Thermostat opinions - Lower Set point for Summer

i had a ford that kept over heating. new tstat, new radiator, fans worked.

took the heads off, and holy god the amount of crud and deposits down around the cylinder bore. Absolute nightmare to clean out. Water/coolant was never getting down around where it was actually needed.

and in theory, fans are only needed if water exchange from thermostat opening with the radiator isn't enough. ie, stopped in traffic, no air flow. Clutch fans are kinda of a thing of the past. Everyone uses those cheap electric fans now. all about them MPG.
 
tblt44 said:
35 years ago I used to drill 2 small 1/8 holes in the flange so when it was closed it still slowed slightly.
Did it help couldn't tell.
But in my mind if my thermostat ever stuck closed I would have some water circulating to help prevent overheating
Click to expand...
That was a trick many used to deal with air pockets behind the thermostat when the thermostat was at the highest point in the cooling system and the thermostat had no jiggle valve. . I did it on my 1992 Dodge 2.5 engine. Those holes will not prevent overheating if the stat stuck closed. . Not nearly enough water flow through those 1/8 inch holes, just enough to allow an air pocket to pass by and prevent overheating due to an air pocket behind the thermostat.
 
I once drilled a hole in the thermostat of a 90's Nissan I had. It took noticeably longer to warm up in the winter. My dad used to hold the thermostat open with an aspirin tablet to aid in filling the cooling system. He said he learned it from his dad (who was a Buick and Studebaker mechanic).
 
The vehicle is not overheating. It is working exactly as the mfr designed it to. There are many, many of these vans on the road, all functioning the same way, with a whole lot of them achieving a very long life. Absolutely nothing to worry about.
 
zrxkawboy said:
The vehicle is not overheating. It is working exactly as the mfr designed it to. There are many, many of these vans on the road, all functioning the same way, with a whole lot of them achieving a very long life. Absolutely nothing to worry about.
Click to expand...
And that’s what the OP stated.
 
ripcord said:
Basically, after reading this thread, it sure seems to me that there is nothing wrong with the cooling system of @MaximumMini's van. He merely has a disagreement with the manufacturer about what the appropriate temperature is to turn the fans on and off. Have you tried turning the AC on to force the radiator fans on? If you don't want the cabin cooling from AC, you can also turn up the temperature on the heater to compensate.

The simplest way that I can think of to MacGyver an override of the ECU logic without a custom tune would be to install a small resistor or potentiometer inline on the temperature sensor signal wire. Maybe in the rage of 5 to 25 ohms. I'm guessing you'd want to reduce the voltage in the range of tenths of a volt. The normal theory of operation in most cars is that the voltage returned by the sensor goes down as the temperature goes up, so pulling the voltage lower with a resistor will trick the ECU into seeing a higher coolant temp and turn the fans on and off at a cooler temp. You would probably want to put this resistor on a manual switch for hot days as it would also have the effect of causing the ECU to keep it in open loop longer during warm up and running slightly richer at times.

This idea only works, BTW, if the sensor is a conventional that returns a voltage based signal.
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Yeah I fell for one of those years ago. It was a resistor potted in a small 1 inch cube with two leads sticking out with heat shrink. Splice in-line with radiator temp sensor/switch. Fools the ecu to get the fans to come on sooner
 
Correct.
Basically the system is working as designed. It's my preference to change it somewhat.

Why? Because ALL environmental and personal factors cannot possibly ALL be accounted for with one cooling system design.
I happen to live where it never gets below freezing and is often over 100F in the Summer. The manufacturer has to accommodate averages or majorities and not specifics. Driving this exact same vehicle year round in Canada would differ from driving it in South Florida.

1). Sitting for extended times causes the coolant temp to rise as high as 224F-228F before the fans come on at low speed (still acceptable according to the FSM), however, at that temperature the condenser is unable to achieve sufficient condensing of the refrigerant gas resulting in loss of AC cabin cooling. That same design turns the fans back off at 215F.
Imagine having medical conditions that are affected by high heat and then being forced to sit in a vehicle (roadway emergency etc) with no AC, no shade and no breeze on a day where the ambient is 105F and the cabin of the vehicle quickly reaches 120F with doors and windows open.

2). At 230F, while acceptable (so is 20k mile oil changes), some lubricants reach their lower threshold of chemical degradation. In addition, head gaskets begin to degrade around 260F and 230F+ is only a very small leak in the coolant system away from boil over and potential head gasket damage. why live near the edge?

In my case (Tropical weather climate) the solution seems to be to add an adjustable fan controller along with a higher flow rate thermostat, lower ratio of antifreeze and a HD 2 row radiator (factory was 1 row radiator).

If you live in a Tropical climate and drive an older vehicle (or newer), you may have already done some or all of these.
If you live in a Northern harsh winter climate your needs and methods will vary.

Very helpful discuss and I appreciate all responses. Hope we all got something from it.
 
Last edited:
factorytuned2012 said:
Yeah I fell for one of those years ago. It was a resistor potted in a small 1 inch cube with two leads sticking out with heat shrink. Splice in-line with radiator temp sensor/switch. Fools the ecu to get the fans to come on sooner
Click to expand...
Yes, this has been a common "mod" for a long time on many vehicles. While it works, I don't recommend it. Reprogramming the ECM/PCM is the best option as you have full control over the exact temperatures. Although it does tend to be a bit pricier than a resistor I suppose.
 
MaximumMini said:
Correct.
Basically the system is working as designed. It's my preference to change it somewhat.

Why? Because ALL environmental and personal factors cannot possibly ALL be accounted for with one cooling system design.
I happen to live where it never gets below freezing and is often over 100F in the Summer. The manufacturer has to accommodate averages or majorities and not specifics. Driving this exact same vehicle year round in Canada would differ from driving it in South Florida.

1). Sitting for extended times causes the coolant temp to rise as high as 224F-228F before the fans come on at low speed (still acceptable according to the FSM), however, at that temperature the condenser is unable to achieve sufficient condensing of the refrigerant gas resulting in loss of AC cabin cooling. That same design turns the fans back off at 215F.
Imagine having medical conditions that are affected by high heat and then being forced to sit in a vehicle (roadway emergency etc) with no AC, no shade and no breeze on a day where the ambient is 105F and the cabin of the vehicle quickly reaches 120F with doors and windows open.

2). At 230F, while acceptable (so is 20k mile oil changes), some lubricants reach their lower threshold of chemical degradation. In addition, head gaskets begin to degrade around 260F and 230F+ is only a very small leak in the coolant system away from boil over and potential head gasket damage. why live near the edge?

In my case (Tropical weather climate) the solution seems to be to add an adjustable fan controller along with a higher flow rate thermostat, lower ratio of antifreeze and a HD 2 row radiator (factory was 1 row radiator).

If you live in a Tropical climate and drive an older vehicle (or newer), you may have already done some or all of these.
If you live in a Northern harsh winter climate your needs and methods will vary.

Very helpful discuss and I appreciate all responses. Hope we all got something from it.
Click to expand...
Whenever the A/C is running - the fans should be running - regardless of the coolant temperature.
The Condenser is in front of the radiator, and condensing should not be affected by the coolant temperature.
The only time the fans should turn off with the A/C turned on is if the cabin temperature, or the evaporator temperature calls for the entire system to cycle off.
 
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Yes if you start the engine cold on a hot day and set the A/C for maximum cold with the car sitting still, the fans should start almost immediately.
 
Mechanician said:
Whenever the A/C is running - the fans should be running - regardless of the coolant temperature.
The Condenser is in front of the radiator, and condensing should not be affected by the coolant temperature.
The only time the fans should turn off with the A/C turned on is if the cabin temperature, or the evaporator temperature calls for the entire system to cycle off.
Click to expand...

What mechanism ensures that?
Are you absolutely certain that applies to all vehicles?

Reason I say this is I have two identical Gen3 Chrysler minivans. Both have outstanding ice cold AC.
Neither of them exhibit that behavior (the fans on neither come on when the motor is cold with the AC on.)
The fans work precisely according to the Factory Service manual for this vehicle.

How would you explain that?

The only thing I can think of is that perhaps even though the AC is ice cold, it's possible the system could need a bit of refrigerant, meaning the pressure is below the AC pressure transducer minimum on set point. I could attach gauges to check this and probably will.
Odd that both of them would have to be at almost the exact same point of "low freon" to not trigger the AC clutch AND to keep the vehicles ice cold on even 100F+ hot summer days.
 
What are you saying there? The fans must run as needed for A/C operation regardless of coolant temperature. There are parallel paths of control.

There is no way you get "ice cold" air with the car sitting still without the condenser fans running. That is just physics.
 
mk378 said:
What are you saying there? The fans must run as needed for A/C operation regardless of coolant temperature. There are parallel paths of control.

There is no way you get "ice cold" air with the car sitting still without the condenser fans running. That is just physics.
Click to expand...

Not exactly true.
Efficiency will suffer on a linear basis along with rising heat, but you most certainly can get AC operation without the fan running (until the refrigerant pressure transducer trips the AC clutch cut off point)

So before the refrigerant gets hot, you can still get ice cold air. But when I said "Ice Cold Air" I actually meant they are capable of Ice Cold Air when moving or when the fans do come on. Not sitting still indefinitely.
 
MaximumMini said:
What mechanism ensures that?
Are you absolutely certain that applies to all vehicles?

Reason I say this is I have two identical Gen3 Chrysler minivans. Both have outstanding ice cold AC.
Neither of them exhibit that behavior (the fans on neither come on when the motor is cold with the AC on.)
The fans work precisely according to the Factory Service manual for this vehicle.

How would you explain that?

The only thing I can think of is that perhaps even though the AC is ice cold, it's possible the system could need a bit of refrigerant, meaning the pressure is below the AC pressure transducer minimum on set point. I could attach gauges to check this and probably will.
Odd that both of them would have to be at almost the exact same point of "low freon" to not trigger the AC clutch AND to keep the vehicles ice cold on even 100F+ hot summer days.
Click to expand...
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.

 
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