Thermostat opinions - Lower Set point for Summer

[MaximumMini]

Just because your body does not want to be 224F does not mean your engine does not like it. 224 is perfectly acceptable for it.

True, but since the fans are designed to come ON at that temp, then it seems the factory agrees with my perception?
Ideally, I would like to see the temps stay below 215F at ALL times. I have seen it reach 228F a few times. That's getting uncomfortable close to 260F IMO, where head gasket damage becomes likely.

At 228F, if anything went wrong in the cooling system, like a hose developed a leak, which would lower system pressure instantly, the temp "could" shoot up to 260 or more very quickly. I want a better margin of "safety"?

Stinkin thinkin?

 

[mk378]

When sitting still, any car will heat up until the fans come on. If you want to modify something, it has to be the fan logic. The thermostat has nothing to do with this.

The smart way to control radiator fans is to measure the temperature of the coolant leaving the radiator. When it rises to about 160 that means that the radiator isn't actually dissipating heat, likely because of a lack of air flow. So the fans come on. Many cars have this system but it does require an additional sensor compared to using engine temperature which is already being measured.

Only 15% glycol means that your coolant has a lower boiling point than the standard 50/50 mix. 60% water / 40% antifreeze used to be recommended as optimal for summer or mild climates.

 

[Astro14]

Changing the thermostat won't change what you're seeing.

Exactly - the thermostat is wide open. Open is open, and lowering the opening point won’t change the temperature at which your van runs on a hot day.

Your cooling system has found the balance point between the heat produced by your engine (and AC) and the heat removed by your cooling system in that ambient temperature.

Want it to run at a cooler temperature?

You need to remove more heat via better air flow, or a better radiator.

You may have scale on this inside of your radiator, reducing its efficiency, or a weak water pump, or this system is just designed with that capacity. Whatever.

If you want the van to run at a lower temperature - you need more cooling, not a different thermostat.

 

[MaximumMini]

When sitting still, any car will heat up until the fans come on. If you want to modify something, it has to be the fan logic. The thermostat has nothing to do with this.

The smart way to control radiator fans is to measure the temperature of the coolant leaving the radiator. When it rises to about 160 that means that the radiator isn't actually dissipating heat, likely because of a lack of air flow. So the fans come on. Many cars have this system but it does require an additional sensor compared to using engine temperature which is already being measured.

Only 15% glycol means that your coolant has a lower boiling point than the standard 50/50 mix. 60% water / 40% antifreeze used to be recommended as optimal for summer or mild climates.

True or false.....Coolant system pressure has the greatest effect on boiling point ?
I ask a lot of question because I like good opinions or facts. sometimes hard to know the difference without lots of asking.

https://macsmobileairclimate.org/2021/04/19/the-pressure-is-on/
A 15 PSI pressure cap twisted onto the radiator will result in a 45°F boiling point increase over the 220°F for a 265°F boiling point.

 

[MaximumMini]

Exactly - the thermostat is wide open. Open is open, and lowering the opening point won’t change the temperature at which your van runs on a hot day.

Your cooling system has found the balance point between the heat produced by your engine (and AC) and the heat removed by your cooling system in that ambient temperature.

Want it to run at a cooler temperature?

You need to remove more heat via better air flow, or a better radiator.

You may have scale on this inside of your radiator, reducing its efficiency, or a weak water pump, or this system is just designed with that capacity. Whatever.

If you want the van to run at a lower temperature - you need more cooling, not a different thermostat.

Google is not always your friend....aka...you can get ANY answer you endorse if you keep searching (right or wrong)

That said, I see many posts on the internet saying that thermostats are not EITHER FULLY OPEN or FULLY CLOSED instantly.
What I'm reading instead is that a thermostat BEGINS to open at it's set point temperature then slowly continues to fully open as temperature continues to rise.

I haven't tested this but I didn't think thermostats were like switches that were either on or off.

This is the reason I was thinking a thermostat with a lower set point might reach FULLY OPEN earlier (at a lower temperature) than one with a higher set point.
Your knowledge and experience is welcomed.

 

[Astro14]

Google is not always your friend....aka...you can get ANY answer you endorse if you keep searching (right or wrong)

That said, I see many posts on the internet saying that thermostats are not EITHER FULLY OPEN or FULLY CLOSED instantly.
What I'm reading instead is that a thermostat BEGINS to open at it's set point temperature then slowly continues to fully open as temperature continues to rise.

I haven't tested this but I didn't think thermostats were like switches that were either on or off.

This is the reason I was thinking a thermostat with a lower set point might reach FULLY OPEN earlier (at a lower temperature) than one with a higher set point.
Your knowledge and experience is welcomed.

OK, well I didn’t Google search for my answer. My answer is based on simple thermodynamics. The amount of heat that your system is able to reject is what determines the equilibrium point.

At 238°, your 195° thermostat is as open as it will possibly be. 180° thermostat will also be open.

You’re not gonna fix this by changing the thermostat, you’re gonna fix this by improving the ability of your cooling system to transfer heat to the ambient air. The reason you have this problem in the summer instead of in the winter, again, is simple thermodynamics. The difference in the temperatures between ambient air and your cooling system operating temperature is what determines how much heat can be rejected to the environment. Again, you’re gonna have to improve the rate of heat transfer. Whether that is replacing parts, or improving parts, that’s what you’re gonna have to do.

Go ahead, stick the 180 thermostat in there. Keep an eye on your temperatures, report back. I got folding money that says it makes no difference.

 

[kschachn]

True or false.....Coolant system pressure has the greatest effect on boiling point ?
I ask a lot of question because I like good opinions or facts. sometimes hard to know the difference without lots of asking.

Reading answers given and understanding them is a good skill too.

 

[LDM]

Just swapping out the thermostat really won't make any difference. You also need to adjust when the fans come on if you want to take advantage of a lower thermostat.

I have 160s in both my Camaros as these cars were setup to run hot for emissions reasons from the factory. Especially the LT1 with its reverse cooling heads. Also on the OBD1 LT1s if you swap to a lower thermostat from the stock 200 it will end up running the fans all the time because the coolant sensor will no longer reach correct temps in the PCM programming to allow the fans to shut off.

Also, these are on modified vehicles, not stock. If you have a vehicle that is stock, changing the thermostat is pretty much pointless. If you have a cooling issue, you need to look into what is causing the overheating, not just swap a thermostat.

 

[Lubener]

Thanks football.
In this case, the vehicle has a new radiator and the condenser and radiator were carefully cleaned recently.
Also, the coolant is fresh and there is no sign of any sludge or contamination in the cooling system. It is maintained with great care.

As far as the fans, the fan relay was replaced and the fans come on (and turn off) at exactly where the Factory Service Manual says they should. I think these particular minivans might simply have slightly undersized radiators.

Sure would have been useful if you mentioned all this in your first post. Heck, change your thermostat and prove us all wrong.

" A failure to communicate".

 

[MaximumMini]

OK, well I didn’t Google search for my answer. My answer is based on simple thermodynamics. The amount of heat that your system is able to reject is what determines the equilibrium point.

At 238°, your 195° thermostat is as open as it will possibly be. 180° thermostat will also be open.

You’re not gonna fix this by changing the thermostat, you’re gonna fix this by improving the ability of your cooling system to transfer heat to the ambient air. The reason you have this problem in the summer instead of in the winter, again, is simple thermodynamics. The difference in the temperatures between ambient air and your cooling system operating temperature is what determines how much heat can be rejected to the environment. Again, you’re gonna have to improve the rate of heat transfer. Whether that is replacing parts, or improving parts, that’s what you’re gonna have to do.

Go ahead, stick the 180 thermostat in there. Keep an eye on your temperatures, report back. I got folding money that says it makes no difference.

Not doubting or arguing.....just trying to absorb info.

 

[MaximumMini]

Sure would have been useful if you mentioned all this in your first post. Heck, change your thermostat and prove us all wrong.

" A failure to communicate".

You could put the entire Bible in your OP.....and someone would say still you left something out.
Life.....Internet.

In all these responses, I still haven't learned if thermostats do indeed open gradually or all at once.
Now that I think about it....I once put a thermostat in boiling water and IIRC, it did not spring fully open like a switch.

Thanks for the helpful post.

 

[MaximumMini]

Lot's of good, helpful info.
Preciate all the replies

 

[MaximumMini]

At 238°, your 195° thermostat is as open as it will possibly be. 180° thermostat will also be open.

What about at 200F? 205F? 210F?
If it doesn't FULLY open until 238F then changing it to open earlier couldn't hurt it seems.

That's what I'm getting at.
That said, the consensus is that it won't make any difference and basically, I believe that to be true

 

[FTTSHO]

If your engine produces enough heat to make the coolant temp that high with a properly functioning cooling system, it’s a cooling issue, not a thermostat issue. Something is going on to allow the coolant to get that hot.

You need to inspect your cooling system and make sure it’s as clean as it can be. If it’s dirty at all, Do a cooling system flush, and put in some good coolant in there. 50/50 mix to ensure proper heat transfer.

I had overheating issues with my 2001 Blazer when I first got it. The thing used to run at 220F, which according to the workshop manual, it’s within the acceptable range. I believe the workshop manual said anything in between 195-225 is fine. But When sitting still with the ac on and the truck not moving, the temp used to go upto 230 and beyond, which is obviously very dangerous for the engine.

The reason was a dirty cooling system that had so much rust buildup from Dexcool and tap water being used by the previous owner. Everything inside the cooling system was coated in brown sludge. Glad I caught it soon enough before warping happened.

Had to use Thermocure Evaporust to clean the system out, and ever since I did that, the truck never overheats, and coolant temp never goes above 205F even in the hottest days with ac on max in stop and go traffic.

Check your cooling system. I just looked it up on google, and it says 195-220 is normal for those. On some newer engines, upto 230 is fine, and it’s one of the reasons why newer engines have higher cooling system pressures of upto 21 psi.

 

[JMJNet]

In addition, try cleaning/washing the cooling stack first?
That usually have the AC Condenser and Radiator together behind the front grill.
Also make sure the Fan are turning on at the correct temperature, before 238F.
I heard the Chrysler/Jeep made vehicle have weaknesses.

 

[Jetronic]

It's not running "hot" according to the factory service manual.
In fact, it runs about exactly where the factory service manual says. But the factory service manual calls for fans to kick on LOW MODE at 224F and to me that just feels too hot.

And I have several of this exact same vehicle. Both maintained like aircraft.
They both run about the same temperature in the Summer

trick the ecu into thinking it's running hotter than it is. should be easy and cheap, a few resistors at most. Or leave it as is.

 

[Chris142]

If you want it to run cooler you need to get the cooling fans to come on earlier.

Either with a manual switch somehow or some kind of scanner you can use to turn them on manually.

 

[Dave9]

In all these responses, I still haven't learned if thermostats do indeed open gradually or all at once.
Now that I think about it....I once put a thermostat in boiling water and IIRC, it did not spring fully open like a switch.

A typical thermostat starts to open gradually at close to it's rated temperature, and if it stays at that temperature, it will continue to open. If the temp rises, it will open faster. A typical design has a wax pellet inside that melts at a certain temperature. Think of it like an ice cube at 32F. It will start to melt at a temp slightly higher, and continue to melt if kept there, and melt faster, the higher the ambient temp is over 32F. The exception is that wax expands when it melts and water expands when it freezes, but either happens over time.

This does not matter much. It will be completely open well before the peak temp reported. If it opened sooner, the temperature would still continue to climb, just a bit slower, until it hit the low fan on-threshold, then continue to climb until the high fan on-threshold, then continue to climb until an equilibrium is met.

As others have stated, this is about radiator and fan performance. If you can't fit a different radiator with improved performance (more rows or thickness) then you need more fan performance (# of fins or motor RPM or an additional fan, or measure the voltage getting to the fans in case the old wiring and connectors are dropping some voltage).

For example I looked up radiators for a '99 Caravan and some have one row but others two like this one:
https://www.rockauto.com/en/moreinfo.php?pk=2675658&cc=1353967&pt=2172&jsn=724

 

[Mechanician]

Sitting at idle in traffic vs. highway driving, the volume of coolant moving through the thermostat is night and day.
The incremental difference in thermostat opening is a non factor, once the engine is fully warmed up.

You can easily test a thermostat's opening temps, and how fully it opens at what temperature, to your hearts content.
Put it in a large mug of water and -
Add an immersion water heater like this

And a candy thermometer like this

 

[97prizm]

Got a Dodge minivan.
Factory Thermostat = 195F
Current thermostat = 195F
Runs a bit warm in the Summer only when sitting still on very hot days in traffic or at long red lights etc.
When moving it seems to do fine.

Sitting still in traffic Max temp = 224F-228F (fans kick on, temp drops back to 212F, then rises again...repeat)
Moving = 197F-205F

228F seems too close to 260F (purely opinion) and I'd like to see it hover a bit lower when sitting in traffic etc.
But installing a thermostat will probably give me temps under the 195F specified for this engine when moving. (If radiator has the capacity)
Would installing a 180F - 190F thermostat help (or hurt)?

I'd flush the radiator out with prestone radiator cleaner. Then check the fins. Some vehicles don't have great cooling so a twin row radiator if it'll fit could help