Bad Thermostat?

[dandoc]

So my YJ (Project Salt) is finally back in my possession after a few months of it being garaged (in another state, nonetheless). What I'm noticing now is the engine temperature gauge tops out around 150 degrees F. If I remember correctly, it used to be closer to 200 F. Last year the whole coolant system was drained in order for me to remove the body from the frame; the system was then filled with new coolant and a new drain plug installed. Does this lower temperature gauge reading mean that my thermostat is in need of replacement? If the current thermostat stays in, what ramifications, if any, might I expect? Thanks in advance.

 

[currupt4130]

I'd be happy if I had that kinda drop in temp. I think my YJ runs at 180, never any hotter or cooler.

 

[jps4jeep]

I assume this is the 93 in your sig, should be hotter. the MPI 4.0 needs to be above or around 200 degrees to run properly. run it too cold and the computer will lean out the mixture and the engine might start to knock. Computer controled engines are designed to run optimally in a specific range. I think the 4.0 is 190-210.

 

[jfrabat]

I agree with JPS; as far as I know (and this is for the 4 banger, but I assume it is similar for the 6 cyl), if you run it too cold, the system will not use the reading on your O2 sensor, but rather run in closed loop mode, which makes it inefficient (in other words, your mpg are going down the drain). I would replace it with a Robert Shaw one; these tend to be very accurate temperature wise...

 

[shvlhd666]

Sounds like your thermostat is struck open.

 

[dandoc]

So after doing some research on the 'net (my FSM is at my sister's place in PA), I found that the 4.0L 6 cyl. should have an operating temperature at or near 210 degrees Fahrenheit. Now it's off to the auto parts store for a 195 degree F thermostat!

 

[dandoc]

Today I installed a new 195*F thermostat in the YJ, and all is well again with the engine temperature. Thanks for the added info, guys!

 

[jfrabat]

Glad to hear that...