160 deg. T-stat

[hyracer]

Does anyone know if the 160 degree aftermarket thermostat being sold to the SRT4 modders will work in the GT? I can definetly feel the power differance when my car is below normal operating temperature, once up to temp the computer is either pulling the boost back a hair or is not running as much advance in the timing. [:I]
Deen

[Dalite]

Without changing the programming of the PCM to lower the temperature that the cooling fans come on, I can't see it having much affect in stop and go. There would have to be enough wind coming through the radiator to keep the water circulating at a lower temp, and this would seem only available at highway speeds.

I believe the programing of the computer varies greatly below the operating temp that is maintained by both the thermostat and radiator cooling fans. I don't know how this affects the a/f ratio or mileage. There is an active thread on the SRT-4 forum, and it makes some good points for and against the lower temp tstat.

If you are doing a lot of freeway driving, it should be effective. In everyday driving, I don't think it would give much help unless the PCM was programmed for the lower cut on temp of the cooling fans.

[MX-5]

The PCM won't go into closed loop until the coolant reaches 172F.
Anything less than that will waste fuel and keep the PCM from doing it's job.
Although the coolant during highway travel will be cooler, you will still heat up to 206F before the cooling fans come on. At that point, you will not see anything different in driveability. The coolant and engine will remain at 206F until highway speed cooling brings it down.

The cooling fans regulate the operating temperature during performance racing (1/4 mile drag racing).
The cooling fans are disabled above 44mph by the PCM. There is sufficient airflow to cool the engine above 44mph.

This is detailed in the service manual and powertrain diagnostic manual.

[GT_Firebreather]

You could also be noticing a drop in power after the car heats up because the intercooler is becoming heat soaked and not operating as well. This is the nature of the beast, and why Co2 spray systems (and water spray systems to a lesser extent) give hp boosts.

[hyracer]

Dalite, I've been reading the SRT4 thread with interest and my intereptation of what's being said is leaning in favor of the 160 T-stat install. It looks like a manual switch would be needed though to run the cooling fan (bypass the PCM). Maybe a 180 T-stat would be better to keep the PCM from going to the cold-start loop.

MX-5, thanks for the factory info...never knew the fans were disabled above 35 MPH. My only interest on the low temp T-stat was for drag-racing purposes. At Woodburn where I run most of the time it's at least 1 hour between heats so the car has time to cool anyway. At tracks like Madras additional cooling is needed as you may be able to make back-to-back runs in 20 minutes or less.

GT Firebreather, I've noticed the differance just driving to work (6 miles)...hardly time for the intercooler to become heat-soaked.

Thanks guys for the input!!!
Deen

[Dalite]

quote:Originally posted by hyracer

Dalite, I've been reading the SRT4 thread with interest and my intereptation of what's being said is leaning in favor of the 160 T-stat install. It looks like a manual switch would be needed though to run the cooling fan (bypass the PCM). Maybe a 180 T-stat would be better to keep the PCM from going to the cold-start loop.

Well, here is another consideration... The high and low speed fan relays were eliminated on the GT in favor of a PCM controlled fan. The diagrams look like it has a "sense" wire going to the fan from the PCM. I haven't looked any deeper, but I would guess that any change to this circuit may make the PCM mad. I would take a good look at the wiring diagrams in the 2003 Factory Service Manual and make a decision from there on the manual switch.

At least an 180 degree one would let the PCM give better control of the engine variables; especially A/F mixture.

I had made a half-hearted suggestion to TurboG to include a slightly lower t-stat in the Stage I package and re-calibrate the PCM for it.

I made this suggestion when I found out that the only way to replace the "Oring" in the t-stat housing was to buy a new thermostat.

Luckily, the one that is on the stock t-stat is fairly durable, and allows you to reuse it. However, if you don't line up the notch, or if you let it slip while negotiating the bracket obstacle on the front t-stat housing bolt - it may not seal properly.

One thing to keep in mind about the discussions on the forums. It is easy to confuse the performance of a colder engine in summer time with enhanced performance.

Unfortunately, at those temps, the thermostat has't opened. As soon as it opens, the fans will take over and maintain the temp at the stock setting. At highway temps, the fans are off, the temp may slip below the 172 degree mark, and you will have an open-loop system.

This may ultimately cause the OBDII system to do it's job and store emissions-related errors that could cause a smog-check failure (in shops that are using a scan tool to check for errors before continuing a smog test.

From what I see, it may be the wrong thing to do. A lot of folks that have much more experience than I do seem to also be against it.

I would go with the 180 if I felt compelled to experiment, and see what happens from there. Even with it in place, in traffic, below 35 MPH, the engine will still run around 215 degrees.

Let us know...

[Jabber Jaw]

quote:Originally posted by MX-5

The cooling fans regulate the operating temperature during performance racing (1/4 mile drag racing).
The cooling fans are disabled above 35mph by the PCM. There is sufficient airflow to cool the engine above 35mph.

This is detailed in the service manual and powertrain diagnostic manual.

The fans are NEVER disabled above 35mph. They are always monitor by the PCM. If temp starts raising, fans are turn on but NOT at full speed. If temp keep raising and goes up to 215F, then they will be turn on at FULL speed no matter if you are stopped or crusing beyond 35 MPH. Those manuals sometimes are wrong. If weather is hot, At 50mph you can hear them working if you have your window open.

Regards [^]

[MX-5]

OK.
Here goes.
I was partially wrong. Jabber is partially wrong.
Mopar uses 44mph as the fan disable speed, not 35mph (that's Ford)
I work on 200 different models of cars, so I get things swapped in memory sometimes.
If you hear fans running at highway speed, you are hearing the AC operation. The cooling fan operation is disabled above 44mph, except in emergency overheat situations.

As for a service manual being wrong.... I am the 4th generation in the automotive business in my family. We learned to trust in the best source of information as far back as 1909.
There can be typos. I'm the guy who got the PT service manual changed for the spark plug torque specs after the 2001 manual printed a typo.

Here's the chart from page 7-55 of the 2002 service manual.

[Jabber Jaw]

quote:Originally posted by MX-5

OK.
Here goes.
I was partially wrong. Jabber is partially wrong.
Mopar uses 44mph as the fan disable speed, not 35mph (that's Ford)
I work on 200 different models of cars, so I get things swapped in memory sometimes.
If you hear fans running at highway speed, you are hearing the AC operation. The cooling fan operation is disabled above 44mph, except in emergency overheat situations.

As for a service manual being wrong.... I am the 4th generation in the automotive business in my family. We learned to trust in the best source of information as far back as 1909.
There can be typos. I'm the guy who got the PT service manual changed for the spark plug torque specs after the 2001 manual printed a typo.

Here's the chart from page 7-55 of the 2002 service manual.

You are 100% right my friend!!! Also I was only referring to the "The emergency overheat situations." which, with raised boost, occur a lot he he he. Under normal conditions, yes, at 44 MPH the fans are disabled as those are not need it (44MPH = 70 KMH).

Saludos [|)]

[Exhaust Depot]

I think if you change it to a 160 you might have problems going in and out of the close loop. Maybe if we put a resistor on the temp sensor so it forces close loop at a lower temp then that will work.

?


OH, i have seen some type on resistor values in my toyota manual. I also work on Aircrafts and have seen mistakes on that too.