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Two summers ago I was forced to change the thermostat in my 1997 Acura Integra LS. It turned out to be a really difficult problem to diagnose because even on the hottest of days it would only overheat when left to idle. Going down the road it would always stay within a normal range of operation.
Changing the thermostat got rid of the overheating in summer problem but it created a new problem of discomfort in winter. The new thermostat was set to the factory recommended 170 degrees. Problem is that that doesn’t allow the car to get really warm in the winter. As days start to cool down, it’s reflected in the operating temperature of the engine until I get to the point that the temperature needle never gets above cold and cabin temperature remains just cold.
I’m tempted to get a NAPA 195 degree thermostat, but I have my reservations about deviating from the manufacturer deemed was the best thing. 170 degrees just seems too cold for winter, but would 195 be too hot for summer. I don’t want to be swapping thermostats back and fourth all the time. Is it more likely that my 170 degree thermostat is never closing.
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I don’t know of any manufacture that recommends a 170f thermostat. Most are 195f. I would buy one from the dealer anyway. In my experience NAPA thermostats are junk.
Your thermostat is stuck open to some extent or failed in some other way. It being 170 sounds already will keep the heat from being the best, but the engine isn’t warming up because the stat isn’t holding coolant back from flowing thru the radiator before it gets to 170. It’s supposed to be closed until the coolant is hot enough to make it open and allow it to be cooled by the radiator. There is normally a small hole in a lot of thermostats that allows some bypass but nowhere near enough to prevent an engine from warming up.
Also 2nd what wysetech said.
NAPA thermostats are made by “Stant”.
I should know, I just replaced the one in the bronco. And yep, just a stant thermostat in a napa box. (It has the name “Stant” physically imprinted into the metal.)
In most cases, unless the cost is at issue–I usually use OEM. The Beetle I also drive? Has a VW thermostat.
One of the hidden issues with thermostats is not getting stuck open or closed. It’s having the spring get weak. And then you’re thermostat is regulating the engine just slightly colder then it’s supposed to be. Result? Oddball CEL’s that make no sense, and yep…It can even kick the air/fuel ratio enough to trigger P0420 codes.
This is easy to verify with a scan tool that shows live data. On our car, it’s rated 95c That boils down to about 205F (203 actually) So when trying to chase down the issues? I hooked VCDS into the system (it’s a clone of VW’s own software) and watched the temp as we drove. Sure enough. It hovered around 180-190. Tested and found the thermostat was opening to early.
Point being (Yeah, there’s a point) It’s always best to use an OEM temp thermostat. I’m not going to say NAPA/Stant thermostats suck. Cause they really don’t. But you do have to change a thermostat as normal maintenance every few years. Nothing lasts forever.
If you are concerned about the engine temp, best bet is to use a scan tool to monitor the temps as being reported by the system. There are soooo many reasons for running to cold or hot.
Eric did a great video on overheating. But it’s also important to know that running to cold, really knocks down your MPG, and stresses out the engine. (They build it to run at an exact temp range.)
If you replace it with a quality OEM thermostat–and the engine overheats–Then you have an issue to figure out. Just dropping in a lower temp stat is covering the issue up.
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My car has a 176 degree thermostat and it was built to be a track car. So, I’m having trouble believing 170 degrees is correct too.
However, something is wrong with your cooling system. Are the fans working, no junk in the radiator or condenser, is the cooling system full?
Your car is old enough to have had the radiator replaced at least once. Maybe whoever chose the last radiator went a little too cheap.
Anyway, I agree, get an OEM thermostat. It will be the right one and it will work.
Unless you have a modified engine(and I mean really modified like mine is with cam, headers, forged
internals, modified carb jets and clearances, etc…, then i would ALWAYS use the recommended stat temp
from the factory specs. As others have said I find 170 degrees to be too cool for the engine and no
manufacturer I know of uses that temp as a spec either as wysetech has said. I disagree with the
NAPA(Stant) opinion however as I have used Stant thermostats in my own and many other customers vehicles
and never ever had a problem. Plus they are made in the USA the vast majority of the time while if you
get an OEM stat it may be made elsewhere(Im anal about USA made stuff not everyone is). This is just speaking from what I have
experienced with the brand and not everyone may have had the same experience.
170 degrees coolant will give you plenty of heat winter time. It’s 170, not 70. Hence, as others mentioned, you have a flaw somewhere in your cooling system.
Firstly, I think your heater is not receiving hot coolant. Likely due to un purged air. That it does not overheat with air bubble in it is possible, as Honda has quite extensive coolant plumbing and it may be simply bypassing heater.
Secondly, t-stat is either stuck open or set crooked in the seat, allowing excessive by flow.
Thirdly, worse come to worse, place a piece of cardboard in front of radiator. Full or partial coverage. This reduces air flow on fins, and keeps coolant warmer.
But I’d have started with proper system bleeding procedure.Who or what source told you that any OBD II car would use a 170º thermostat? The wrong thermostat can affect loop status, emissions, and fuel economy. Overheating at idle is a really good sign that your cooling fan(s) aren’t working. Regardless of any brand you decide to buy, get a 195º thermostat back in it. Eric’s got a good video for bleeding air out of the cooling system. Then start diagnosing the actual root cause of your overheating problem.
I agree with no_common_sense and you really need to get that 170 out of there.
If your engine is overheating at idle then you need to make sure the cooling fans are operating as they should be and also that they don’t appear to be dragging due to wear.
An update:
The thermostat was what was wrong with my car when it was overheating two years ago. For whatever, reason the fans were not coming on and it would seem that the thermostat was stuck closed to some extent. When I replaced the thermostat, the fans kicked in at proper temperatures and it kept itself cool. My theory was that the fan sensor is outside the thermostat and since it was not opening the fans never sensed enough heat to trigger. It seems far fetched but the fact remains that no cooling fans were part of my problem and changing the thermostat magically fixed the fans.
I highly suspect anything is wrong with the cooling system elsewhere on the car. I’ve driven up mountains with the AC on 90+ degree days and never had the engine temperature get above half.
The 170 degree figure comes from all aftermarket sources of thermostats. Oreilly will only sell me a 170 degree thermostat “set to manufacturer standards.” Same at Autozone, with Napa recommending the 170 while making available a 180 and a 195.
I know that the problem isn’t a bubble because I have good heat when it isn’t that cold. 40 degree day, I’m inside warm and toasty. But I’ve been on long drives up north that as it gets colder outside my vent heat fades away along with the engine temperature gauge. (It’s not like the air ever gets cold but it isn’t hot and loses pace with heat lose.) So it isn’t like the plumbing is blocked. It’s just like the engine runs out of heat to give.
EDIT:
Reading around, I’m realizing that it’s rare that anybody loses temperature once the car is already warm. What exactly does this mean? Do car thermostats typically open and close all that much while a car is going down the highway? I guess I’ll order a thermostat from Acura and hope that that solves my problem.
Thermostats are constantly changing position almost all the time once you are at operating temp, constantly working to keep the coolant at a consistent temperature. It is infinitely variable, it doesn’t have notched positions like a switch or gear shifter where it might be open, half open, or closed.
If you don’t have one installed or it’s open all the time, almost all the coolant goes thru the radiator all the time. It only warms up if you don’t have airflow over the radiator or you create a lot of heat by demanding power from the engine. If left unchecked by the thermostat, it will usually not get hot because stock radiators can usually dissipate more heat then most drivers will cause the engine to produce.
The thermostat is actually there more to keep make the system hot, not cool it down. If your coolant isn’t hot, you don’t have good heat but you also make more emissions. It blocks flow to the radiator until the coolant gets hot enough.
Just writing the follow up (Cause I always want to know the end to every story.)
I purchased a Honda thermostat and gasket, and took it apart last evening. When I opened it up, I could immediately see that the gasket around the thermostat was all chewed up so my premise is that when I installed it last year I either didn’t replace it or fit it correctly when I put it back together and coolant was flowing through the radiator with very little to stop it.
The Stant thermostats I used to use all came from Mexico. I say used to use because I had problems with them. However, the other day I needed a thermostat and was in one of the automotive chain stores. Well, you know how it goes, one for $5, one for $10 and so on. I asked for their premium thermostat and got a Stant. However, to my amusement, it was made in Germany. Hopefully, the Stant people are learning their lesson.
BTW, the OEM thermostat for this car is still 180 degrees. I looked up the spec.
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