Having problems with the thermostat in a 4.9
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1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, Having problems with the thermostat in a 4.9 in Past Cadillac Vehicle Discussion; I have a 95 deville 4.9. When I did my whole WP / timing cover job I also changed the ...
  1. #1
    TGOT is offline Cadillac Owners Member
    Automobile(s): 1995 Deville 4.9
    Join Date
    Oct 2013
    Age
    27
    Posts
    18

    Having problems with the thermostat in a 4.9

    I have a 95 deville 4.9. When I did my whole WP / timing cover job I also changed the thermostat.

    I used a 195 degree failsafe. I've gone through two of these, both times they are getting stuck all the way open as if the car overheated. I've been watching my coolant temp and the hottest the dash readout ever gets is about 220, and that's only for a moment and it goes back down. From what I've read the rad fan doesn't even kick on until 230 ish. The car never seems hot after a normal drive. Yet after a few days the thermostat gets stuck open and the car won't go over 140, forget operating temp.

    I know I'm installing it the correct direction but unless I got a pair of dud thermostats or these are not suitable for the normal temps of the car I'm confused. Two duds seems unlikely.

    So what is the normal operating range of the 4.9?
    Is this possibly too high for the thermostat I'm using?
    What have ya'll used in the past that worked?
    Anything I might be doing wrong here?

    Thanks all.

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  3. #2
    MoistCabbage's Avatar
    MoistCabbage is offline Cadillac Owners 10000+ Posts
    Automobile(s): Crimson 2001 Seville STS, 1990 Seville (RIP)
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    Fail open thermostats are useless. If the engine is overheating, the thermostat will be wide open, and it will stay that way until it cools down. All a fail open thermostat does is endure you'll have to replace the thermostat when it opens too far.

    Get a normal Stant thermostat.

    Normal temp range is ~190-220 or so under most driving conditions.

  4. #3
    TGOT is offline Cadillac Owners Member
    Automobile(s): 1995 Deville 4.9
    Join Date
    Oct 2013
    Age
    27
    Posts
    18
    Thread Starter
    Thanks will do! Here I thought I was doing a good thing.

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