180f thermostat for the Chrysler 3.3l V6?

Take a look at this coolant system schematic and flow daigram right out of the '99 LH FSM:

Again, I think the design intent is for the fans to be the main determining factor, not the thermostat.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Link's NG

Oops - Thanks Jim! I used the URL that works for externally linking from a forum, and didn't think to check that it worked after posting it. Different URL for clicking. Let's see if this works:

Jim Shulthiess wrote:

"Bill Putney" wrote > Oops - Thanks Jim! I used the URL that works for externally linking

Seems like rather an odd setup to me. Water doesn't flow until the radiator cooled fluid reaches a predetermined temp. I guess it makes sense to assure engine temp rises to an efficient level asap, but it sure is backwards to this old phart's recollection. Emissions control?

Gramps

I had not thought of that, but you're right.

OK - after a little more study of the diagram that I linked, and seeing how the thermostat housing is constructed (from another figure/sketch in the FSM that I did not post), that heater return tube ports to the engine side (temperature sensing side) of the thermostat, so the heater circuit (which also feeds the pressure bottle) acts as a thermostat bypass during warmup - that's what initially opens the thermostat.

You had me going for a minute there, because without that heater circuit bypass, that thermostat might never open on warmup. That also would get the passenger compartment heat operating as quickly as possible.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

If that is really the layout, the bypass flow must come back directly across the thermostat element or it would never open.

That is not even close to what I said.

What part of "the thermostat does NOT limit the maximum temperature of the engine - it regulates the minimum temperature" do you not understand???

You are way off of the ball park - out in left field. The stat starts to open roughly 3 degrees before the rated temp, and is fully open at about 20 degrees over rated.. It us far enough open to provide appreciable coolant flow at the rated temp. IF the rad sheds enough heat from the coolant to maintain 190F ( with a 190 stat) with this opening, it will not open any farther than this - and if it sheds no more heat than is required, it will not re-close or "modulate"

The "typical" coolant system has the thermostat at the "engine outlet" or "radiator inlet". It prevents coolant flow into the rad untill the operating temp of the engine reaches the set point.. The fan control sensor is usually at the bottom of the rad - but can also be at the top., particularly on a crossflow rad, where it is on the outlet side (generally). The fan only comes on when ambient airflow through the rad is not sufficient to keep the return temp cool enough to avoid overheating the engine after the "cooling load" is pumped back into the coolant from the engine.

On many of today's engines, there is ONLY ONE COOLANT TEMP SENSOR, and it is in the water outlet or the cyl head. The computer is programmed to turn on the fan when a set max temperature is exceded. That max temp is usually significantly higher than the thermostat rating ( aprox 20 degrees IIRC)) Boiling point is somewhere above 230F

The switches on engines that use a separate fan control have hysteresis built in. As an example, one used by Ford turns the fan on at between 216 and 232, and keeps the fan running until the temp drops to 201. Another turns on between 202 ans 228, and turns off at between 198 and 218. Another turns on between 207 and 217, and turns off at 192.

One GM switch turns on between 224 and 236, and turns back off at 121.

One used on the Chevy Geo turns on between 184 and 196, and turns off at 181.

One used by Chrysler turns on at 193-207 and shuts off at 175

A 10 degree hysteresis seems to be pretty close to standard.

Nope - totally different system That sucker has a bypass thermostat. The water circulates through the block bypass untill it reaches operating temperature - then it allows a bit of cold water in from the rad. This system DOES modulate, and controls the temperature to a closer tolerance for emission control. Even worse system to install a colder thermostat in.

Yes - as I said - the heater loop return ports to the block side (sensing element side) of the thermostat. Heater loop acts as a bypass.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Heater loop is the bypass - returns to the sensing element side of the thermostat. See the diagram I posted the link to.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

In my earlier post I said: "...if the factory thermostat typically goes to full open at normal engine operation, then all the lower temp. thermostat would mean is that it opens sooner and once the engine reaches full operating temperature, there is no difference between having the 195 or 180° thermostat (i.e., engine would not operate any cooler, fans would duty cycle the same amount) - it would, however, take longer to reach normal operating temperature".

Is that not what you are saying??? (That's for the scenario in which the thermostat normaly goes to full open at normal engine operating temperature, which I though is what you are claiming).

That is one scenario that I covered. I said I did not know which to be the case for that vehicle - I covered both scenarios for discussion: Full open at normal operating temps., and a modulating thermostat, which you yourself covered in another post this afternoon (from your post: "This system DOES modulate, and controls the temperature to a closer tolerance for emission control."). We are both saying that there are both types of systems. We just need to be clear about which we are describing at any one time.

Yes - two different systems.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

OK - so this is the second type in which the thermostat would modulate (rather than running full open under most normal operating conditions), correct? In that case, the thermostat *is* in the loop of controling the engine temperature, would you agree?

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

huh. never woulda thunkit, but looks like you're right. thanks for the education. Wonder why they did it that way?

nate

More precise temperature control. With the configuration Bill posted, it looks like the fans keep the reservoir of water in the radiator BELOW the engine's optimum operating temperature, and the thermostat can blend water from a "cool" reservoir (the radiator) and a "hot" reservoir (recirculation from the engine block) to get an optimized stable engine temperature under a pretty wide range of driving conditions. The system like my '93 has probably 5-10 degrees of variability because the thermostat sets the minimum temperature and regulates it on the highway, but the electric fan control sensor regulates the temperature in traffic with the thermostat wide open.

Yes TO A POINT. That point is reached when the stat reaches full open and the cooling system can not shed all the heat. Doesn't matter if you have a 140 or a 215 stat - if the system wants to run at 235 IT WILL.

Understood (from the beginning) and agreed.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")