I've been searching the forums regarding opinions about a 180* t-stat, and I happened to notice that several members list 210* as wide open. I don't know if it makes a difference about whether or not to use a 180* one, and not to nitpick, but the true wide-open temperature for an XJ is 218* (check a Mitchell Manual--I don't trust Haynes or Chilton's due to far too many mistakes on technical issues). The electric fan is programmed to come on at exactly 218* and shut off at exactly 209*. Considering this, it would seem that the 180* t-stat WOULD make a difference. Any opinions?
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Correct wide-open t-stat temp.
- Thread starter Timber
- Start date
My only concern would be that the engine run too cool. If I recall correctly, the 4.0 is designed to run a little warmer. Hence, the standard thermostat is 195. If you have to go with a 180, is it not just masking the real problem, namely deficiencies in your cooling system?
BSD
BSD
If you are running around 210 - perhaps a little higher at stop - then I would not worry about it. About the most effective cheap performance upgrades I can think of - beyond good maintenence - are a good KN filter and dropping the air temperature coming into the throttle body. THis later item makes for denser air. I have seen several people do this and one fellow posted a fairly good technical evaluation of the process. It basically entails wrapping the air box and breather tube in insulated reflective tape. Another basic mod in this vane is increasing the gap at the back end of your hood - done with a couple of thick washers as spacers - so that the air flow in your engine compartment is better.
8Mud
NAXJA Forum User
- Location
- Central Germany
People forget the purpose of the thermostat is to keep a constant (engineered) temp. in the motor. While the temp. in the motor isn´t uniform, it is usually optimum (within reason), for emissions and function, in a fairly narrow envelope.
Thermostats regulate the motor temp and flow and are often some different than the advertised parameters (fairly primative). Have rarley found two that worked exactly the same, plus or minus (average) of five or more degrees. I do a lot of work with heat exchangers and can picture temp. curves fairly accuratly in my minds eye (I watch the temp. gauge cycle).
On the Renix, the temerature sensor, for the computer, keeps the ECU in open loop (high idle/rich) until about 140 F and imputs timing advance and pulse band width for the injectors, in relation to motor temp.
A 180 degree thermostat, could possibly , dump relatively low temp. coolant into the top of the radiator, there is typicaly a 30-40 degree drop in temp. between the in and out of the radiator (depending on air temp, flow and humidity). Possible the coolant exiting the radiator, could cause the motor to switch from open, to closed loop and be too cool for proper motor function (at night or a cool day). The temp. sensor (for the ECU) isn´t very far from the water pump.
A better way to increase cooling, would be a larger radiator, increased air flow and/or proper function of exisiting componenets. Let the thermostat do it´s job and keep the motor at (or near) the proper temp.
I have lowered my thermostat to 190, with no seemingly ill affects, but then again no great improvement either. Tried a 185 (curious) flunked an emission test, plugs were a bit sooty and the exhaust stunk. Renix seems kind of emission borderline, from the manufacturer, doesn´t take much to make them miss the envelope.
Thermostats regulate the motor temp and flow and are often some different than the advertised parameters (fairly primative). Have rarley found two that worked exactly the same, plus or minus (average) of five or more degrees. I do a lot of work with heat exchangers and can picture temp. curves fairly accuratly in my minds eye (I watch the temp. gauge cycle).
On the Renix, the temerature sensor, for the computer, keeps the ECU in open loop (high idle/rich) until about 140 F and imputs timing advance and pulse band width for the injectors, in relation to motor temp.
A 180 degree thermostat, could possibly , dump relatively low temp. coolant into the top of the radiator, there is typicaly a 30-40 degree drop in temp. between the in and out of the radiator (depending on air temp, flow and humidity). Possible the coolant exiting the radiator, could cause the motor to switch from open, to closed loop and be too cool for proper motor function (at night or a cool day). The temp. sensor (for the ECU) isn´t very far from the water pump.
A better way to increase cooling, would be a larger radiator, increased air flow and/or proper function of exisiting componenets. Let the thermostat do it´s job and keep the motor at (or near) the proper temp.
I have lowered my thermostat to 190, with no seemingly ill affects, but then again no great improvement either. Tried a 185 (curious) flunked an emission test, plugs were a bit sooty and the exhaust stunk. Renix seems kind of emission borderline, from the manufacturer, doesn´t take much to make them miss the envelope.
BillR
Toy Jeep driver!
- Location
- Flagstaff, AZ
I currently run a 180* Jet t-stat. It was recommended when I installed the Stage2 Jet chip, as the engine will run a little hotter with it. I drilled the weep hole and installed it.
Mine runs great. I still get around 16mpg in-town with my setup. On the freeway on a hot day, the guage shows about 200*. At slow speeds, it's right at 210*. We don't have emissions testing, so I don't know how that's affected.
I'd like to see some FIRM data as to what the engine ECU thinks is COLD for closed loop operation. I've heard several different temps between 160* and 200*.
All I can tell you is mine runs fine and gets good mileage for what it has on it.
Mine runs great. I still get around 16mpg in-town with my setup. On the freeway on a hot day, the guage shows about 200*. At slow speeds, it's right at 210*. We don't have emissions testing, so I don't know how that's affected.
I'd like to see some FIRM data as to what the engine ECU thinks is COLD for closed loop operation. I've heard several different temps between 160* and 200*.
All I can tell you is mine runs fine and gets good mileage for what it has on it.
Dr. Dyno
NAXJA Forum User
- Location
- Al Ain, UAE
BSD said:
That was me
:http://jeep4.0performance.4mg.com/ramair.html
The true figure's about 165*F or 75*C. I've been running a 180* t'stat on my XJ for the last seven years with no adverse effect on gas mileage and emissions. I have a Robertshaw 180* t'stat on my stroker.
Keep in mind though that I live in a hot climate where even the daytime temp. in winter rarely drops below 60*F. If you live in a cool temperate climate, stick with a 195* t'stat. If you live in an Arctic type climate where it rarely exceeds 60*F even in mid-summer, go for a Robertshaw 205* t'stat so that the engine warms up faster and the heater works better.
____________________________________________
1992 XJ Laredo 4-dr - 4.6L I6 HO Stroker - 177k miles - AX15, NP231, D35c, D30
258hp@4800rpm, 320lbft@3200rpm, 1/4 mile = [email protected], 0-60 = 5.9secs
Websites - Jeep 4.0 Performance, 4.6L Stroker Build-Up, Dino's Jeep Tricks
Dr. Dyno said:That was me
http://jeep4.0performance.4mg.com/ramair.html
Dr. Dyno,
Have you ever seen anyone run the numbers on teh air temperature by creating more space by raising the back of the hood. Before I tried your insulation technique I created a 1/2 inch gap between the hood and body. It really allowed fo rgood airflow and cooled down the engine compartment.
BSD
A 180° thermostat will NOT increase performance and will NOT increase gas mileage. The only thing it will do is allow your engine to run a little cooler, which is not necessarily a good thing. In the case of Dino, who lives in a very hot climate and (more importantly) has made a LARGE number of other modifications to his engine, it is probably worthwhile. In the case of an otherwise-stock engine a 180° thermostat will provide absolutely no benefit whatsoever.
Thanks, guys. I appreciate all the comments. I guess I'll stick with a 195* and possibly do the hood spacers. The only problem there, not to hijack the thread I started, might be that I plan on doing MadXJ's cowl snorkel and if hot air is flowing out of the spaced hood at speed, it'll just get sucked back into the intake, albeit at a lower temperature than the stock hole sees.
Brian Carpenter
NAXJA Forum User
- Location
- Vermont
HOT air?
Could hot air in the engine compartment actually add to the overall engine temp? I relocated my intake higher to beside the master cylinder.. could that be why I regularly run 230 on the trail?
I have already isolated the electric fan so its on allthe time.. i just can't get it to really cool down.
Could hot air in the engine compartment actually add to the overall engine temp? I relocated my intake higher to beside the master cylinder.. could that be why I regularly run 230 on the trail?
I have already isolated the electric fan so its on allthe time.. i just can't get it to really cool down.
8Mud
NAXJA Forum User
- Location
- Central Germany
Re: HOT air?
The manifold temp. sensor (MAT), is gonna affect fuel to air ratio, with the intake air hot. One of the reasons they put intake in front behind the headlights was to get air as cool as possible.
Eagle is the radiator Guru, tipped me off to look in the bottom of my radiator for built up deposits (used a dental mirror and a flashlight to look in the outlet). They were sure there, way past the point where flush was gonna help much. Like a half pound of near solid deposits. Cut the radiator open out of curiosity, what I found in there was really enlightening, could hardly believe the radiator was working at all.
Fan clutch, has a large affect on low speed cooling, the mechanical fan moves more air than most electric fans do.
Opening the back of the hood, could be a mixed bag, it vents air at low speeds and sucks air at high speeds. Try it, do what I did, tapped some pieces of ribbon near the bottom of the windshield and on the grill by the wipers, went for a drive.
Imagine the amount of the opening in the back of the hood has some influence into how it vents or flows. Might be worthwhile to try different size gaps at the back of the hood.
Don´t do what I did, and cant the hood so much, it wouldn´t open without a whole lot of pressure on the locking mech and cable.
Guys on the modified board say Lebaron hood vents work well.
Venting the hood near the intake for the heater, doesn´t seem like a smart move to me (exhaust manifolds crack often), of course I live in cold country. Heater is pretty darned important and I spend much of the year with the windows rolled up and the heater on full.
Try a little experiment, feel the air coming out behind the wheel on the drivers side with the aux fan on, then with the fan off. Try the passengers side, the same way, just could be me, but the air exiting the drivers side seems noticably hotter. Could just be thats the side with the exhaust manifold.Brian Carpenter said:
The manifold temp. sensor (MAT), is gonna affect fuel to air ratio, with the intake air hot. One of the reasons they put intake in front behind the headlights was to get air as cool as possible.
Eagle is the radiator Guru, tipped me off to look in the bottom of my radiator for built up deposits (used a dental mirror and a flashlight to look in the outlet). They were sure there, way past the point where flush was gonna help much. Like a half pound of near solid deposits. Cut the radiator open out of curiosity, what I found in there was really enlightening, could hardly believe the radiator was working at all.
Fan clutch, has a large affect on low speed cooling, the mechanical fan moves more air than most electric fans do.
Opening the back of the hood, could be a mixed bag, it vents air at low speeds and sucks air at high speeds. Try it, do what I did, tapped some pieces of ribbon near the bottom of the windshield and on the grill by the wipers, went for a drive.
Imagine the amount of the opening in the back of the hood has some influence into how it vents or flows. Might be worthwhile to try different size gaps at the back of the hood.
Don´t do what I did, and cant the hood so much, it wouldn´t open without a whole lot of pressure on the locking mech and cable.
Guys on the modified board say Lebaron hood vents work well.
Venting the hood near the intake for the heater, doesn´t seem like a smart move to me (exhaust manifolds crack often), of course I live in cold country. Heater is pretty darned important and I spend much of the year with the windows rolled up and the heater on full.
Dr. Dyno
NAXJA Forum User
- Location
- Al Ain, UAE
BSD said:Dr. Dyno said:That was me
http://jeep4.0performance.4mg.com/ramair.html
Dr. Dyno,
Have you ever seen anyone run the numbers on the air temperature by creating more space by raising the back of the hood. Before I tried your insulation technique I created a 1/2 inch gap between the hood and body. It really allowed fo rgood airflow and cooled down the engine compartment.
BSD
Not as far as I know. Using spacers to raise the rear of the hood is something of a mixed blessing. At low speed, hot air WILL be vented from under the hood so it's good if you're wheeling or driving in slow traffic. Unfortunately at high speed, outside air will get sucked under the hood in that area because it becomes a negative pressure zone (that's why the heater vents are there). I wouldn't like that to happen if it's raining heavily.
As an alternative, you could just remove the rubber weatherproofing strip that's rivited behind the hood and put it back when it rains.
As far as hood vents go, they are only effective if you place them near the front of the hood. Many people place them near the back and that's no good at all.
Dr. Dyno,
Now you got me curious. I think I will tape some thread along the edge and take for a spin. I am curious if it does result in negative air pressure at high speeds. My thinking would be that the air entering through the grill and radiator as well as from under the Jeep would still keep a positive airflow. I could see the airflow not being as strong as over the hood, but can not see how it owuld be a negative flow. Guess I'll find out. By the way, I liked your site and discussion.
BSD
Now you got me curious. I think I will tape some thread along the edge and take for a spin. I am curious if it does result in negative air pressure at high speeds. My thinking would be that the air entering through the grill and radiator as well as from under the Jeep would still keep a positive airflow. I could see the airflow not being as strong as over the hood, but can not see how it owuld be a negative flow. Guess I'll find out. By the way, I liked your site and discussion.
BSD
