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Old 05-02-2012, 11:56 AM
DC DC is offline
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Any Problem with Switching to a 180? Thermostat in a Dodge 5.9L V8?

I've got a swapped-in Dodge Magnum 5.9L V8 engine in my 2000 Jeep TJ and I am about to do the plenum plate upgrade to my factory intake manifold.

While I am doing this work, I plan to replace the thermostat. I could of course just go with the same 195? thermostat that the factory used for this engine, but I have previously heard that a lot of guys have gone with a 180? unit.

I would also like to go with a 180? thermostat, however, I want to make sure that I am not going to get into any unintended consequences from a performance perspective by doing this. For example, if the PCM is looking for the engine to come up to operating temperature, I don't want to get into any potential fuel mixture or advance curve issues with the PCM wrongly interpreting the lower engine operating temp as an indication that the engine hasn't fully warmed up yet.

So, if anyone with either a Dodge Magnum 5.2L or 5.9L has switched to a 180? thermostat, or is otherwise knowledgeable about the way the PCM looks at the engine operating temp (as a function of coolant temp), please let me know if you have had any adverse performance problems or whether this move wouldn't be recommended for some reason.

Thanks in advance,
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Old 12-25-2012, 02:03 PM
Jerry Bransford Jerry Bransford is offline
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Location: Escondido, California
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I can't imagine its computer being happy all of the time with a 180 degree thermostat. Not to mention running a cooler thermostat won't help the engine run cooler on a hot day, it will just run cooler on a really cold day which isn't what you'd want. I'd stick with the 195 degree thermost the computer was programmed around. And stay away from a fail-safe thermostat, they cause more problems from getting hung up wide-open too easily than they solve.
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Old 12-25-2012, 02:37 PM
DC DC is offline
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Yeah Jerry, I got a lot more info on this from a couple of other forums as well as from some additional on-line research. Bottom-line, when the PCM is programmed such that it wants to see 195? as the engine coming up to full operating temperature, it means that anything less is still being looked at as part of the "warming up" cycle, so you're running more rich as well as a couple of other things that you wouldn't continue to want to be happening even though the engine would be at its new 180? operating temperature. The PCM would have no way of realizing the new "set point", so it would definitely be bad news over the long haul.

So, when I did the engine work on my TJ earlier in the year, I definitely went with a new Mopar 195? thermostat.

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