Faulty thermostat not always obvious, but can cause problems
Dear Ask A Mechanic,
I have a recently purchased 2014 Chrysler Town and Country with 185K on it.
Engine light is on, code reader says, 'P0128.'
The internet says the code more than likely is a bad thermostat. Did some basic research on YouTube academy and it looks like an easy fix. However, since I don't know what coolant the previous owner used, should I use this opportunity to do a full coolant flush? I read online that it's bad to 1) use universal coolants because they're a lie and 2) you shouldn't mix coolant brands.
Bottom line: Do I just do a coolant flush with a thermostat swap for the P0128 code? Keep track of what coolant was used from here on out, or can I just top off with the correct coolant for the vehicle make and model and be fine?
Van About Town
That trouble code, P0128, is defined as 'Engine Coolant Temperature Below Thermostat Regulating Temperature.' There are actually a variety of reasons why that DTC (diagnostic trouble code) might set, including a low coolant/antifreeze level (which can cause false temperature readings, as air doesn't conduct heat as well as liquid, fooling the sensor), or a failed coolant temperature sensor, itself.
Most commonly, though, it's because there legitimately is a problem with the engine coolant thermostat — usually just referred to as 'the thermostat' — that is preventing the engine from reaching its full operating temperature as quickly as it should (or at all).
The main purpose of the Check Engine light is to inform the driver of issues that can increase emissions levels.
This is actually the case for the thermostat.
Engines are most efficient and perform best within a reasonably narrow temperature range. Too hot and internal components can get damaged, too cold and the engine must use a richer mixture — that is, one with a higher ratio of fuel to air than ideal — in order to maintain reliable combustion and acceptable performance.
Richer mixtures result in a higher amount of unburned fuel entering the exhaust, and increase levels of carbon monoxide being produced.
Prolonged or regular use at low engine temperatures has other detrimental effects, including accelerating engine wear and contaminating oil.
But the light is on as a pollution warning.
It's quite possible that you might not notice any difference in heat output or a lower reading on the gauge. The engine computer has a much closer eye on things. It knows what temperature the coolant was at during start-up and the air temperature, what operating conditions the engine saw and for how long, and beyond seeing what temperature the coolant reached, it can calculate whether it reached a specific temperature quickly enough.
Fortunately, as you note, the thermostat is quite easy to replace on Chrysler's 3.6 litre V6. Just be sure to bleed the air out of the system correctly.
This would be the perfect time to change the coolant, and you'll know where you stand afterwards. The factory coolant is Mopar's '10 Year' purple, which is overdue for changing if it's still original.
Universal coolant/antifreeze is a fallacy as far as I'm concerned due to the contradictory chemical properties different coolants possess, and while equivalent products from many brands are fine to mix, mixing types is never a good idea.
If in doubt, get it out!
Keep in mind that simply draining the rad won't get all of the coolant out, given what will be trapped in various places including the rear heater system and its plumbing. Without access to an exchange-type flush machine, you may have to do a second spill-and-fill later if you determine that the coolant is, indeed, obviously contaminated.
Ask a Mechanic is written by Brian Early, a Red Seal-certified Automotive Service Technician. You can send your questions to
wheels@thestar.ca
. These answers are for informational purposes only. Please consult a certified mechanic before having any work done to your vehicle.
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Faulty thermostat not always obvious, but can cause problems
Dear Ask A Mechanic, I have a recently purchased 2014 Chrysler Town and Country with 185K on it. Engine light is on, code reader says, 'P0128.' The internet says the code more than likely is a bad thermostat. Did some basic research on YouTube academy and it looks like an easy fix. However, since I don't know what coolant the previous owner used, should I use this opportunity to do a full coolant flush? I read online that it's bad to 1) use universal coolants because they're a lie and 2) you shouldn't mix coolant brands. Bottom line: Do I just do a coolant flush with a thermostat swap for the P0128 code? Keep track of what coolant was used from here on out, or can I just top off with the correct coolant for the vehicle make and model and be fine? Van About Town That trouble code, P0128, is defined as 'Engine Coolant Temperature Below Thermostat Regulating Temperature.' There are actually a variety of reasons why that DTC (diagnostic trouble code) might set, including a low coolant/antifreeze level (which can cause false temperature readings, as air doesn't conduct heat as well as liquid, fooling the sensor), or a failed coolant temperature sensor, itself. Most commonly, though, it's because there legitimately is a problem with the engine coolant thermostat — usually just referred to as 'the thermostat' — that is preventing the engine from reaching its full operating temperature as quickly as it should (or at all). The main purpose of the Check Engine light is to inform the driver of issues that can increase emissions levels. This is actually the case for the thermostat. Engines are most efficient and perform best within a reasonably narrow temperature range. Too hot and internal components can get damaged, too cold and the engine must use a richer mixture — that is, one with a higher ratio of fuel to air than ideal — in order to maintain reliable combustion and acceptable performance. Richer mixtures result in a higher amount of unburned fuel entering the exhaust, and increase levels of carbon monoxide being produced. Prolonged or regular use at low engine temperatures has other detrimental effects, including accelerating engine wear and contaminating oil. But the light is on as a pollution warning. It's quite possible that you might not notice any difference in heat output or a lower reading on the gauge. The engine computer has a much closer eye on things. It knows what temperature the coolant was at during start-up and the air temperature, what operating conditions the engine saw and for how long, and beyond seeing what temperature the coolant reached, it can calculate whether it reached a specific temperature quickly enough. Fortunately, as you note, the thermostat is quite easy to replace on Chrysler's 3.6 litre V6. Just be sure to bleed the air out of the system correctly. This would be the perfect time to change the coolant, and you'll know where you stand afterwards. The factory coolant is Mopar's '10 Year' purple, which is overdue for changing if it's still original. Universal coolant/antifreeze is a fallacy as far as I'm concerned due to the contradictory chemical properties different coolants possess, and while equivalent products from many brands are fine to mix, mixing types is never a good idea. If in doubt, get it out! Keep in mind that simply draining the rad won't get all of the coolant out, given what will be trapped in various places including the rear heater system and its plumbing. Without access to an exchange-type flush machine, you may have to do a second spill-and-fill later if you determine that the coolant is, indeed, obviously contaminated. Ask a Mechanic is written by Brian Early, a Red Seal-certified Automotive Service Technician. You can send your questions to wheels@ . These answers are for informational purposes only. Please consult a certified mechanic before having any work done to your vehicle.
