TBN affected by hot or cold weather?

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May 30, 2003
South Dakota
Hypethetical scenario... 2 seperate oil changes performed on the same vehicle with identical driving style. 1st oil change done in March at 4500 mile interval after driving all winter long (northern climate) using 5w/30 Mobil 1 oil. 2nd oil change done in September of the same year at 4500 mile interval after driving all summer long on the same lot of 5w/30 Mobil 1 oil. Question: If an OA was done on oil change #1 and the TBN read 4.5, shouldn't the TBN read approx 4.5 on oil change #2 OA? How does heat or cold affect TBN if nothing else has changed with the vehicle other than total mileage on the vehicle? Ken
[Welcome!] I think that is a tough one. It really may depend on how you drive. If the car is in normal shape otherwise and you did very short trips then the TBN and the condition of the oil would be worse in the winter driving because of the excess moisture causing more wear and more oxidation and depletion of additives. If you just did normal driving and the vehicle was warned up but no real hard driving then I'd say there would be little difference. In the case of hard driving I would think that the extra stress on the oil would lead to more wear and this in turn would deteriorate oil faster. TBN would be lower. Now you have to remember though, that in both cases-depending on the amount of miles and the characteristics of the engine. The oil could be acceptable in both cases. [Cheers!]
In all likelyhood, the oil used in the winter in a northern climate will report a lower TBN than the oil used in moderate to hot weather. Generally, the oil used during the winter will accumulate more water over time as it takes longer for the oil to get to temp to "burn" or evaporate the water out of the crankcase oil. The water mixes with various byproducts of combustion forming acids that the base reserves in the oil work to counteract. Of course, much depends on driving conditions. All factors held identical except for time of year, the winter interval will likely show the lower TBN number in a northern climate like SD. I know thats how my oil behaves here in MN anyways!
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