'94 EX 2.2L VTEC- Air temps have been in the upper 90's all week... While driving on thex-way 5th gear, with cruise engaged at 70-80mph, running 3000rpm, and withA/C running, temp gauge reads just below red line... Turn A/C offlower vehicle speed to 60-70mph and engine speed at 2000-2500 temp gauge plumets to under mid-way only after half a mile. Iknow A/C is a big strain on theengine but whay would the temp drop so rapidly? Is my t-stat maybe not operating properly? I have not checked my coolant's boiling point but itis good color. Thanks in advance for any info guys...

-Greg


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[/align]Bought the car with 109K on it, not sure of the timing belt history

 

Maybe the T-stat isn't able to open all the way when needed? AC plus extra speed makes that much more heat to be rejected. First thing I'd try is new thermostat. But take a look inside radiator for scale build-up. You may want to get that cleaned (Super-Flush or something like that).

 

Driving this morning same conditions, except temp was in low 80's, and the temp gauge never went past halfway

 

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your radiator could also be clogged, highway speed should not affect the engine temp. that much even with the A/C on. More times than not when driving like that and the temp rests just below hot the radiator is the most likely culprit.