Just replaced cooling system on my 2000 540 (cracked radiator neck, of course), been wondering if a 70/30 mix of antifreeze would avoid an untimely repeat. So I took some measurements:

About 80F ambient, car idling, A/C off. Engine core temp ("KTMP") from on-board computer. Coolant temp from OBDII scanner.

2000 540: KTMP 108-111C. Coolant 228F (109C). Thermostat OE 105C. Since 50/50 mixture boils around 223F, there would be substantial pressure @ 228F. Would it make sense to go with a 70/30 mix that boils at 235F, to reduce operating pressure @ 228F? Any drawbacks to doing this

For grins I also measured 2002 M5: KTMP 82-85C, Coolant 176F (80C). Thermostat OE 79C. Now I'm seriously confused :-) I thought these two engines are similar, didn't expect such a large temp delta. Is BMW running 540 too hot (thus cracking radiators), or M5 too cold (due to some other weakness, such as weak heads)?

Thanks!

• 70/30 antifreeze mix better than 50/50? - thisolde39 2008-05-12 17:01:44 (108 views)
  • Re: 70/30 antifreeze mix better than 50/50? - jimcash 2008-05-14 11:15:42 (123 views)
    • Re: 70/30 antifreeze mix better than 50/50? (pic) - thisolde39 2008-05-14 21:49:00 (150 views)
      • Re: 70/30 antifreeze mix better than 50/50? - jimcash 2008-05-18 12:50:07 (63 views)
      • Your pic is quite common for the V-8 4.4L engine. (nt) - hypercritic 2008-05-15 04:50:17 (96 views)