In my 2003 Dodge Cummins I've typically been using a blend of 66% Mobil 1300 15W40 and 33% M1 5W40, sometimes 50% - 50%, but the last time decided to try 100% M1 5W40 to use some of the stock of the older 5W40 T&S. I stocked up on it when a local retailer had it on clearance for $4 a qt.
The coolant has typically reached normal temps at the same distance from home or work when commuting, taking a bit longer on colder days. Diesels cool down when idling too much, something that I hadn't observed in the past. After changing to 100% 5W40 it consistently takes a few miles farther to get to temp, and for the first time I've observed the coolant temp dropping noticeably when idling too much in stop and go traffic. It still reaches normal temps with regular driving loads, but taking longer to warm up and cooling when idling too much are consistent symptoms of running cooler. Note that the truck has an excellent cooling system, as I've never seen it get above normal temps with any payload (I don't tow) on any grade in any ambient temps.
I'm also running a blend of fuel additives, Stanadyne 'Performance' which is a cetane booster / gel point reducer / lube, with Stanadyne lube additive. I've been running that combination since fall, before using 100% 5W40.
The combination of using foam to quiet a clanky hood latch, the fuel additive and the 100% 5W40 have resulted in a noticeably quieter engine, with no common clicks / clacks / ticks / knocks. The engine revs a bit easier on cold days when warming up, and being quieter I'll probably continue to use 100% M1 5W40.
The coolant has typically reached normal temps at the same distance from home or work when commuting, taking a bit longer on colder days. Diesels cool down when idling too much, something that I hadn't observed in the past. After changing to 100% 5W40 it consistently takes a few miles farther to get to temp, and for the first time I've observed the coolant temp dropping noticeably when idling too much in stop and go traffic. It still reaches normal temps with regular driving loads, but taking longer to warm up and cooling when idling too much are consistent symptoms of running cooler. Note that the truck has an excellent cooling system, as I've never seen it get above normal temps with any payload (I don't tow) on any grade in any ambient temps.
I'm also running a blend of fuel additives, Stanadyne 'Performance' which is a cetane booster / gel point reducer / lube, with Stanadyne lube additive. I've been running that combination since fall, before using 100% 5W40.
The combination of using foam to quiet a clanky hood latch, the fuel additive and the 100% 5W40 have resulted in a noticeably quieter engine, with no common clicks / clacks / ticks / knocks. The engine revs a bit easier on cold days when warming up, and being quieter I'll probably continue to use 100% M1 5W40.
