Advantages of using lower temp thermostat?

I'm about to help a friend of mine replace his radiator, hoses and thermostat. While researching, I noticed most recommend sticking with the OEM temp thermostat. I came across this online article about upgrading the cooling system on an XJ: http://www.4wdandsportutility.com/tech/0708_4wd_1997_jeep_cherokee_cooling_system/photo_11.html

Its suggests going with a 180 degree thermostat for improved fuel economy, and a 160 degree for performance. Anyone have opinions on this? Any downside to going with a lower one?

I doubt you'll notice any improved fuel economy with the 180. Plus, the XJ's cooling system will struggle to maintain 180 degrees anyway. Even if you go with the biggest, fanciest radiator and upgrade the fan clutch or go with dual electric fans, I don't think it could do 180 degrees. One downside is less heat output for the HAVC system, but living in Florida thats probably not a concern for you. What kind of radiator is your replacement?

Go no lower than a 185..At 180 i got crap MPG, but at 185 i'm back to 18/20MPG..I live in the desert an my xj runs 190no AC and 200 with the AC on..It is all stock cooling system(89 closed). Summer temps are around 100 to 115..

Mine gets serviced every 2 years at the rad shop..

Ya, that article goes against most of the information you will find on here. Everyone on here will tell you to stick with the oem 195* thermostat to get the best performance and mpg. Otherwise the engine will begin to run lean to get you up to temperature, like it does in start up mode, but the thermostat will fight you on that.

Ian Christiansen said:

I doubt you'll notice any improved fuel economy with the 180. Plus, the XJ's cooling system will struggle to maintain 180 degrees anyway. Even if you go with the biggest, fanciest radiator and upgrade the fan clutch or go with dual electric fans, I don't think it could do 180 degrees. One downside is less heat output for the HAVC system, but living in Florida thats probably not a concern for you. What kind of radiator is your replacement?

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He is low on $ so he picked up a newer radiator from a salvage yard. Everything else will be new though.

Thanks guys, for the good advice.:thumbup: Looks like we will stick with the OEM temp stat.

That article was nothing more than an advertisment for various vendors and a Chrysler dealership. The writers didn't even do the work themselves. And then the kicker, "With parts in place, we noticed an obvious power improvement, chiefly due to the fact that our cooling system was performing as intended." Please... What a joke. I guess if it was a POS system beforehand and continually overheating they may notice a "performance" improvement. Otherwise, they're just trying to convince people they need to run out and buy all this crap and install it.

Bottom line is the factory parts when maintained properly perform just fine. Thermostat included.

Advantages of running a cooler thermostat:

Longer warm up times, so you will run richer longer and burn more fuel.

IF you have an over-heating problem fix the system. Adjust your coolant mix--50/50 makes a pretty good antifreeze in all but the most extreme conditions, but it SUCKS as a coolant. From late Spring through early Fall--the non-freezing season (adjust for local conditions)--you should run 30 ethylene glycol and 70 distilled water for COOLING.

XJPaul said:

http://www.4wdandsportutility.com/tech/0708_4wd_1997_jeep_cherokee_cooling_system/photo_11.html

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Wow. Now that was entertaining.

joe_peters said:

Advantages of running a cooler thermostat:

Longer warm up times, so you will run richer longer and burn more fuel.

IF you have an over-heating problem fix the system. Adjust your coolant mix--50/50 makes a pretty good antifreeze in all but the most extreme conditions, but it SUCKS as a coolant. From late Spring through early Fall--the non-freezing season (adjust for local conditions)--you should run 30 ethylene glycol and 70 distilled water for COOLING.

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Not overheating...leaky radiator. He bought his XJ a few months ago and is just replacing things as needed. Figured we would do the t-stat and hoses as well. Gonna go with the Stant Superstat to make you proud. Thanks all, for the great feedback!
:cheers:

Advantages of running a cooler thermostat:

... Is getting coolant flow happening sooner.

Coolant entering the radiator at 195' ... leaves the radiator at about 180'

Coolant entering the radiator at 185' ... leaves the radiator at about 170' ... which gives the thermostat some cooler temp liquid to play with when dealing with the hot liquid temps generated by the engine.

............ all depending on cooling system efficiency of course
As the radiator is a heat exchanger ... not a refridgerator that forces temps down to a minimum preset temp.

Lower temp thermostats are NOT an overheating fix ..... but they can be used to gain a slight advantage in maintaining a constant operating temp ... depending on operating conditions.

Its nigh on impossible to get the 4.0l XJs running temp down to a constant, low temp due to the size of the radiator and the small engine bay.

The best Ive managed is a constant 195' in operating temps of 30' to 110'+ for the past 12mnths.

That is with;
A 2row copper/brass radiator, (always used 2row factory aluminium/plastic before)
30/70 coolant mix ( less actually - due to local ambient temps),
Separate AW4 oil cooler,(always relied on the useless factory system before)
Heavy duty fanclutch,(always fitted a std factory one before)
1/2" bonnet spacers & induction blocker.

.... and a thermostat that is 1/4 open at 195' ... and fully open at 205'.
Its sold here as a 195' thermostat but performs probably, similiarily to what a U.S. 188' thermostat does.
By comparison ... the factory thermostat starts to open at 195' and is fully open at 220'.

The XJ thermostat is NOT some special item either ... Its just a common ol garden variety thermostat that fits a variety of vehicles and comes in a bunch of temp ranges .... brand quality is probably the most important issue ...

Ive tried 180' thermostats ... made very little difference to fuel use ... but OBDII goes closed loop at 65' and the factory service manual mentions 160' is a satisfactory warmed up temp anyway ..... and the temps still spiked under load due to the inefficiency of the cooling system size ...

Longer warm up times are not usually an issue ... unless your climate is the cause, with ambient temps regularly under about 65'.
Take note of joe_peters "Spring thru Fall" comments as an example.

If anyone wants to play with thermostat temps to see if they get a stable improvement ... I would suggest trying some of the ones from 182' up to 192' ... along with an efficient radiator and fan.

As for that article ...

160' & 180' thermostats being recommended ???? ... by some mob that did a cooling system upgrade ... and left the dinky little light duty, original, fan clutch in there ???

I would be reading a few more articles as comparisons I think ....

Some good points, thanks.:thumbup: Research?...yes, I definitely like to get as much info as possible so I do the job right the first time.

carves said:

Its nigh on impossible to get the 4.0l XJs running temp down to a constant, low temp due to the size of the radiator and the small engine bay.

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Define "low"

The best Ive managed is a constant 195' in operating temps of 30' to 110'+ for the past 12mnths.

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There is absolutely NOTHING wrong with that temp.

Why are people so afraid to let these things run at 195-210? Heat makes power, boys!

I've been running a 160 for a couple years now... in the summer. In the winter it's too cool for the heater to get hot. But in the summer I love it. I have a completely stock, well maintained cooling system and it has no trouble staying cool. However, it won't go down to 160 because my aux fan hardly ever comes on (I need a fan controller for a 160 degree t-stat). I did it to help out intake air temps for performance. I didn't notice any difference in mpg's and not much of a performance increase but my IAT's are a little cooler so I'm sure there's a minute performance gain, I just can't feel it.

Like carves said, 160 degrees well above what's necessary to get into closed loop and it doesn't take any longer to get there so warm up time, running rich, bad mpg's isn't an issue.

All this talk about running cold...

Anyone ever think about letting things get hot enough so that the engine oil burns off whatever moisture forms in it? Let them run cold and sludge up. Ya, that sounds great!

Again, if you need to run a 160 tstat to stay "cool", then you have something else wrong. Fix the problem and let it run at 195.

You do realize that 160 refers to the coolant temp not the combustion chamber temp right? 40 degrees coolant temp difference isn't going to make very much of a difference in the "operating temp" of the combustion chamber at all.

There's nothing wrong with running cooler than 195. 160 is cooler, but certainly not "cold". Also, my valve train and combustion chambers stay clean as a whistle running a 160 t-stat.

Milford Cubicle II said:

You do realize that 160 refers to the coolant temp not the combustion chamber temp right? 40 degrees coolant temp difference isn't going to make very much of a difference in the "operating temp" of the combustion chamber at all.

There's nothing wrong with running cooler than 195. 160 is cooler, but certainly not "cold". Also, my valve train and combustion chambers stay clean as a whistle running a 160 t-stat.

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What? Combustion temps are higher than the tstat temp? Seriously...

40 degrees in coolant temp is going to have an affect on oil temp though. Go back and re-read my post. Where did I say anything about combustion temps? Talk about going off on a tangent...

Sorry, didn't seem to sound like I was on a tangent. And it seems like people seem to think a 160 t-stat will make a difference in how your engine "runs" when it won't really make any difference at all, more or less just the temp that it operates at.

But I disagree with you about the oil. I'm not sure how a 40 degree coolant temp change translates into oil temp difference but I seriously doubt it's enough to hurt anything. I haven't found that running oil coolers cause sludge build up or any other negative effects on the oil and I'm sure an oil cooler cools the oil more than engine coolant does. Right? :dunno:

I think you're forgetting about the coolant temp sensor and the PCM.

What about it?