Thermostat opinions - Lower Set point for Summer

[MaximumMini]

Whenever the A/C compressor is running, the fans must be running - on any car that's sitting still.

From what I found online the Caravan uses a pressure transducer not a switch. The PCM gets that input signal, then switches on the fan output speed.
It is possible there is so little charge in the system that it's not signalling that the system is running.
If you have a scan tool you may be able to see what the PCM sees.

I found a video on youtube describing a problem on an '05, which uses the same transducer. It may be worth a watch.

Thank you!
Very informative and helpful post. I'm checking this today.

 

[zrxkawboy]

one has a 3.3L, the other a 3.8L. Both 1999

AFAIK, these engines are not known for head gasket failures. The mfr's approach seems to work fine.

 

[Hohn]

I have found when I installed a cooler thermostat in a vehicle which ran too warm that eventually the temperature crept up to the same temperature as before. It just took longer to get there. If you think your engine is going to run 10-15 degrees cooler, don't count on it. The cooler thermostat was not the long term solution.

I would try to find out why your Dodge is running too warm. My bet is the radiator is not in the greatest shape. The fins on the radiator or condensor are partially blocked , reducing air flow or the fan is not energizing at the proper temperature. I would believe the fan should be turning on sooner than what you mentioned..

This x1000. The cooler thermostat doesn't change the basic heat flow relationship. It just changes the point where you start down the some problematic path.

If your engine is running above thermostat temp, or even noticeably warmer in the summer, you have issues other than the thermostat.

 

[MaximumMini]

AFAIK, these engines are not known for head gasket failures. The mfr's approach seems to work fine.

I own and maintain 3 of these. Just curious, how many do own and maintain?
They're good proven engines, but subject to the same problems if abused.

 

[MaximumMini]

This x1000. The cooler thermostat doesn't change the basic heat flow relationship. It just changes the point where you start down the some problematic path.

If your engine is running above thermostat temp, or even noticeably warmer in the summer, you have issues other than the thermostat.

For many vehicles I would say this is true.
But most people with these minivans report about the same as I posted.
Thermostat temp is 195F
As you can see by design, the fans don't come on until 224F (220F is a misprint, it shows 224F everywhere else in the FSM)

Factory specs for radiator fan operation.....

 

[MaximumMini]

Whenever the A/C compressor is running, the fans must be running - on any car that's sitting still.

From what I found online the Caravan uses a pressure transducer not a switch. The PCM gets that input signal, then switches on the fan output speed.
It is possible there is so little charge in the system that it's not signalling that the system is running.
If you have a scan tool you may be able to see what the PCM sees.

I found a video on youtube describing a problem on an '05, which uses the same transducer. It may be worth a watch.

It seems that there is a delay from the time that the vehicle is started, then after the AC is turned on there is up to a 1 minute delay until the fans come on. I would assume this is due to rise in pressure of the refrigerant after turning the AC on.

According to the video posted, it could also be a faulty connector. I jiggled the connector before starting the engine but no idea if that had any effect. The transducer itself is not much more than a year or so old IIRC.
Checking both and thanks again.

 

[Hohn]

For many vehicles I would say this is true.
But most people with these minivans report about the same as I posted.
Thermostat temp is 195F
As you can see by design, the fans don't come on until 224F (220F is a misprint, it shows 224F everywhere else in the FSM)

Factory specs for radiator fan operation.....
View attachment 287427

Thermostat temp still doesn't matter.

The elevated operating temperature is the equilibrium point between heat entering the system and heat leaving the system. If you want to lower the operating temperature, you have to add less heat to the cooling system or remove more of it from the cooling system.

If your equilibrium temperature is above the thermostat cracking temp, a lower stat temp can do nothing for you. A cooler thermostat can only lower the *minimum* running temp, not the max!

In other words, a lower thermostat can only lower temps when there is excess cooling capacity available. But if this was true, you would never see temps above 195 on your current thermostat.

The fans coming on means your basic heat exchange rate is saturated but the temperature is still rising. Hence, a cooler stat can do nothing to lower peak temps in hot weather. The best it can do it take a bit longer to get to the higher temp. But peak temps will still be the same.


If you are worried about the running temp, improving heat transfer efficiency is the best bet. Make sure your radiator isn't plugged full of bugs or mangled with bent fins. Consider a cooling system flush. Finally, if you live in a warm climate, consider a lower mix ratio of coolant. Instead of 50/50, try 60% water or 65% water. Water is much more effective at heat transfer than glycol is.

 

[AdmiralYoda]

Seriously...your best option is to have a tuner set the Fan-On temp to something like 200F and Fan-Off temp to 190F. It will cost a lot less than you think and can even be done through the mail. They will send you an OBDII-to-USB cable that will connect to a laptop and it will take all of 5 minutes.

Although it is a minivan there are tons of Dodge/Jeep/Chrysler people of that vintage getting tunes. Mostly Magnum V8's but the software is the same.

 

[CarlB]

If the goal is to be cooler, then you need to increase capacity (more coolant) and/or increase convection (more CFM of air).

 

[BigCahuna]

I'm surprised nobody mentioned draining, and flushing out the cooling system. If your radiator is partially plugged up, it can't possibly cool like it was designed to. I'd try flushing the bejeebers out of it, then installing the correct thermostat that it came with from the factory. I'd only consider changing the thermostat to a lower temp, if I was using the car in a part of he country where the temp is over 100 degrees most of the time.,,

 

[chorty]

Also, mind you, the PCM software has certain expectations.

I did a thermostat on my old 98 1500 Silverado and drilled a few 1/16" holes as well.

Worked awesome in the summer. When it came January...

Well, backfire. When its below freezing outside, unless I keep plastic over the radiator, I can't get enough block heat to satisfy the PCM/TCM, and the torque converter won't lock up..,..not to mention the defrost for the windshield isn't at all impressive.


On the Chevy tracker yard vehicle, in did the same thing. Between modifying the clutch fan into a roaring hurricane Katrina, and thermostat extra drilled holes, when I pull the cardboard off the radiator, as the temps drop, the RPMs slowly creep back up as if it was back to an overnight cold start. Again, PCM is getting confused. The temp sender is accurate, but the software is expecting a certain range. And that thermostat is expected to hold it somewhere reasonable for its programmed parameters.

Don't get too creative. You'll be taking a step backwards. Go OEM and be done with it.

 

[chorty]

I'm surprised nobody mentioned draining, and flushing out the cooling system. If your radiator is partially plugged up, it can't possibly cool like it was designed to. I'd try flushing the bejeebers out of it, then installing the correct thermostat that it came with from the factory. I'd only consider changing the thermostat to a lower temp, if I was using the car in a part of he country where the temp is over 100 degrees most of the time.,,

Correct. Good advice.

OP needs to make sure his heat shedding radiator is actually shedding heat.

I modified my 2001 tracker with a heavily hole drilled thermostat and roaring fan. Why?

I've been doing yard clean up. When its 95*F and I'm pulling 75-100 car tires on a tow strap in low range, TRYING to break CV shafts and ujoints,, at the high speed of 3 MPH, need to shed heat.

That little 2.0 and torque converter can make some serious BTUs....quickly

 

[zrxkawboy]

I own and maintain 3 of these. Just curious, how many do own and maintain?
They're good proven engines, but subject to the same problems if abused.

I only had 1 with the 3.8. Sold it with over 170k miles, still running very well.

I agree that any engine can fail if abused. I just don't believe that it is abuse to allow a vehicle to run the way the engineers designed it.

 

[mk378]

Part of the design is 50% glycol coolant. That is necessary to keep the boiling point up.

 

[MaximumMini]

I'm surprised nobody mentioned draining, and flushing out the cooling system. If your radiator is partially plugged up, it can't possibly cool like it was designed to. I'd try flushing the bejeebers out of it, then installing the correct thermostat that it came with from the factory. I'd only consider changing the thermostat to a lower temp, if I was using the car in a part of he country where the temp is over 100 degrees most of the time.,,

It probably wasn't mentioned because I think somewhere I mentioned the radiator is only a year old and has been drained, cleaned and flushed at least twice in the last 12 months? Maybe another post. My coolant is crystal clear clean. When I drain it into a bucket I could read the year off a penny at the bottom.

After all of this....I have to say the radiator for these minivans of this year especially (because of the restrictive to flow front fascia design), the small radiator (1 row, 1 inch thick) and that it incorporates a transmission cooler in the end caps and has an oil cooler stuck on front is probably just too much for those particularly hot summer days sitting in bumper to bumper traffic at 105F ambient.

 

[MaximumMini]

Part of the design is 50% glycol coolant. That is necessary to keep the boiling point up.

I only use about 15/85 antifreeze/water since it never gets cold here.
Antifreeze probably helps a little but.....
IIRC, isn't it the coolant system pressure that makes the most difference in coolant boiling point?
That's why if you open the coolant cap with the coolant hot it will still erupt in a gushing volcano of boiling hot water/antifreeze.
It boils instantly when the pressure is released. I've never really seen antifreeze prevent that personally.

 

[MaximumMini]

I only had 1 with the 3.8. Sold it with over 170k miles, still running very well.

I agree that any engine can fail if abused. I just don't believe that it is abuse to allow a vehicle to run the way the engineers designed it.

Fair enough.
But improving on the design is a good thing, no?

When I sit long enough, the temps will keep creeping up until it hits 230F when the fans kick on high.
I found out today that the radiators fans do come on anytime the AC is on with the caveat that it only comes on with AC on when the refrigerant pressure transducer voltage reaches at least .451v
That takes about 1 minute from a cold first start for the day.

But even with those fans on, given sitting long enough, it will eventually reach 230F on days hovering near or above 100F ambient.
Like others said, if it's as clean as it can get now, and everything else is right, then there's probably a heat rejection capacity issue with the design for very hot days.

Maybe if I moved the transmission cooler away from the radiator and to a separate cooler that would help.
That poor radiator has a lot of demands on it.
Maybe going to a 2 row (rather than the OEM 1 row) radiator?
What about a thermostat with a larger opening than OEM to allow more volume of water to pass the thermostat housing per minute:?
Motorad has those. 50% more flow through the thermostat than conventional thermostats. (assuming there is at least some flow restriction now)

 

[SumGuy]

What engine are we talking about here?

On my several Chrysler 300m's (model years 2000 through 2004) with 3.5L V6, I changed the thermostat from 180 to 170. The T-stats on this engine is actually located on the INFLOW side of the block. It senses coolant flowing past it within the block and opens up when the temp exceeds 180F. In order to find a suitable (correct physical size) 170 T-stat on RockAuto, I had to set my search criteria for a 1995 Subaru Justi.

I've also rigged a manual switch in the cabin to turn on the radiator fans, which I find do not automatically turn on at any rational temperature. I've wired the switch directly to the fan relay terminals so that the ECU can turn the fans on if it feels like it, but I find that it never does.

 

[ripcord]

Fair enough.
But improving on the design is a good thing, no?

When I sit long enough, the temps will keep creeping up until it hits 230F when the fans kick on high.
I found out today that the radiators fans do come on anytime the AC is on with the caveat that it only comes on with AC on when the refrigerant pressure transducer voltage reaches at least .451v
That takes about 1 minute from a cold first start for the day.

But even with those fans on, given sitting long enough, it will eventually reach 230F on days hovering near or above 100F ambient.
Like others said, if it's as clean as it can get now, and everything else is right, then there's probably a heat rejection capacity issue with the design for very hot days.

Maybe if I moved the transmission cooler away from the radiator and to a separate cooler that would help.
That poor radiator has a lot of demands on it.
Maybe going to a 2 row (rather than the OEM 1 row) radiator?
What about a thermostat with a larger opening than OEM to allow more volume of water to pass the thermostat housing per minute:?
Motorad has those. 50% more flow through the thermostat than conventional thermostats. (assuming there is at least some flow restriction now)

A faster flowing thermostat won't help if the fans can't cool the coolant leaving the radiator significantly below the engine temp. Do you have a infrared thermometer gun? It might be instructive to compare the radiator inlet temp vs the outlet with the fans running. Also, have you verified the actual engine temps or are you only going by what the ECU reports?

 

[MaximumMini]

A faster flowing thermostat won't help if the fans can't cool the coolant leaving the radiator significantly below the engine temp. Do you have a infrared thermometer gun? It might be instructive to compare the radiator inlet temp vs the outlet with the fans running. Also, have you verified the actual engine temps or are you only going by what the ECU reports?

Yes. Good idea.
I'm going by what the ECU reports. The temp sensor is new. I made an assumption that the temp would be accurate.
No other way I know of to get a precise coolant temp when hot without adding something.
Laser thermometer should be close.