Should I replace my OEM thermostat?

For thermostat write-up: https://rivperformance.editboard.com/t3484p15-write-up-thermostat-installation#41776


Replace the thermostat? For supercharged engines, the short answer is yes.

Changing the stock thermostat to a 180ºF unit will slightly lower the engine block temperatures by opening sooner (at a lower temperature). This helps to fight spark knock, which enables the engine to generate more power. A 180º unit will not interfere with the ability to heat the car in winter. 180º units can be purchased through most auto parts stores, or at any of the online 3800 V-6 vendors for around $5-10.

160ºF thermostats are also available, but understand that there are issues related to the engine running too cool that make the 160º unit undesirable in most daily driving situations, especially in cooler weather. For racing purposes, or in very hot climates, it may make more sense.

Results of installing an aftermarket thermostat in '98 Riviera

One concern when modding the L67 is how to rid the combustion chambers of excess heat. The easiest way to help lower engine block temps is to install a thermostat that opens at a lower temperature and flows more coolant than the stock unit.

Here is a graph showing two separate scans of my car, one with the stock thermostat and another with an INTENSE high-flow 160ºF unit installed. The tests were done on a 40ºF day over a span of less than 10 minutes, most of the time cruising at 65mph:



As you can see, the aftermarket 160º t-stat does its job quite well. After opening at 155ºF, the unit lets temps fall to as low as 140ºF, and it stays open after the engine completely warms up, keeping the engine at a sustained 145ºF operating temp at freeway speeds on a cool day. Note that 145º is much too cold for practical daily driving, and the 160º unit was removed after this test. But it shows its effectiveness.

In contrast, the factory (195º) unit lets the engine heat up to ~200ºF and then allows temps to fluctuate up and down within a tight 10 degree window as it opens and closes about once per minute. As far as I can tell, it does this continuously at freeway speeds, especially in colder weather.

Not exactly a ground-breaking study, but it's interesting to see how each t-stat operates. The end result is a considerable lowering of engine temps - an average of 50 degrees - a bit more than I had expected.

Caution: it has been determined that using a 160º t-stat can be dangerous for our engines in colder weather. The Riviera's PCM comes programmed with a setting called "KR activation temp". This setting is a specific engine coolant temperature value (158ºF), above which the engine's knock sensors will be activated and "listening for knock". Below this point, the sensors are ignored by the PCM, and the engine will likely knock (audibly) if pushed to WOT. For this reason, it would be unwise to run a 160º unit in ambient temps much cooler than 65ºF, as engine coolant temps will drop below the KR activation threshold.

Through the use of a PCM programmer like the DHP PowrTuner software, the KR activation temp can be set to a lower value (-40ºF) so that the knock sensors are "listening" at all times. However, it is suspected that running with an engine's coolant temps much lower than 180ºF can cause excessive engine wear over time, so it may not be a good idea to run a 160º except for racing applications. On the other hand, there are those who feel running cold is of not as much concern. Run the 160º t-stat at your own risk. A 180º unit is safer choice until it is known for sure how badly our engines wear at lower temperatures.

After this test, it was decided to use a 180ºF thermostat for the best balance of cooling performance, knock reduction, fuel economy, interior heating, and engine longevity.

I thought I saw somewhere some modular type system or something. I don;t know, all I remember is you could change the temp yourself via a wired digital remote/display unit

why would you want to? for that +1 mpg fuel econ
i really didnt see any drop in fuel when i switched to the 180*

No, it was in order to change the temp on the fly. So if you are driving around town you could keep it around 180* or whatever you want, then at the racetrack it could be easily set to 160*. Then when you are done back to 180*

i just put in a new radiator today and a 180* thermostat. the thermostat opened at a/b 185 but the fans did not come on until a/b 210 does anyone no why does it have to do with the computer or something.??

robertwolf86 wrote:

i just put in a new radiator today and a 180* thermostat. the thermostat opened at a/b 185 but the fans did not come on until a/b 210 does anyone no why does it have to do with the computer or something.??

Yes that is what they are programmed to do.

See: https://rivperformance.editboard.com/Supercharged-3800-Tech-c2/Series-II-Engine-Transmission-f4/Engine-temp-t413-0.htm

Tired of watching my gauge sit a little over 200. Just picked up a 180 T-stat.

That will help when the car is moving, but sitting in traffic you will still see climbing temps, unless you have modified fan turn-on settings.

1998 Riv wrote:

That will help when the car is moving, but sitting in traffic you will still see climbing temps, unless you have modified fan turn-on settings.

Taking a long trip to TN tomorrow and I am hoping for slightly lower temps. Gonna have to research the fan settings.

It will certainly help on the hwy. What year is your Riv? That will determine if you'll be able to modify the fan settings. Please take some time and add basic car info to your default sig in the Profile section.

1998 Riv wrote:

It will certainly help on the hwy. What year is your Riv? That will determine if you'll be able to modify the fan settings. Please take some time and add basic car info to your default sig in the Profile section.

I'll do that now. It's a 97 SC. The T-stat replacement was amazingly easy.

Im not driving the Rivi in the winter time at all, i have a heated storage facility i used to work at to keep the car there for the winter, i know that a 180 stats is better for cooling, so 160 has to even better right, if im only driving the Riv in the warmer months, is the 160 a better idea?

also, i noticed when i baught the car that coolant overflow tank is full of a brownish colored liquid im imaginig is that DEX-COOL Crap, or some mixture of coolant and stop leak mabey, anyone else ever experience this?
i syphoned it out and put new coolant in but its back, im hoping its not pulling oil from somewhere through the system, im hoping that a radiator flush will do the trick. Any Ideas?????

Scroll up to 2nd post from top.

THX

So I ran into A guy At Napa Who had a 96 sc riviera and he had a 160 thermostat, Could I do that or is that a bad idea,

Ive heard that a 160 stat may cause your engine to run too cool. i think it is best for race applications only.

if i were u i would stay with the 180 i herd the 160 isn't that good on your car unless u have major mods and tuning. u put autolight 104 spark plugs in it yet?

1wickedninja wrote:

if i were u i would stay with the 180 i herd the 160 isn't that good on your car unless u have major mods and tuning. u put autolight 104 spark plugs in it yet?

me?

Read page one of this thread about 160º t-stats.

Use a 180 for a street driven DD.

i live in northern minnesota. i wanna run a 160 or 180 thermostat but dad says i will have no heat during the cold 9 months up here... i think i'll still get plenty heat...any input..thanks

The lowest you would want to go is 180* and that's only if your PCM has been reprogrammed for that temp.

A 180 is just fine up here in winter, I'm in ND. Had no heating issues last winter with a 180. DO NOT run a 160 in a daily driver.

180 is even fine up here in CANADA!