN / JP / AUS is a totally different animal.

Hi Volker, all very interesting to see and understand the history. I had originally planned to cosmetically restore the older unit but will no longer do that, instead I will stay with the 056 (1980) unit. Although my car is a 1979, car the engine is from a 1980 SLC.

As it seems to be working well I will not rebuild, just clean, de-rust and polish.