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1968 Ford Mustang — temperature climbs in traffic but drops once moving

LongMilesHauler140Community StarterJun 12, 20261968 Ford Mustang FastbackNew York
1968 Ford Mustang Fastback, about 180,000 miles. Coolant temperature rises while sitting with the A/C on, then drops once the car is moving. Coolant level looks correct. Fans run, but I do not know whether they are reaching full commanded speed. Mostly looking for the right next step.
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10 replies

DailyNomad621Community StarterCommunity StarterJun 12, 2026permalink
Log the conditions before you spend. Capture voltage while the 1968 Ford Mustang is actually failing — after it restarts you've lost the clue. You'll know quickly if you're on the wrong tree. On “temperature climbs in traffic but drops once,” that was the fork that mattered for me. That's the sequence I'd use. Climate here is different, so treat that as a local data point. This is the version I'd tell a friend.
TrailRoadieCommunity StarterCommunity StarterJun 12, 2026permalink
I wouldn't throw parts yet. If a shop can't duplicate it on the 1968 Ford Mustang, bring a video plus freeze-frame data, not just a story. Save the big job until that test fails. That's the whole play. Might be overthinking it, but I'd rather overthink than overspend.
ColdStartFanCommunity StarterCommunity StarterJun 12, 2026permalink
I'd want a measurement, not a hunch. Loaded-suspension checks on the 1968 Ford Mustang catch play that a wheels-hanging inspection misses. If the cheap test changes it, stop and reassess. Do that first. I refuse to clear codes until someone else sees them.
LongMilesHauler140Community StarterCommunity StarterJun 12, 2026permalink
Cleared nothing. I want service to see the alert on the 1968 Ford Mustang first. Only after sitting overnight so far.
TrailRoadieCommunity StarterCommunity StarterJun 12, 2026permalink
This is usually cheaper to test than to guess. If a shop can't duplicate it on the 1968 Ford Mustang, bring a video plus freeze-frame data, not just a story. Don't erase codes until someone who can help has seen them. This is from a 1968 Ford Mustang in New York with 180,000 miles. Do that first. I'm keeping receipts and dates in one folder.
CommuterCommuter3Community StarterCommunity StarterJun 12, 2026permalink
Ask what changed right before it started. Swap the cheap/easy piece first on the 1968 Ford Mustang and see if the fault moves. That's the branch I'd chase this week. Had a similar mess a couple years ago and that's what finally sorted it. I keep a notes app thread for this now.
ShiftCollector423Community StarterCommunity StarterJun 13, 2026permalink
Log the conditions before you spend. Write temp, speed, and in-gear vs coast when the 1968 Ford Mustang does it — then decide on parts. That's the branch I'd chase this week. On “temperature climbs in traffic but drops once,” that was the fork that mattered for me. I'd want a dollar figure or a measured spec, not 'should be fine.' That's my plan before I call anyone.
LongMilesGuy639Community StarterCommunity StarterJun 13, 2026permalink
If it were in my driveway, two 1968 Ford Mustangs can feel identical and have different causes, so measure before you copy someone else's repair. Save the big job until that test fails. This is from a 1968 Ford Mustang in New York with 180,000 miles. Do that first. Happens in gear, not in park, for what that's worth.
ShopLearner329Community StarterCommunity StarterJun 13, 2026permalink
Ask what changed right before it started. Write temp, speed, and in-gear vs coast when the 1968 Ford Mustang does it — then decide on parts. If the cheap test changes it, stop and reassess. This is from a 1968 Ford Mustang in New York with 180,000 miles. No need to make it theatrical. A day of patience here is cheaper than a wrong part. Only after sitting overnight so far.
ShopHunterCommunity StarterCommunity StarterJun 13, 2026permalink
Intermittent stuff lies if you only catch it once. Write temp, speed, and in-gear vs coast when the 1968 Ford Mustang does it — then decide on parts. That's the branch I'd chase this week. On “temperature climbs in traffic but drops once,” that was the fork that mattered for me. Run the total, not the monthly, before you commit. Climate here is different, so treat that as a local data point. Might be overthinking it, but I'd rather overthink than overspend.
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