Mpg tanked again

[hodaka100]

I've cooked my 88 300 several times with no problems after it cooled down.
I've had my 85 300 up to at least 235 because of low coolant. I think the factory gauge was just past the L at that point. On the 88 with a undersized radiator I would often run it past the L up to the far line. I think the factory gauge works perfectly. You must keep in mind factory electric fans were often not programmed to turn on until about 238 degrees. I like to keep my engines warm, ideally 210. I get worried above 230 but that doesn't stop me from driving until I get another symptom.

 

[PSIG]

My post was for anyone, but specifically for the OP.

 

[PSIG]

I think the factory gauge works perfectly.

It does, if the sensor is responding properly and the gauge is still in calibration. But, if you haven't checked that, you can't know. I always verify gauge operation before diving into cooling system issues, because they are not guaranteed to hold accuracy. Estimates are that more than half of "cooling problems" are bad gauge readings. Trust, but verify.

You must keep in mind factory electric fans were often not programmed to turn on until about 238 degrees.

Check the Ford Shop Manual for your year, model and engine. Most Ford models since the '80s I've worked on have E-fan turn-on at ±20° above thermostat rating, usually 210°-215° for a 192° thermostat. Mechanical clutch fans are at max engagement around 185° for any thermostat.

At what temperatures do fan clutches engage?
Answer:

Most fan clutches engage at about 170°F air temperature (about 180-190°F engine temperature). They reduce the temperature about 20°F before disengaging.