420A 160 Degree Thermostat

[BLACK'98DSM]

My car stil has the original thermostat in it. At 25 years of age I figure it's time for replacement this spring. I see that the original is a 185 degree thermostat. I'm wondering if it's a good idea to use a 160 degree thermostat. It's not a daily driver and I run it hard sometimes. With the 160 being the same price as an OE rated one, I don't see why not?

 

[007jimmy]

Stick with the OEM thermostat. The lower temperature unit does nothing but delay the closed loop function on the ECU. Unless you live in a extremely cold environment your car will always eventually warm up to factory settings until the fans come on.

Now if you aren’t using the stock ECU then you can probably tune around it.

 

[1995TalonMT]

A really fun test is to put the old thermostat in water on the stove with a thermometer and read the temperature as it opens...you can see it as it opens visually. Some are just stuck in one position after all that time that is what I found on one of my vehicles. I went with the original temperature thermostat as the ECU uses coolant temperature as one of the input considerations for fuel delivery therefore the coolant temperature sensor (to ECU) is also critical.

 

[Mech Addict]

Ultimately the thermostat can only open all the way. If you're running it hard, that will happen whether it's 185 or 160 rated. In fact, the coolant temp is likely to be higher than either of these setpoints. Using it for road racing, I would think you could just leave it out entirely, and make sure you warm up the car enough before the race. Of course for street use you'll want a thermostat.

 

[97egl]

Stick with the OEM thermostat. The lower temperature unit does nothing but delay the closed loop function on the ECU. Unless you live in a extremely cold environment your car will always eventually warm up to factory settings until the fans come on.

Now if you aren’t using the stock ECU then you can probably tune around it.

I'd have to disagree with this. I run a circle track car and if you are running a car hard you're normally going fast enough to keep the airflow going thru the radiator cooling the coolant down so when the thermostat is opening determines when the radiator exchanges water with the engine and cooler thermostats have always kept my cars running cooler. I have my fans on a toggle switch and they only get put on during a yellow flag and on pace laps.

However for any car that is not a purpose built racecar I would highly recommend using the OEM thermostat. I do agree that you want to get to closed loop on the ECU as quick as possible and really all low temp thermostats do on a street car is make your mileage suffer. You have to be going HARD for an while on a car to make it overheat with a properly functioning engine and cooling system

 

[007jimmy]

I have my fans on a toggle switch and they only get put on during a yellow flag and on pace laps.

So the temperature does go up eventually like I stated. OP never stated circle track racing. Normal traffic driving or any stopping of the car will have the temperatures rise. There’s no debate that constant cruising will keep temps down if the coolant system is up to par.

However for any car that is not a purpose built racecar I would highly recommend using the OEM thermostat. I do agree that you want to get to closed loop on the ECU as quick as possible and really all low temp thermostats do on a street car is make your mileage suffer. You have to be going HARD for an while on a car to make it overheat with a properly functioning engine and cooling system

This is all I was saying. So there is no point in going to a lower thermostat temperature unless you can tune around it.

 

[Mech Addict]

He didn't emphasize the racing, but it is on his car icon at the bottom of each post. It does say "sometimes" runs it hard, which does imply a fair amount of street use, even with that WRX in the stable. I would think that having to keep an eye on the temp gauge and toggle the fans manually while racing would be a distraction with other drivers on the track doing unpredictable things. Wouldn't there be a simple way to have a cts setpoint control them? Then the fans would act in place of the thermostat to a large extent. Perhaps the non-turbo nature limits the power (and heat) to a level that doesn't need much improvement to begin with. What would you guess is the hp of this car? Or is it the case that the temp sometimes goes too low to stay in closed-loop? I'm not sure what I'm thinking anymore...

 

[jesse12345]

I ripped my talon hard last summer about 80 to 90 degree days with a 160 and without fans and it never overheated. I'm assuming stop and go traffic itd probably get up there. This was with a turbo though I don't know if that'd change anything much.

 

[Mello]

My suggestion is to stay with the OEM temp thermostat. Cooling systems are to keep the operating temps within a set range for best performance. The thermostat controls the low set point & the radiator & fans control the high set point. The fans only help at low speeds. If you're having high temps you would want to look into the radiator & how to improve it's efficiency with ducting to create a higher pressure drop across the core. Increasing the radiator capacity will only delay heat soak time but will eventual things will run hot.

 

[Adam]

This probably doesn't apply to a 420a but my 4g actually developed a slight miss when running a 160. Swapped back to a 180 and it never did it again.

On a different note and obviously there's alot of different variables here but a lower temperature thermostat can actually make it easier for your car to overheat. In example, 100 degree outside and 160 thermostat .. thats only a 60 degree difference in air temperature to cool your radiator where as 100 degrees outside and 180 thermostat .. that's an 80 degree difference. This stuff has a lot of variables but it's an interesting concept that most probably wont deal with.

Also remember that you want your engine to get warm. Your engine functions better hot then cold. Your oil needs to get above around 210 to burn off contaminants, condensation etc.

So like others have said, its best to keep the stock temp thermostat. The ecu already has programmed settings setup around that temp.

 

[Mech Addict]

not sure I agree with your math... the temp rating of the thermostat is simply when it should fully open. If it's hot out (100) and your car is making a lot of heat and raising the temp of coolant, it will be fully open by 180 in either case. Though I do agree that a cold engine is not efficient, and the ring/cylinder wear is actually much more rapid at lower temps.