Been following several threads about transmission temperature and fluid changes. Decided to start a new thread about my own experience.
Based on my sense of the many threads on the subject, I decided to get a transmission fluid and filter change at 75,000 miles. After a few days of driving around town, I got back on the highway. Uh oh. Before the change, the transmission would warm up fairly quickly, and stay in the 200F-205F range during freeway cruising (65-75, cruise control). On long grades it might have hit 210F, and on steep ~10,000' mountain passes I've reached 220F (carefully...). After the change, whoa. Got on a flat freeway, set cruise at 65, and watched temperature climb steadily over the course of about 35 miles/35 minutes, hitting 230F, at which point I pulled off to let things cool at idle before heading straight home. Didn't want to see how high it could go...
Here's the data--coolant and transmission T vs. time. Top panel: normal freeway drive before fluid change, with transmission and coolant temperatures tracking normally. Bottom panel: today's drive, on more-or-less the same stretch of freeway. Hot, hotter, hottest!
Temperatures over 220F with an empty van, no significant hills, no stop-and-go traffic, cruising at 65 in 45-degree weather. Am I overreacting? Or, should I be on my way back to the mechanic ASAP? (Note: this is the first automatic transmission I have owned in 35 years)
Based on my sense of the many threads on the subject, I decided to get a transmission fluid and filter change at 75,000 miles. After a few days of driving around town, I got back on the highway. Uh oh. Before the change, the transmission would warm up fairly quickly, and stay in the 200F-205F range during freeway cruising (65-75, cruise control). On long grades it might have hit 210F, and on steep ~10,000' mountain passes I've reached 220F (carefully...). After the change, whoa. Got on a flat freeway, set cruise at 65, and watched temperature climb steadily over the course of about 35 miles/35 minutes, hitting 230F, at which point I pulled off to let things cool at idle before heading straight home. Didn't want to see how high it could go...
Here's the data--coolant and transmission T vs. time. Top panel: normal freeway drive before fluid change, with transmission and coolant temperatures tracking normally. Bottom panel: today's drive, on more-or-less the same stretch of freeway. Hot, hotter, hottest!
Temperatures over 220F with an empty van, no significant hills, no stop-and-go traffic, cruising at 65 in 45-degree weather. Am I overreacting? Or, should I be on my way back to the mechanic ASAP? (Note: this is the first automatic transmission I have owned in 35 years)