1998 Ford ZX2 - temp gauge question

Maintenance/Repairs
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1

98 Ford Escort Zx2, 135K
Symptom:
All was well for years, suddenly at highway speed 1 day ago, temp gauge needle rose from middle to just before Red on stock temp gauge @ 55mph, outside temp 91 degrees (gauge needle normally right in middle - on hot days, rose sometimes at stop lights to about 75% of gauge, fan kicks on, goes back to middle). Terrified, but managed to get car home before overheating
Solutions attempted:

  • changed thermostat from I believe 195 degree to 180 degree
  • refilled with 50/50 mix, rinsed reservoir tank, topped off reservoir tank when ‘hot’ to hot level
  • flushed system & believe burped all air pockets (no more bubbling at radiator filler)
  • Connected OBDII and monitored temp at idle until 190 degrees
  • Fan kicks on at around 190-195
  • Upper temp sensor replaced approx. 2yrs ago, radiator replaced 2-3 yrs ago, water pump 3-4 yrs ago
  • no known water leaks, oil not foamy / milky
    Problem:
    Gauge appears operational & at temp reads at around 65% (past half way) on gauge & temp never seems go down
    Only vehicle & don’t know if I can trust car…
    What else have I missed?
2

hat 180 degree T-stat might throw an error code because the car isn’t getting up to temp. It happens.

Based on the rapid onset of the problem, I’d guess you’ve got a head gasket starting to go. Watch the water level, if it drops without a puddle… could be a head gasket. If the overflow bottle starts to show oil residue or shows bubbles when the engine is hot… could be a head gasket.

Might try renting a cooling system pressure tester at your local auto parts store to see if the cooling system holds pressure. No pressure hold… could be a head gasket!

Buy a cheap IR temp gauge as well so you aren’t relying on a 21 year old, dash mounted, no numbers, coolant temp gauge.