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Is a 180 tstat gonna do harm?

M

MattS

NAXJA Forum User
Location
Danville, VA
After a lot of hit or miss stuff trying to figure out overheating issues. It turned out that my radiator was clogged/shot after a flush. I won't go into that. the guy that did it put in a 180 tstat instead of the 195. I keep reading arguments for using and not using a 180. What is the consensus? Am I going to have problems using it? I am running great now, for what it's worth.
 
what year?

it depends on whether the engine gets to the correct operating temp.

if the engine runs between 190-210 degrees than its ok. if the engine is running too cool, than its a problem.

ive only run a 195 in my 89 and not hasve had any problems.

i do know that when the thermo on my 89 gets warn out and opens too soon or stays open too long because of a weak spring, it runs too cool and i get crappy gas mileage. my 89 gets alot better gas mileage the hotter the engine and outside temp gets.
 
MattS said:
Sorry, it's a 99 XJ.
Click to expand...

i would say to put in a 195 since you found the problem with the radiator.

running too cool can cause internal engine wear and for a 10$ part, it isnt worth it in the long run. my understanding is that the hotter it runs, the better emmissions it produces, and the cooler it runs, the more power you get with less mpg.

also, the obd2 can be pretty picky.
 
I run a high flow 180 degree tstat. It runs cooler until you get to highway speeds for a few minutes, then it's at 210. During the summer it's 210 and 225 on the highway. Basically it just takes a little longer for it to get to operating temp.

I've read here that it doesn't hurt the gas mileage.

I did not see my gas mileage change. I also run a CSF 3 core radiator.
 
A lot of guys are running cooler stats but a "few" of them are doing so in the attempts to remedy a cooling/heating problem. Not a good strategy. My 2 cents? Jeep engineered the 4.0 engine for a 195 stat for a variety of reasons. I have a stock engine and will continue to run the recommended 195 stat.
 
Too cool a t-stat will result in the engine thinking it's still warming up, and stay in open loop operation. The O2 sensor will not be 'in' the loop, and the engine will run rich, hence the poor MPG. The cooler exhaust also will not burn-off the contaminants in the cat, made worse by the rich mixture, so you can see how the low temps can be a problem. Some years ago I had to pull the head off my '92 4.0 to replace the lifters. While off, I did some cleaning and scraping, and the coolant passage at the back of the head was almost completely clogged. I cleaned it, and the corresponding passage in the block, and since then, have never had a temp issue. It wasn't a hot runner before, but now, even if stuck in traffic on a hot day, will not go above it's normal temp. I know that yanking a head is drastic. but more than likely a clogged head, or some other coolant- flow impediment is likely the culprit.
 
I've done everything except the fans. Well I replaced the clutch a couple of years ago, and it still doesn't stay as cool as when it was original.
 
What a thermostat does is determine when the coolant begins to flow through the radiator and it also determines how quickly the engine will reach normal operating tempurature ....and that's about it. Warm up time on a smog controlled eninge is a relatively "dirty" event and the faster the engine gets up to operating tempurature, the faster all of the normal emmissions controls will function ...hence the 195deg t-stat. The temp rating of the t-stat is when it *begins* to open; they are not fully open until the coolant is quite a bit hotter. Will a 180 t-stat cause any problems in your XJ? Nope. Will your engine warm up just as fast? Yup. Will your engine *potentially* run cooler with a 180 t-stat? Yup.

In most vehicles the 195 t-stat isn't a problem but on the XJ the radiator and, more importantly, the flow of air *through* the radiator are somewhat compromised. The relatively small size of the radiator is limited by the design of the vehicle and the airflow, or lack thereof, through the radiator is a function of stuffing that *long* inline six into a space that should be occupied with a V-6 or I-4 engine. Take a look at how the area immediately behind the radiator is jammed with the engine, accessory drives, AC fan, etc ...all this stuff effectively blocks the airflow through the rad. Tack on a cooling system that's been neglected and you've set yourself up for a hot running engine. I'm sorry but IMHO, 210deg is just way too hot for an engine to run under normal conditions; and it doesn't take much to get the engine running hotter with the stock system. I think the AMC engineers made a big compromise on cooling so they could use their legacy six-banger motor (instead of those hideous GM 2.8L V-6's).

Here's my system:
2-core Readi-Rad "Heat Buster" radiator
Flow Kooler high flow water pump
180 deg flow balanced/hi-flow RobertShaw T-Stat
seperate mount tranny coooler.

4.0L six now runs about 25-30deg cooler (based on dash gauge) and will only reach 210 on the hottest days with the A/C on. Mileage hasn't suffered and it smog checks fine.

Mike
00XJ
 
For what its worth, according to my temp gauge my coolant temp never gets over about 160. According to the guy I bought it from it has a high flow water pump and a 3 row radiator but not sure about the t-stat. Heater still works fine and it gets up to 150-160 within 10 minutes of driving. Also had no problems passing emissions. I really don't think a 180 deg t-stat will hurt anything unless you have other problems already.
 
jester4x4 said:
For what its worth, according to my temp gauge my coolant temp never gets over about 160. According to the guy I bought it from it has a high flow water pump and a 3 row radiator but not sure about the t-stat. Heater still works fine and it gets up to 150-160 within 10 minutes of driving. Also had no problems passing emissions. I really don't think a 180 deg t-stat will hurt anything unless you have other problems already.
Click to expand...


you are probably barely running within open loop mode, if you are at all. The motor was designed to run right around 210. I have a 3 core, new water pump, new thermo, and I stay pinned on 210. I have run it cooler, I got wore mileage, less power, and more emissions(exhaust had a stinkier smell to it). I would say to try putting a 195 thermo in, to see if you notice any difference
 
jocko463 said:
What a thermostat does is determine when the coolant begins to flow through the radiator and it also determines how quickly the engine will reach normal operating tempurature ....and that's about it. Warm up time on a smog controlled eninge is a relatively "dirty" event and the faster the engine gets up to operating tempurature, the faster all of the normal emmissions controls will function ...hence the 195deg t-stat. The temp rating of the t-stat is when it *begins* to open; they are not fully open until the coolant is quite a bit hotter. Will a 180 t-stat cause any problems in your XJ? Nope. Will your engine warm up just as fast? Yup. Will your engine *potentially* run cooler with a 180 t-stat? Yup.

In most vehicles the 195 t-stat isn't a problem but on the XJ the radiator and, more importantly, the flow of air *through* the radiator are somewhat compromised. The relatively small size of the radiator is limited by the design of the vehicle and the airflow, or lack thereof, through the radiator is a function of stuffing that *long* inline six into a space that should be occupied with a V-6 or I-4 engine. Take a look at how the area immediately behind the radiator is jammed with the engine, accessory drives, AC fan, etc ...all this stuff effectively blocks the airflow through the rad. Tack on a cooling system that's been neglected and you've set yourself up for a hot running engine. I'm sorry but IMHO, 210deg is just way too hot for an engine to run under normal conditions; and it doesn't take much to get the engine running hotter with the stock system. I think the AMC engineers made a big compromise on cooling so they could use their legacy six-banger motor (instead of those hideous GM 2.8L V-6's).

Here's my system:
2-core Readi-Rad "Heat Buster" radiator
Flow Kooler high flow water pump
180 deg flow balanced/hi-flow RobertShaw T-Stat
seperate mount tranny coooler.

4.0L six now runs about 25-30deg cooler (based on dash gauge) and will only reach 210 on the hottest days with the A/C on. Mileage hasn't suffered and it smog checks fine.

Mike
00XJ
Click to expand...


X2, X2, X2!!!! yah, what he said! I agree 100%, I have had the same experience, I have run 160 F, 180 F and 195 F thermostats with no differences, except engine running cooler. Mine ran fine in closed loop with no problems even with a 160 F thermo.

That said, mine are all 87-90 Renix jeeps. While I think 180 F is fine for a 99, I have not tested it. But if yours running fine with a 180 F, no OBD-II codes, I would leave it alone. IF it ain't broke don't fix it!
 
heyhar said:
Too cool a t-stat will result in the engine thinking it's still warming up, and stay in open loop operation. The O2 sensor will not be 'in' the loop, and the engine will run rich, hence the poor MPG. The cooler exhaust also will not burn-off the contaminants in the cat, made worse by the rich mixture, so you can see how the low temps can be a problem.
Click to expand...

Not true. (I disagree!).

The O2 / computer systems shift into closed loop in less than a minute of start up. The Jeep (XJ) O2 sensors all have an electrically operated internal heater that gets them to proper operating temperature, usually in seconds of engine start up. Once that O2 sensor is heated by the internal electric heater element the computer tests the O2 sensor and shifts into closed loop mode. I have verified this with engineers at the factory and with my own on board testing.

Now if for some reason your O2 sensor heater is not working, or not getting voltage to the internal heater, thermostat selection (the hotter the better) will affect gas mileage, but it is not the optimal fix for an O2 sensor problem.

Sounds to me like your results indicate an O2 sensor problem!!!!!

I have run a 160 F for 2 years, a 180 F and recently in my second XJ a 180 F and 195 F thermostat, with no observed differences in mileage due to the thermostat temperature selection.

For Renix Jeeps 5-90 and I recommend 180 F thermostats.

I done have any OBD-II jeeps, but it sounds like 180 F is OK in the OBD-II systems as well.
 
wolfpackjeeper said:
you are probably barely running within open loop mode, if you are at all. The motor was designed to run right around 210. I have a 3 core, new water pump, new thermo, and I stay pinned on 210. I have run it cooler, I got wore mileage, less power, and more emissions(exhaust had a stinkier smell to it). I would say to try putting a 195 thermo in, to see if you notice any difference
Click to expand...

I have been thinking about doing that anyway to try to get better mileage. I only have 31s right now and if my speedo and odometer are right (which i doubt they are due to the tire size) I am only averaging about 13-14mpg
 
How does running a 180* thermostat run cooler? Obviously the coolant is going to start to circulate through the engine faster, thus cooling the engine faster in theory. However becuase the coolant circulates faster it doesnt have ample time in the radiator to cool which inturn actually makes it hotter.
 
The Lure Washer said:
How does running a 180* thermostat run cooler? Obviously the coolant is going to start to circulate through the engine faster, thus cooling the engine faster in theory. However becuase the coolant circulates faster it doesnt have ample time in the radiator to cool which inturn actually makes it hotter.
Click to expand...

The 180* T-stat will just delay the time it takes to get up to operating temperature. I had an old Jeep with a chronic leak, and I ran it without a thermostat at all during the summer, and it would still eventually get up to 210*.

The flow rate is basically controlled by the water pump, and the thermostat simply regulates how much of that flow is diverted to the radiator. You are right, if the coolant flows too quickly through the radiator, it will not cool down enough, and the engine can over-heat.


In regards to the original question, optimal operating temperature for a gasoline engine is 195-210 degrees. It should get the best economy and emissions in this range. Too hot, and you're NOx emissions will go up and you risk damage from detonation. Too low, and cylinder temperatures won't be sufficient for complete combustion, also leading to higher emissions as well as poor fuel economy. I would stick to the 195 degree thermostat.

Lower temperature thermostats are designed for engines that need extra cooling capacity due to modifications that generate more heat. But then again, a hotter engine and a cooler thermostat won't do much unless the radiator and cooling system pressure are also changed appropriately to accommodate the extra generated heat. Cooling systems are have to be engineered to reach an appropriate equilibrium at the desired operating temperature.
 
i dont know if jeep planned on every jeep owner to run 31's or 33's and drive the thing overfull with gear including beer and ammo for hours on end up mountains in the hot ass summers here in CA, so i figured a 180 t stat is fine. if i dont turn on my fan for the engine it gets pretty hot up to 200 quick enough, ill leave it there if it gets too hot. maybe run a switch from your cooling fan to the dash if your super worried?(use a good relay)
 
After reading this I am wondering if I have a 180 degree tstat. Where is 195 degrees on the gauge on the dash? In relation to 210 (top dead center).

I bought my 98 Cherokee in the spring and I know the tstat was changed right before I bought it. The needle sits just above the second line (about 1/4) on the gauge.

During the summer it I had great fuel mileage and the temperature would be a little below 210. Now that it is colder (I live in Ottawa) the needle rarely moves from just over 1/4. My fuel mileage has gone way down too.
 
I bought a 195 tstat today for $7.99. I pulled the old (9 months old) tstat out that was installed by the previous owner. Guess what? It was a 160. December in Ottawa means the Jeep was running at 160 all the time. It always ran around 200 in the summer, but the colder air would't let the Jeep warm up anymore than 160.

I installed the new one, let the jeep warm up in the driveway and took it for a spin. Within 100 feet of my laneway I could feel a difference. It just seemed to run smoother. Lets see if this cures my shitty mileage problem that only started when the outside temperature dropped in the fall. As an added bonus, the heater blow much hotter air.

I don't understand why anyone would run anything but what is suggested for their vehicle. If you have an overheating problem, running a 160 or 180 may only slow down the amount of time it takes to overheat.
 
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