JT4x4
The Mud Pit => Wrenching => Topic started by: Axle on December 26, 2007, 08:45:41 PM
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Question. If I put a lower temp thermostat in my TJ, do I have to change anything else and will it actually keep my engine cooler?
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Not necessarily. It's not as simple as just lowering the temp at which the thermostat opens. In a cooler region, or during winter, it will usually lower the operating temp of your engine. However durring warmer periods, or when your engine is working harder, it could acutally cause your engine operating temp to rise. "How can that be possible?" I'm glad you asked :)
Heat Transfer is is nothing more than transfering waste heat from the source (your engine) to a heat sink (the air around). For heat transfer to occur, there has to be a temperature difference between the source and the sink. Also, the greater the temp difference between the sink and source, the greater the heat transfer rate. ie: A glass of water at 200 deg in a room that is 70 deg will take less time to cool to 150 deg than it will to cool to 100 degrees (assume the room stays at 70 deg). This is an exponential function.
Now, lets apply that to your engine. We'll start out w/ your engine (source) at 70 deg (summer morning, all parts/fluids are at equal temp) and you are using an 180 deg thermostat. You start up your engine. Immediatly the water in the cylinder jackets and heads starts to warm up untill the water at the thermostat reaches 180 degrees (we'll assume for simplicity's sake that all water is uniform in temp). The water in your radiator is still at a cool 70 deg. The hot and cold water quickly exchange places due to the water pump untill the water at the thermostat is at some temp less than 180 (we'll use 170. A thermostat opens at one temp, and closes at another, slightly lower, temp). The 70 deg water is then heated as the 180 degree water is cooled in the radiator. (Side note: heat transfer from fluid to air (via radiator) is a much less efficient process than from the engine block/heads to the water.) This process continues untill you shut off the engine. Assuming that the outside temp stays the same, and the air flow (cfm) across the radiator is the same during the time the engine is running, a certine amount of heat is transfered from the engine to the air over time (BTU/hr).
Now, lets assume the ony thing changed between the above and this run is the thermostat. The air is still 70 deg, the airflow over the radiator is the same, the engien is under the same load conditions w/ the same efficiency. You now put in a 160 degree thermostat (which closes at 150). The cycle above will still occur, however it will occur more frequently. Once you are in the cycle, w/ water exchanging at 160 vice 180, more heat is being transfered (at least initially) to the water. Good, right? Well, hang on and see what happens. This now cooler (than the pervious example) water enters the radiator. Since it is at a lower temp, the rate of heat transfer (BTU/hr) is a bit lower. Howver, the heat transfer rate to the water in the engine is higher. The water stays a shorter time in the block to heat to the same temp. The water is then staying in the radiator a shorter amount of time, and is not cooling as much (total amount of BTU tranfered to the air is less) as before. Now when this batch of water enters the engine, its hotter than initially. It is much closer to the 160 than it was before. Now even less time is spent in the block to absorb the heat. Eventually this will lead to water remaining above 160 deg, and constantly cycling through the engine and radiator. At about 250 deg, the radiator cap will lift and you will have a boil over (assuming a 15 psi cap).
If your radiator is efficient enough (big enough, larger capacity fans, etc), this may not happen, and your engine will operte just fine. But if you cooling system was designed for a 180 deg thermostat, you will want to consider its heat removal capacity before changing your thermostat to a lower temp. Here in New England, you may be able to get away w/ the change, but if you move to a hotter climate, probably not.
Just my $0.02
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if you want your engine to run cooler, buy an electric fan, with a electronic adjustable thermostat
just my 2 cents. :)
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if you want your engine to run cooler, buy an electric fan, with a electronic adjustable thermostat
just my 2 cents. :)
Thats the first place to start, then go for a better radiator. You can also try some additives (never tried thoes myself).
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Changing the thermostat can mess with the computer.
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Hell, why change it? Take it out. So it takes you engine longer to warm up, you'll get more flow which in the summer when you're wheeling at slow speds with little airflow the Tstat pretty much stays open.
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Hell, why change it? Take it out. So it takes you engine longer to warm up, you'll get more flow which in the summer when you're wheeling at slow speds with little airflow the Tstat pretty much stays open.
then it will overheat on long trips. the thermo closing allows the radiator to work.
you could get a bigger/better radiator if it is a problem, otherwise if it needs replacing just replace it. check your fan clutch too if it is getting warm, I had a fan clutch on an old ford of mine, didn't like it so I took the clutch out and the fan spun all the time, kept the engine cooler and i didn't notice the drop in hp.
honestly if you have the money an eletric fan is the way to go, I'll be getting one later.
ok, so now you know what i think...
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I agree with Doball... it's not that big of deal for you to NOT run a Thermostat. I've ran trucks without them for well over a LONG FRIGGIN TIME with no issues. I put one in the jeep just for good measure and now it's bitting me in the ass. FYI
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Thanks guys. I have a 16" 2500 cfm fan on order. I was thinking about the thermostat because it would be cheaper, but the fan should be all I need. I do still need to replace the fan clutch, though. That will be next. I'm planning on running both fans. If I can fit the electric between the radiator and the engine fan, then I will, so I'll have two pullers. Otherwise, I'll have a pusher and a puller, no biggie. And thanks for the nuke explanation on heat exchange, Rocket! ;)
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http://store.summitracing.com/partdetail.asp?autofilter=1&part=FLX%2D485&N=700+115&autoview=sku (http://store.summitracing.com/partdetail.asp?autofilter=1&part=FLX%2D485&N=700+115&autoview=sku)
that's the fan that I run (after quite a bit of research on them) and I absolutely love it!
but with that one, there's no way you could run 2 fans (not like I understand why you'd want to)
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I run a taurus fan on my rubi
love the quicker warmups never have needed to wire up high speed side.
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electric is the best way. but, it could be a simple case of mud tightly packed into the radiator.
that was my problem. cruising down the highway @ 75 heat on high, dying with all the windows down and the truck almost over heated twice.
sprayed out the rad for 2 hours and it was good as new. although, my in-laws drive way was absolutely covered in mud.
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It hasn't been overheating. I just want to squeeze out a few extra horses and get an extra mpg or two.
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It hasn't been overheating. I just want to squeeze out a few extra hoses and get an extra mpg or two.
hold on cow boy.
no hose squeezeing on this forum.
dont ask. and please dont tell
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start with an electric fan I can show ya how I did mine if ya want, using a junkyard fan you should be able to spen less than $120 if you want and I gained almost a full mile to the gallon on the freeway
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Thanks guys. I have a 16" 2500 cfm fan on order. I was thinking about the thermostat because it would be cheaper, but the fan should be all I need. I do still need to replace the fan clutch, though. That will be next. I'm planning on running both fans. If I can fit the electric between the radiator and the engine fan, then I will, so I'll have two pullers. Otherwise, I'll have a pusher and a puller, no biggie. And thanks for the nuke explanation on heat exchange, Rocket! ;)
no prob. Glad my education has some use ;D
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It hasn't been overheating. I just want to squeeze out a few extra hoses and get an extra mpg or two.
hold on cow boy.
no hose squeezeing on this forum.
dont ask. and please dont tell
Jon, you are a flippin' comedian!!!! Cowboy... he he he.... I'm dying here
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thanks.
;D
i try,
but it was open for comment.
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It hasn't been overheating. I just want to squeeze out a few extra horses and get an extra mpg or two.
How exactly is that?
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x2 ?
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x3
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X4
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Well, if the engine runs a little cooler, then it should give me those two things. Right? Anyway, I got my fan today, so I'm about to start (1330) putting it in. If anyone is bored, come on over as I wouldn't turn any help away. I live right down the road from Doball. 5 Hart St.
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imo, you'll gain the most (hp and mpg) by taking off your clutch fan completely, just by reducing the load on the engine
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Well, all finished. And it only took me 4 hours! ::)
Thanks for the advice, Al. That's a project for another day. I had to mount it as a pusher, so when I'm ready to get rid of the regular fan, all I have to do is switch the blade, and remount it on the other side. I'll try it like this for a while, and see how it goes.
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glad it came out good
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it does look good. I'm proballt going to end up with one soon.
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yeah me too. something to help suck all the mud out of the radiator
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a puller is probably better than a pusher if you love the mud; the radiator can act as a sheild so you dont' burry your (expensive) electrical fan in the water and short it out!
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a decent electric fan won't short out under water, but one thing I have heard is that a lot of people who really like mud and water will wire in a manual OFF override switch, and turn it off for water crossings. Apparently, it's possible for the extra resistance of the water or mud to pull the fan blades into the radiator, and break either the fan or the radiator or both.
I haven't had any problems with mine.
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I wired an off switch just in case.
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good plan.
i have heard the whole fan in the radiator thing when wheeling. usually due to hitting something though.
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I decided to run this one like the one I had on the cj-7. It's only a 12.5 amp draw, so I used a manual on/off 30amp switch with a 25 amp inline fuse. That way, if there is a short, the inline fuse will bust before I get zapped at the switch. A thermostat relay was more than I was willing to spend right now. I might throw one in later, especially if I take out the belt driven fan and go straight electric.
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ok so you just put an additional fan on and didn't take the clutch one off. To gain the most mpg, Al is right you need to take it off and put just an electic. A friend of mine did that with his Tahoe and picked up 2 mpg just from that. And as far as the taking the Thermostate out, it won't cause you to over heat, but it can cause no heat in the winter. My thermostat was stuck open on my old 73 torino back in 2005 and I drove here to Washington DC with no heat because of the thermostat. It would get hot at low speed or just sitting there for like ever, but one I was going over 35 I lost the heat. Once I changed the thermostat, It worked again. So the lower temp thermostat and the electric fan is the best more for hp and mpg.