cooler thermostat

[fast_Z28_guy]

so i've been thinking of swapping to a lower thermostat in the 03 jeep 4L

flipping through several catalogs and online searches...all of them seem to stop at 02 model year.

is there a reason i can't find one for the 03+??

and what is the stock temp for the stat? 195?

would like to run something along the lines of a 180 or possibly a 160 like i run in my Chevys.

thinking of putting an electric fan on the jeep too...to really take advantage of the cooling potential.

 

[jfrabat]

I oput a Taurus fan with the DC Controller on it, and mine runs at around 185* (except on REALLY hot days). Of course, the DC controller has its own radiator temperature probe, so that helps.

 

[Bounty__Hunter]

You run the risk of running too rich and wasting fuel with a cooler thermostat. Could kill your catalytic converter in the long run.

 

[fast_Z28_guy]

on 3 vehicles that i've put a lower stat in...i've yet to see a reduction in gas mileage after the swap.

a cooler engine is more efficient....well...to an extent. it obviously has to be up to operating temp.

15deg lower coolant temps are not going to negatively affect anything, but it has the potential to boost hp slightly, as well as reduce chances of overheating in the south florida heat.


i'm currently running a 160 stat in my camaro...stock is 195...and the coolant temps hold at 175 on the highway....as opposed to 210 normally.

cooler engine means less chance of detonation under heavy load

 

[Bounty__Hunter]

'splain the theory of how the engine runs cooler once up to operating temp? I mean once the thermostat is open, the vehicle theoretically should run at the same temp regardless of what thermostat is in there, right?

A jeep that runs at 210º should run there regardless of what thermostat is uses, correct?

 

[jfrabat]

I've been following this thread with some interest... And I can easily test the theory.

My fan controller allows me to pre-select the temperature I want to keep the radiator at (by means of jumpers). The controller will turn on the fan and adjust its speed to maintain the preselected temperature.

Currently, I am getting 15 mpg on my Jeep, and according to the dash reading (I know, I know, it is not the most exact reading, but it is the only one I got) I am currently runing the Jeep at around 180*.

I will change the setting on the controller to run the Jeep at 210* and test for mileage then, and we can see the difference.

But before thesting, I need to know a couple of things; (1) how should I go about verifying the actual temperature of the radiator? (2) What should be the optimal temperature for the second test run? 210*? On my rig, I guess because of the aluminum radiator, when traveling on the highway with the fan off, the dash reading is about 190~195*, and there will be nothing I could do about that...

Any thoughts, comments or suggestions on this test?

Felipe

 

[fast_Z28_guy]

"'splain the theory of how the engine runs cooler once up to operating temp?"

operating temp is not a specific degree....like 209*. it's a range of temperatures at which the engine is designed to run. hence the reason you have to "warm up" a car in some situations.

and modern computer controlled cars have 2 stages....closed loop at start up in which the engine runs off predetermined settings (fuel/spark etc) untill operating temperature is reached...say 150*
many times this is why an engine idles higher on a cold start...then later drops a few rpm.

once that is reached the computer goes into open loop. at that point it begines to adjust the engine perameters according to sensor readings. things such as A/F ratios from the o2 sensors, MAP sensors, IAT sensors.



as for the "running cooler"
a thermostat adjusts when the coolant is allowed to flow through the block from the radiator. the "operating temperature" is a balance point between the radiators ability to disipate heat and the speed at which the engine circulates coolant.
at the thermostat's designated temperature, the valve on the stat begins to open...but doesn't reach full open untill several degrees later.

i'm basing my discussion on the premis that the radiator has sufficient cooling potential for the particular application. basically a stock jeep radiator WILL NOT be able to dissipate the heat generated by a 1000hp turbocharged 572ci chevy big block.

given an average ambient temperature of air flowing over the radiator (obviously changes if you're in 120deg heat compared to say 80deg) the radiator can disipate a given amount of heat....which is typically enough to keep any engine well below normal operating temp assuming proper circulation.

therefore if the stat is opening at 195*, no matter how much air you're flowing over the radiator, the engine will maintain a temperature of say 15* over the stat temp...210*. if it cools it too much (say its cold outside) the stat will start to close...restricting flow and allowing more of the engines heat to remain in the block. still maintaining that aprox 15* temperature above the stat rating.
so if you put a lower rated stat in there, it will start to open sooner. allowing coolant to flow through the block sooner. the radiator will again disipate the heat and maintain the temperature at aprox 15* above the stat rating.

therefor the engine stat has effectively lowered the operating temperature of the engine.

this is all assuming you are moving air over the radiator.
sitting still or at very low speed the "operating temperature" will depend mostly on the temp at which the radiator fans turn on.

sitting still (with no fan on) a lower stat won't cool the engine any better than the stock unit...since no air is flowing over the radiator to cool the coolant and in turn, the block.

 

[fast_Z28_guy]

my personal experience....albeit not on a jeep....but on 2 different v8 cars...300hp and one at 450hp (in the sig)

all temp readings were seen on a computer scanner...so they are as accurate as you're gonna get. none of this..."well the needle was between 160 and 240" crap.

stock stat was 195*....i installed a 160.
on the road....speeds of say 45+...there was sufficient air circulating over the radiator to maintain a coolant temperature of 210-215*

after installing the lower stat and doing the same driving, the coolant temperature ranged from 175-180*


now with the lower stat and idling:
sitting in the driveway the temperature would quickly climb to 220* before the coolant fans would turn on. they would remain on untill the coolant temp wsa at apoximatly 210* and then shut off. the temp would cycle between 210* and 220*+ due to the setting of the fans.

now...i also had a fan switch installed on the car. giving me the option of manually running the fans at 2 speeds...low and high. sitting in the driveway...watching the scanner....with the fans switched to LOW. the coolant would hover at aproximatly 175-180*...just like when driving. however if i flipped to HIGH the coolant would drop to between 170-175* due to the increased air over the radiator (imagine running 850rpm at 60mph...not much heat generated).

 

[fast_Z28_guy]

according to the dash reading (I know, I know, it is not the most exact reading, but it is the only one I got) I am currently runing the Jeep at around 180*."

is this while sitting still? cause then the fans should be on right? i would think to get that low...they would have to be.


"On my rig, I guess because of the aluminum radiator, when traveling on the highway with the fan off, the dash reading is about 190~195*, and there will be nothing I could do about that.."

if the fans are off...the temperature is determined more by the thermostat than the radiator (assuming the radiator is up to the task). because regardless of the radiator...even if it can cool a topfuel dragster motor....if the stat is restricting coolant flow to the engine...it won't have a noticable affect on the coolant temp and engine temp.

if you installed a 160* stat in the engine....i'll bet money that you're highway temps will be reduced considerably.

 

[jfrabat]

according to the dash reading (I know, I know, it is not the most exact reading, but it is the only one I got) I am currently runing the Jeep at around 180*."

is this while sitting still? cause then the fans should be on right? i would think to get that low...they would have to be.

Yup, I am talking about standing still. Now, I dont know exactly what Stat I have, but if I turn the fan manually on (overriding the automatic controller), the temp will go even lower than that. I should point out that I am not sure if the dash temp is read at the engine or at the radiator... I have not looked to verify that, and I have minimal knowledge on car mechanics.

"On my rig, I guess because of the aluminum radiator, when traveling on the highway with the fan off, the dash reading is about 190~195*, and there will be nothing I could do about that.."

if the fans are off...the temperature is determined more by the thermostat than the radiator (assuming the radiator is up to the task). because regardless of the radiator...even if it can cool a topfuel dragster motor....if the stat is restricting coolant flow to the engine...it won't have a noticable affect on the coolant temp and engine temp.

if you installed a 160* stat in the engine....i'll bet money that you're highway temps will be reduced considerably.

Probably so. Maybe that is not a bad idea to do, since I am currently in Miami, FL, and when I take the Jeep to Panama, the heat will only get worse (there are only two seasons in Panama, the hot season, and the new year's eve!).

Felipe

 

[fast_Z28_guy]

if it's pulling the temps down that low....you either have a low temp thermostat...probably a 160 or your guage is way off.

i would think your highway temps would be lower than if the car was sititng still.

although how long do you have it stopped before it starts going over 180?



easy way to check what stat you have is to remove it. some will say wht they open at...others will have to be tested.
basically put it in a pot of water with a candy thermometer (or some kitchen thermometer that reads over 200*) and bring the water to a boil. when the valve starts to open...that's the rating.

it's also possible someone removed the stat altogether...which is actually WORSE for the engine.

 

[jfrabat]

I'll have to check then... This jeep was 12 years old when I bought it, and I have found MANY things were replaced in those years (most for some not so good quality products!)

Felipe

 

[jfrabat]

While driving home, I took a picture of the temp reading (this is as I was getting off the highway). After I parked at home, I let the jeep idle (OK, so mayble I gave it a little gas to get the temp up, but you get the idea!) to see how high the temp would get before the e-fan would kick in and keep it steady. Here's what I got:

By the way, please excuse the poor quality, but they were taken with a phone camera while driving. Here's the highway reading:

And standing still it looks like this:

For your reference, the highway drive home is about 8 to 9 miles, and the day was really crappy roday (drizzling rain and 75* outside, making it a cool day for Miami standards). Let me know what you think.

Felipe

 

[fast_Z28_guy]

wow that guage is very strange.

starts at 100, ends at 260....yet 1/2 way is 210 instead of 180.

basically who knows what the true reading is.

but since its that low...i'd be willing to bet it either has a low stat in it....or someone pulled the stat out completly.

alot of guys who have problems overheating pull the stat out, which can actually cause more problems. first off if the engine is overheating it is because something is wrong...and tricking the engine into flowing more coolant is not the way to solve that problem.
second i've been told (no engineering proof of this) that the without the stat in, the coolant flows through the block at too high a rate. basically it's flowing so fast that it doesn't give adequate time to draw heat out of the block. so even though the coolant reading is low, the block may actually be hotter than it should be.


i say pull your thermostat and see what you have.

 

[jfrabat]

Yeah, I guess I'll have to check that as well... To be honest, I dont even know where the stat is, but I'll look it up in my manuals and see what's going on.

 

[fast_Z28_guy]

found some random info today while looking through a catalog...

quadratec lists 97-04 jeeps as having a 195* stat...which i kindda figured. didn't list anything for earlier...but i'm guessing its similar.

and judging from the pictures of the engine (jeep isn't here...so can't pop the hood), the stat is on the very front of the cylinder head. it is housed under a 90* goose-neck which should have a big coolant line running to it.


in order to actually get to the stat...you'll have to drain a little of the coolant.

 

[Utah_jeepster]

It has taken me awhile to talk with my partner about this issue an, ASE mechanic who specializes in newer computer controlled vehicles.

So according to him if you attempt to source some after market thermostat to run your jeep with a lower opening point of 195 you will face two major problems.

The jeep is designed to run normal at 210 to completely burn all the fuel in the combustion chamber. if your lower the thermostat the O2 sensor will inform the computer that you still have a higher than normal O2 reading across the sensor and will keep the throttle body slightly closed in a attempt to warm up the motor to normal operating temp. Sending a slightly elevated amount of carbon build up to your catalytic converter thus reducing its life considerably.

If your computer reads this over 5 times (motor on cycle) with a operating time of over 20 minutes or so (he was not sure what the time out was on this error) it will send a non-fatal code (safe drive home) alerting you that your thermostat is stuck open.
It is taking five sensor/timer inputs to come to this conclusion, the mass air sensor telling it the volume of air passing it, the throttle body position sensor telling the computer how wide its opening, the water temp sensor, the O2 sensor telling it how much oxygen/ carbon dioxide is in the spent gas, and a built in timer telling the computer how long the vehicle has been on during this cycle.

He said you might want to try a 175 degree thermostat and see if your jeep will take it but keep a 195 available if your get a check engine light.

 

[mud4feet]

It has taken me awhile to talk with my partner about this issue an, ASE mechanic who specializes in newer computer controlled vehicles.

So according to him if you attempt to source some after market thermostat to run your jeep with a lower opening point of 195 you will face two major problems.

The jeep is designed to run normal at 210 to completely burn all the fuel in the combustion chamber. if your lower the thermostat the O2 sensor will inform the computer that you still have a higher than normal O2 reading across the sensor and will keep the throttle body slightly closed in a attempt to warm up the motor to normal operating temp. Sending a slightly elevated amount of carbon build up to your catalytic converter thus reducing its life considerably.

If your computer reads this over 5 times (motor on cycle) with a operating time of over 20 minutes or so (he was not sure what the time out was on this error) it will send a non-fatal code (safe drive home) alerting you that your thermostat is stuck open.
It is taking five sensor/timer inputs to come to this conclusion, the mass air sensor telling it the volume of air passing it, the throttle body position sensor telling the computer how wide its opening, the water temp sensor, the O2 sensor telling it how much oxygen/ carbon dioxide is in the spent gas, and a built in timer telling the computer how long the vehicle has been on during this cycle.

He said you might want to try a 175 degree thermostat and see if your jeep will take it but keep a 195 available if your get a check engine light.

Gotta love those computers!! I'm waitin' for 'em to tell me when to wake up in the morning...............I know it's coming!!!! :lol: :lol: :lol: :lol: :lol: :lol:


I'll just keep runnin' the stock 'stat..........don't think changing it will increase my little 4banger horses that much anyway.

 

[fast_Z28_guy]

while in theory i think your description of the what the computer does is correct.

but i find it VERY hard to believe this could happen by lowering the temps 15 or 25 deg.

but thanks for the info

 

[jfrabat]

Just to be sure, I am replacing my thermostat with a Robertshaw 195 Degree Thermostat... I figure for $15 (including shipping), I may as well be sure the darn thing is working right!

Worst case scenario, the Jeep continues to work as it has in the past. Best case scenario, I get more mpg.

Felipe