I know there are no stupid questions, only stupid people who ask these questions: Why are there different heat ranges for thermostats (160-180-195)and for what purpose would you choose a particular one? Just tryin' to gain a little knowledge, here. Thanks.

JR

the rating is the temp at which you want the thermostat to open.

in general the lower the numbers the cooler the engine runs..

depending on the application cooler is usually better.. but modern engines dont run right until the temp is higher.

The short answer...

Cars are made to run optimally at a certain temperature. A thermostat helps the engine reach this temperature quickly.

It also helps the engine maintain this temperature in colder climates.

Without getting into water chemistry, metal expansion properties, fuel vaporization principles or airflow techniques...

In the south you may want to go with a 160 degree thermostat. Because your engine runs hotter than that normally and the outside temp never gets really cold, might as well let the water flow in your engine at 160 degrees.

In the north either a 160 or 180, depends on if it gets cold enough to make your engine not reach 180 degrees.

In the Artic, maybe you'd want to go either 180 or 195 to try and get your engine to reach a normal operating temperature.

Maybe others can chime in with the long detailed theory on thermostats.

Thanks, Guys...got my answer. So for a semi hi-perf engine (400-450 hp) in sweltering So. Florida, a 160 rating would be the choice. Lower temp = more hp. COOL!

JR

There is a bit more to it than that. Here is another one of my short answers.

First, if you have a computer controlled car use the OEM temp stat. This is usually 195 deg. The computer is sensitive to the engine temp and will respond in a negative way if the engine remains too cold. You lose fuel mileage and raise emissions, and can sometimes set computer failure codes and affect performance.

Now for non-computer cars.
The first myth is the t-stat control the upper temp of the engine. It does not. It controls the minimum operating temp. If the engine is running at 200 it is going to run at 200 no matter what t-stat it has. The temp rating is when it opens. If the car is running at at the rated temp, the stat keeps it there. But if the engine gets to 200 it does not matter if the stat is a 160, 180, or 195. Once it's open, it's open. As long as it's warm enough to stay open it is a constant restriction and has no more affect on coolant temp. It will only change when the engine cools down to the stat temp, and the stat starts to restrict flow to control heat. Then it will hold it at that point.

If the car runs normally at 185, the 180 or 160 stat will still find the car running at 185. But the 195 stat would raise and hold the temp at 195.
The only thing that controls the top end of the temp once it exceed the stat temp is the cooling system operation. The more heat it removes the cooler it stays. The more heat the engine produces, the hotter it stays. It's a balancing act. Heat production vs heat dissipation. Don't forget to figure ambient temp in this formula. As ambient air temp raises there is less difference between air and radiator, so less heat is removed.

Now for the other end of the scale.
Any engine has what is called quench areas. The quench area is designed into the engine to help control the way fuel burn in the cylinder. It is an area that is cooler than the other sections of the cylinder, and thus affects the rate of fuel burn. It also affects the total burn rate and completion of burn in the cylinder. The hotter the engine and coolant, the less quenching.

If the engine is too cool, the fuel gets overquenched and combustion suffers. This results in lack of power, and poor mileage, and high emissions. You can feel this in every engine while it is warming up from a cold start. They run bad cold compaired to warm. This is due in a large part to quenching.

If the engine is not quenched enough you have uncontrolled burn. This can cause pinging, knocking, lack of power, and backfire.

You need to find the right combination. Higher compression engines can run cooler due to the compression itself creating heat in the cylinder. The two balance out.

One way to create a different enviroment in the cylinder is to change the heat range of the spark plug. A cooler engine can run a hotter plug. A hotter engine can run a cooler plug. While it does compensate for some cylinder conditions, it cannot compensate for quenching, as that is built into the engine and cooling system design. But it does offset the effect of quenching to a degree. A lower temp stat may require a hotter plug, and vice/versa. Choosing the wrong combination can make the plugs burn out, or foul out. Due to the higher heat of higher compression, high compression engines tend to run cooler heat range plugs.
Valve size and opening also have a large affect due to the changing air flow and swirl in the cylinder. Intakes and headers also affect air flow.

Generally speaking, for a non-compuer fairly stock car it can run best around 180 to 190. If my 75 C3 runs there when I get it on the road, I'll be happy. But some of the older or custom built engines run better around 160. It comes down to engine design, spark plugs, compression, fuel, and how the car is typically driven as to the best for your application.

i run 160 in my vette (no winter driving) and it runs around 175-180... (195 without water wetter)

my truck is 160 in the summer and 180 winter and it runs around between 160 to 190 depending on the day and the load during the summer.. runs a very consistent 180 in the winter..

both of these are non-stock..

i will add that my truck doesnt have enough cajones to run a 160 in the winter and when i run a 180 in the summer it tends to run a little too hot.

but with your 400 hp engine and southern locale.. your probably a good canidate for a year round 160

|UPDATED|6/30/2004 6:57:10 PM (AZT)|/UPDATED|

ken,
Will running colder plugs in an engine that seems to run hot(around 195 when warmed up on a hot day ) make the temp drop a little?
If so, do you specify the coldest plug at the parts store?

It may run slightly cooler. But it may not. Due to poor combustion and opening the throttle more, it may actually run hotter. While this is not likely, and in fact unusual, it is possible.

The heat range of the plug does have a drastic effect on combustion, but not a lot on engine temp, except due to the combustion temp. If combustion get too cool, regardless of engine temp, performance will suffer. The flip side is the engine temp does have a large effect on the required heat range of the plug.

I would not go to the coolest heat range right away. Go down one step at a time and experiment. If the plugs start to foul or performance suffers, go back up one.

Different plug mfgs rate their plugs in different ways. For some of them you will need to look in one of the catalogs and decode the plug.
AC Delco plugs are printed with the heat range. A R44T is one heat range up from a R43T. The number is the heat range. Other brand plugs are not as easy to read. You may need the chart in the catalog. Don't relay on most parts persons. A few know, but most don't. There computer won't list the charts, ask them to get out the catolog.

Too high of a heat range can actually damage the engine. In some cases causing major failure, including holes melted in the pistons.

I'm printing this..thanks, all.

JR

Ken,
my reason for asking about the plugs is two fold. I am running hot and fouling plugs. I have two 4 barrels and I wonder if changing to a high voltage ignition system ( like an MSD) would help combustion and prevent the plugs from fouling.I have downsized the main jets in an attempt to correct an over rich situation ( my power valves have been blocked off because of the neg. vac of the blower ).
Any thoughts?