'00 XJ 270K miles

So, I have read a lot on this forum on what is the best thermostat to use for your XJ and the majority agreed to go with the stock 195* thermostat. Currently, I have a 160* thermostat and I know that most people on this forum are against it due to the fact that this temperature is considered low for an XJ.

The problem is that where I come from the weather temperate is normally over 120F that’s why most people here prefer the 160* thermostat. My XJ rarely reaches 210* unless I am in traffic with the AC on (obviously) it starts to crawl up slowly. By the way, I replaced every component in the cooling system.

So, the question is do you think I should go with a higher degree thermostat or just stick with this setup. I am planning on either going with a 180* (mishimoto) or a 195* (stock) thermostat.

 

180 is the minimum you should go, some XJs with the tow package came with one from the factory.

 

A factory Mopar thermostat in 195* will be fine.

 

The thermostat does not set the running temperature of the engine. It only determines the temperature at which your t-stat begins to open. Once it's fully open, the running temperature of your engine is a complex dance between several factors, but the T-stat is no longer an influence.

A lower t-stat rating will allow the coolant to circulate sooner, making your engine take longer to get up to normal operating temperature. This keep your engine running in open circuit longer, which means you will run richer for a longer period, which is not really good for your engine.

If you drive almost all very short runs, a lower t-stat will keep your engine cooler, but only for short runs. Again, this is not really a good thing.

We have several members who live where temps are often 120. They have no problem with a 195 t-stat.

 

All good advice.

I once saw a graph in a car manual way back in the day. It summarized numerous tests Ford did with engines on test stands. They tested engine longevity vs operating temps and put them in a graph/chart. What it plainly showed was an upside-down j-curve that illustrated a decrease as an engine went below 192 and became more precipitous as constant operating temps dropped below 180*. These were constant running temperatures ...as in low temp and no theremostats. These tests were done in the 60's so, yeah, it was a while ago. But it always stuck with me. I have no idea what book I saw them in or I'd love to share them. I guess you'll have to take it for what it's worth, but the key thing is how important it is to keep your engine within it's 'engineered' operating temperature.

 

Bingo.

 

somewhat like the above.
I have dismantled engines that are known to run uneven temps front to back and its usually the coolest ones that have the most pronounced ridge bore