possible thermostat problem

[thebetterman]

I was waiting for a train to pass the other day and when I looked down the temperature gage was ll the way up to the 'n'. But then I heard the fan cut in and the temperature went down to just above normal. This is the first time I noticed this happen and it never gets this high when I'm driving only when its idiling. Do I need a new thermostat or what.

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1992 Silver MTX
Completely Stock

 

[olympic]

That's normal. When your driving, air is flowing through the rad and the fan rarely cuts in. But when your idling, it's up to the fan to cool the engine. The thermostat opens at a lower temp(~190F) than the fan cuts in(~210F) so your temp gauge will go up pretty high before the fan turns on.

 

[sdpatt]

Your fan is operating so that indicates that the fan is okay. If the temperature at which the fan came on is higher than you have seen before, the temperature switch may be failing. This is an inexpensive (few bucks)switch located a couple inches below and forward of the thermostat. It could be your thermostat sticking closed, but the fan would still come on at the same temperature on the gauge that it always did, it just wouldn't have as much effect. The SHO's thermostat usually fails by not completely sealing when closed. This is due to the deterioration of the rubber seal in the Motorcraft thermostat.


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Scott

1991, 252K miles, glass hood, police grill, SVO shifter, Catz fogs,
K&N, 73mm MAF, Superchip, PP Y-pipe, Borla cat-back, 190 lph pump
Eibach/Tokico/polyurethane, SHO Shop front & rear strut braces,
16x7.5" Moda R1, 225/55ZR16 Bridgestone RE730, -1 deg camber x 4,
Class II hitch, Silver award at the SHOklahoma Car Show