As I'm sure many of the people here with the Duratec 2.3L engine know, the cooling system leaves a lot to be desired. I've been fighting a mostly-losing battle with mine, so I'm just about ready to turn the tides on it. After losing the radiator (plastic side tanks only; aluminum core is fine), coolant bottle, and finally the bypass pipe (yes, the one that wraps around the engine), I'm ready to start overstepping the OEM solution a bit for something a little less terrible.

The current modification I'm running is a 2006 mechanical thermostat in place of the original electronic unit. It was over $100 cheaper, and it works beautifully. The engine gets up to temperature really fast and never even comes close to overheating afterward. I've never seen it behave that well. Unfortunately, it's missing the electrical connection. Thus, whenever the engine starts up, the computer freaks out and throws a CEL for the missing thermostat circuit. Of course, this further proves why it's useless since I can hook up a scan tool and clear it immediately. It will not come back on until the next start-up. This is a problem since I'm due for inspection next month. This code isn't emissions-related at all, so I don't know if it'll affect anything. But still, I'd rather not find out at the last minute and have to scramble together a fix then. This is the year that Texas is combining the inspection and registration stickers, so it'll create a headache of unparalleled magnitude if I'm late on it.

Ideally, I'd just plug the old thermostat in there and leave it hanging on the side, but the entire thing just kinda fell apart after I changed it. Gotta love plastic, right? Anyone know the details of how that circuit works so I can make something to fake a connection? I have lots of wiring diagrams, but I don't really understand what it's doing.

__________________
2003 Ford Ranger XLT
2.3L I4 Duratec DOHC, 5R44E 5-speed auto, RWD, 7.5" Open w/ 4.10 Ratio, Gibson split-rear catback
Sonic Blue Pearl with dark gray trim

Hello,

It sounds like you are replacing the analog coolent temperature sensor not a thermostat switch. This fix shouldn't matter as long as the cable only has two wires.

What you will need is a 5k linear taper potentiometer. Here is a link for amazon http://amzn.to/1OQ3tLb and another for RadioShack http://www.radioshack.com/5k-ohm-lin...s/2711714.html

All you have to do is join the left and center legs, this will become one of the connections to the wire harness, the right leg will become the other connection to the harness. Using a multemeter, set to Ohms, turn the dial all the way counter clockwise. It should read close to 5k ohm. This should equate to roughly 32°F to your car. Go ahead and connect it to your car and turn the keys to the on position. Slowly turn the dial clockwise and the temp gauge should start rising. When it gets to normal running temp, tape everything off and secure the assembly so it does not rattle around.

The part you need to watch out for is that the computer mixes the fuel/air ratio differently at different temperatures. With this mod, it may have a hard time running in Winter.

Interesting approach. I actually double-checked my wiring diagrams, and it shows that the electronic thermostat is PCM-controlled to allow the computer to adjust the coolant temperature whenever it needs to. However, it lists the component itself as a potentiometer. It looks like pin 1 is a signal from the PCM, and pin 2 is a straight line from fuse 1.41 (hot in start/run). That same fuse powers a lot of other sensors and stuff (O2 sensors, EGR stuff, etc.). The PCM signal seems to be positive power. But as far as I know, one of the main reasons Ford stopped using the electronic thermostat here is because the computer never actually had to use it for anything. Mechanical does the job just fine, and computer-control doesn't seem to improve or even change anything.

I was going to just try taking an old load resistor that shipped with LED turn signals and bridging the two pins with it. The entire purpose of that thing is to suck up extra power to make the flasher relay think there's something else there, so maybe the same trick would work on this? My only concern is that both pins look to be supplying positive power, and there is no obvious grounding point on anything. Unless, perhaps, it was grounding to one of metal spacers for the thermostat housing screws? That would screw directly into the block, potentially supplying ground from that. But I don't know.

Also, there is another coolant temperature sensor in this system, so I don't think that's the circuit we're looking at here. I thought it was a heater that was designed to force the thermostat open when energized.

__________________
2003 Ford Ranger XLT
2.3L I4 Duratec DOHC, 5R44E 5-speed auto, RWD, 7.5" Open w/ 4.10 Ratio, Gibson split-rear catback
Sonic Blue Pearl with dark gray trim

Well, it took long enough to get to it, but I've finally addressed this issue. The leaking pipe has been replaced, and it looks like the system is retaining all coolant. Good start. The CEL for the stupid thermostat was still around though, so here's my (hopeful) fix:



I cleared the CEL and ran the engine a bit after tossing that in. No light yet. I'll run it through a nice heat cycle tonight though, so we'll see if it actually works.

__________________
2003 Ford Ranger XLT
2.3L I4 Duratec DOHC, 5R44E 5-speed auto, RWD, 7.5" Open w/ 4.10 Ratio, Gibson split-rear catback
Sonic Blue Pearl with dark gray trim

As I will be changing the thermostat and all that fairly soon, id be fairly curious to find out details about what youve done. Id love to shitcan the electric thermocrap they used on the 01-03 when I do mine. I could pin out the thermostat and prolly figure it out on my own, but if it works for you, let us know please

__________________
2002 Ford Ranger XLT Supercab, 2.3L Duratec I4, 5-speed manual, 4.10 gears, ~100,000 miles
Power nothing with air conditioning; crank windows for life!
Throttle cable mod, retained accessory power mod, 2006 thermostat w/resistor mod
Headlight relay harness, Philips xtreme-vision bulbs
P235/75R15 Michelin LTX M/S2s

Welp, after living with it for a few days, I think I can call this workaround a success. I haven't seen a check engine light at all since installation, and it passed inspection with no issues. Anyone looking to modify the thermostat in their '01–'03 2.3L Ranger, this seems to work. Just buy a newer thermostat assembly (the Motorcraft unit without a heater circuit. I got it by looking at parts for an '06 2.3L), and then tack a resistor between the wires in the connector. Just keep in mind that one of those wires is 12V, so be prepared for that resistor to get a little warm. I mounted it to that metal bracket for a reason.

__________________
2003 Ford Ranger XLT
2.3L I4 Duratec DOHC, 5R44E 5-speed auto, RWD, 7.5" Open w/ 4.10 Ratio, Gibson split-rear catback
Sonic Blue Pearl with dark gray trim

I just changed the degas bottle on mine yesterday (I started getting cracks at the cap like you did) and the thermostat and coolant recovery hose/tee are the only cooling components left to change. Already done the radiator, water pump, heater control valve, and cap.

After living with it a few days, does it behave any different than before? What value resistor did you use out of curiosity? Did you determine what value to get by ohming out the heater circuit on your old one or just took a guess?

**EDIT** Also, when I look on Rock Auto at thermostats (for an 06 or an 02), I see mentions of 208 degrees and 190 degrees. Do you happen to know the temperature the thermostat should be? I dont even see that info in my manual for the truck.

__________________
2002 Ford Ranger XLT Supercab, 2.3L Duratec I4, 5-speed manual, 4.10 gears, ~100,000 miles
Power nothing with air conditioning; crank windows for life!
Throttle cable mod, retained accessory power mod, 2006 thermostat w/resistor mod
Headlight relay harness, Philips xtreme-vision bulbs
P235/75R15 Michelin LTX M/S2s

Get the Motorcraft thermostat. The rest aren't worth it. 190F is the one you want, and Motorcraft is typically the only one I see that meets it. The rest are either 180F or 208F. Neither of those are acceptable.

Behavior isn't different at all. I theorized a long time ago that the computer wasn't doing anything with the thermostat after seeing it, and it looks like that's true. From what I've seen over time, this particular engine has an extremely difficult time warming up. The thermostat in any engine is a very critical component for getting it up to temperature, but it looks to be even more extreme for this one. So naturally, it makes perfect sense to put a heater circuit on the thermostat to force it open sooner and make it harder for the engine to warm up at all, right? Good job, Fordzda engineers. That was a very smart decision.

I just used an old LED turn signal resistor. I have a few of those lying around from my LED experimentation days, so there was plenty to work with. Since I installed an electronic flasher relay, those resistors are completely worthless to me. Only reason I kept them was because I thought they might come in handy one day. Hooray!

Oh, and if you're looking to replace the recovery hose, here's the secret to doing it right: jack up the front end, then remove both front tires, inner fenders, and the catalytic converters. That will give you the space you need to wiggle the assembly in and out without having to remove the transmission or exhaust manifold. Took me a few hours of trial and error to nail that.

__________________
2003 Ford Ranger XLT
2.3L I4 Duratec DOHC, 5R44E 5-speed auto, RWD, 7.5" Open w/ 4.10 Ratio, Gibson split-rear catback
Sonic Blue Pearl with dark gray trim

Good deal- thanks for the info. I'm prolly gonna do the thermostat after Christmas so I'll bump this thread then. I'll prolly just ohm the heater element out and try to find a resistor with a heatsink on it (since I have none lying around).

As for the coolant hose, ill keep your trick in mind. Fortunately/unfortunately I'm going to be pulling my trans anyways to change the clutch slave, so might as well knock it out then..

__________________
2002 Ford Ranger XLT Supercab, 2.3L Duratec I4, 5-speed manual, 4.10 gears, ~100,000 miles
Power nothing with air conditioning; crank windows for life!
Throttle cable mod, retained accessory power mod, 2006 thermostat w/resistor mod
Headlight relay harness, Philips xtreme-vision bulbs
P235/75R15 Michelin LTX M/S2s

I have done a bunch of research on the thermostat since you made this post and I believe it works differently than we thought prior.

A press release for the duratecs introduction mentions:
and further Ive read:
Converting to Fahrenheit, that means the bulb-wax aspect of the thermostat starts to open at 208 degrees and becomes fully open at 235.4 deg F! When cruising, it doesnt apply power to the heater circuit, and allows coolant temperature to ease up to 208+ degrees. The only way this thermostat can actually regulate at 190 degrees F is if you have your foot in the floor, where it tries to bring the temp down to 190 for the purpose of more timing advance.

The biggest issue with this is that it works in theory but not in practice. You are cruising 55 on a 2 lane and go to make a right. The temperature has crept up to 220+ deg F as the pcm has removed power from the heater circuit, so when you go to apply throttle to power away from the right turn, the truck is a dog because it has to keep the timing retarded to avoid knock until the thermostat/pcm brings the temps down. It may happen quickly, but not without delay.

Also, its hell on the cooling system. The system is constantly fluctuating between 190-220+ depending on load conditions. Not only is the constant pressure difference hard on the plastics in this system, but the higher pressures cause more pressure (approaching the 16psi cap limit) on the entire cooling system (water pump seal, radiator tanks, degas bottle, etc).

Some of us dealing with coolant loss also might be a victim of this thermostat. Heres a post I found:
As my truck has never boiled over (where it pours out of the bottle and overheats, etc), but has nonetheless shown spots on the coolant bottle, I think this might have been the case with me. I have done every conceivable head gasket test and theyve all passed, so heres hoping..

I completed the mod you did here tonight. 2006 thermostat with a 1500 ohm 1/2 watt resistor from radio shack. I have instantly noticed cylinder head temps about 20 degrees Fahrenheit cooler and have no check engine light. Im hopeful this might kill my very slow coolant loss issue as well as kill my pinging issue on another thread.

**EDIT** Either way, this thermostat was shittastic no doubt about it.

__________________
2002 Ford Ranger XLT Supercab, 2.3L Duratec I4, 5-speed manual, 4.10 gears, ~100,000 miles
Power nothing with air conditioning; crank windows for life!
Throttle cable mod, retained accessory power mod, 2006 thermostat w/resistor mod
Headlight relay harness, Philips xtreme-vision bulbs
P235/75R15 Michelin LTX M/S2s

Maybe adding a resistor to the circuit instead of bypassing it would work better. Seems running at 208F is too close to 212F, and too close to 'overheating' where the timing gets clobbered. If you were to add a fixed resistor that biased the temperature reading in a +10F or so range, the thing would still keep the temperature up, but not so close to overheating.
It really is a decent idea, but they took it too close to the edge. I'd dial it back if I had one of them. Just need to diddle with the ohmage so the computer is fooled into thinking it is 10F hotter than it is, giving a bit of design margin.
Does that sound reasonable?
tom

I dont think this would work, mainly because the heater circuit is the only way to make the thermostat function cooler- allow me to clarify. The best I can tell, the setup has a cylinder head temperature sensor and a coolant temperature sender. The cylinder head temperature sensor is used to determine fueling and timing, while the coolant temperature sender is used to control the temp gauge on the cluster.

Interestingly, the coolant sender doesnt interface with the gauge directly- it goes to the PCM as an input, and the PCM uses its info against stored algorithms to determine if the engine is "hot." For example, if youre FWOT and it should read 190 degrees at the coolant temperature sender but it actually reads 225, the PCM sends the temp gauge up from mid-gauge towards hot. However, if cruising steady-state at 55, 225 at the coolant temp sender indicates no issue and thus the gauge stays mid-gauge. I believe they did this- similar to the dummy oil pressure gauge- to avoid service complaints where people see the temperature wildly fluctuating and assume something is wrong.

This is all to say, the thermostat itself doesnt report anything to the PCM. Its electrical connector is entirely for the heater circuit where the PCM tries to influence engine temperature, but nonetheless the PCM determines fuel and timing maps based on values reported by the cylinder head temperature sensor.

If you put in a resistor to weaken the effect of the heater circuit, I fear it would cause it to run hotter as the heater circuit could no longer open the thermostat as much or as fast. Also, in steady-state cruise conditions where the heater circuit has no power applied, the resistor would have no effect and the temps would still creep 220+. I have not hooked in a voltmeter to test while driving, so I cannot say for sure.

I agree with you about it being a good idea they took too far. I think they realized this and thats why they changed it to a fixed thermostat 2004+. When you look at the tiny amount of air in the degas bottle relative to the coolant system's capacity and consider all the expansion that takes place, it seems inevitable the cooling system pressure would exceed 16psi when the system runs the coolant temps up to 220+ causing venting at the cap not to mention all the additional stress.

__________________
2002 Ford Ranger XLT Supercab, 2.3L Duratec I4, 5-speed manual, 4.10 gears, ~100,000 miles
Power nothing with air conditioning; crank windows for life!
Throttle cable mod, retained accessory power mod, 2006 thermostat w/resistor mod
Headlight relay harness, Philips xtreme-vision bulbs
P235/75R15 Michelin LTX M/S2s

I think I get it... but have to ponder more ... maybe.

I think the volume of the water jackets or actually coolant jackets around the cylinders is smaller than in the past, so there's less coolant to heat up before getting to operating temp, thus less volume expanding from cold to 200+, thus less need for a larger degas.
If you heat 10 quarts, you get 10.x if you heat 5, you get 5.y ... y being 1/2 of x. sort of.
If you think about it, the only reason for coolant is to remove excess heat and prevent a meltdown or seizing. If you have too much volume, you waste energy heating that as all it does is mingle around in the 'jacket'. Gets hot, mixes or stays, or gets flowed to the radiator. Why so much? I dunno, except for 'swings' in heat output, giving a 'buffer' of 'heatable' coolant to absorb peaks of heat, that is then mixed with the other coolant, more just hanging around in the system, and taking more energy before the whole mix rises 1degree F. or 20.
Less volume makes the system significantly less able to handle peaks of heat output, such as with a turbo, etc. To handle that you need a quick-acting thermostat that can bang-bang go wide open in an instant to allow that wonderful cooling juice to flow over the hot spots near the exhaust valves... etc.
Maybe they missed on the design, but the less coolant you have in the system the quicker it will heat up and thus use less fuel... plus it weighs less ... PLUS the worst time for emission control is immediately after start-up, so if they can get it hot NOW, and get the O2 working for 'closed loop', it is better than taking more time.
Mebbe I shoulda been an engineer. Or not.
tom

All good thoughts/info. I think the capacity is about right- the truck warms up pretty quick once it gets a load.

**VERY LATE EDIT** I cant believe I missed this other thread that gives more details about this thermostat:
Over heating and gage shows Normal?

Since this thread has some great info on the thermostat function, Ill add some key points here to consolidate information:
My theory is that the PCM is programmed too "weakly" in terms of cooling the engine down with the thermostat, and in certain circumstances it can cause the pressures in the system to exceed 16psi. Since I have changed to the 2006 thermostat, I havent had the cap vent once.

__________________
2002 Ford Ranger XLT Supercab, 2.3L Duratec I4, 5-speed manual, 4.10 gears, ~100,000 miles
Power nothing with air conditioning; crank windows for life!
Throttle cable mod, retained accessory power mod, 2006 thermostat w/resistor mod
Headlight relay harness, Philips xtreme-vision bulbs
P235/75R15 Michelin LTX M/S2s

This is all some pretty interesting information. GSF, do you still have the original electronic thermostat available for any testing? I'm curious to know what else we might be able to learn about the old Duratec cooling setup since it seemed to be the Bane of that particular engine. Although, in all honesty, there were a fair share of Batman villains in that motor, not just Bane. I'd say intake runner valves were the Riddler, but I digress.

Anyway, I find it increasingly curious that Ford opted to switch to so many plastic components in a cooling system that was specifically designed to run through more intense heat cycles than normal. This explains a lot about the part failures that so many of us have had. And also why I don't see many people with newer Rangers running into them.

On a related note, when I bought an SCT tuner last year, MorePowerTuning (the company I bought it through) had a really hard time with my engine. The data they had on their end was inconsistent, so they needed me to log a few test runs in specific conditions to make sure they were looking at the right info. This worries me since they are an extremely specialized tuning company with a lot more information on all of these Ford vehicles than anybody on this forum, or possibly even specialized tuning sites. Combine that with the data log I sent there, and the end result is even more puzzling. I can't use that tune at all. It seemed to just cripple my engine's power every time I hit the gas, which I later discovered was due to ridiculously late spark advance. Seriously, it would jump deeply negative every time I took off, which is exactly the opposite of where it should be going. This new info on the thermostat makes me think that the PCM is counting on that system a lot more than it should be for calculating this stuff. Do you have any sources on the info you were able to gather? I'd like to bundle it up and send it off to MPT to see if they know anything.

__________________
2003 Ford Ranger XLT
2.3L I4 Duratec DOHC, 5R44E 5-speed auto, RWD, 7.5" Open w/ 4.10 Ratio, Gibson split-rear catback
Sonic Blue Pearl with dark gray trim