Basically, a great truth to making power is "HEAT IS BAD". Any way you can rid your engine of the heat it produces will yield more power for a longer period. Lowering your thermostat's opening threshold via replacement with a lower-than-stock unit can help. Thermostat replacement is a BIG subject among all SRT8 model owners including all makes (Jeep, Chrysler, and Dodge). Much discussion regarding the various types and manufacturers has been hashed out. I've noticed several discussions on this site, but none that collected the information into a single, readily available post. Therefore, I decided to compile the most important information and slap on a pictorial "how-to". Maybe, it will help some of you who are sitting on the fence trying to decide what to do. I know I had similar questions the first time I performed this mod.
Where to buy and how to get what you want
There is a definite concensus that the Motorad (a.k.a. Valuecraft, Duralast) family of bypass
t-stats are the best choice for upgrading the 5.7L and 6.1L HEMI. These products are solidly built, have a fail-safe feature (ensures full open position in the event of failure), and fit our motor. The Motorad 4127 (170 degree) and the 4128 (180 degree) are readily available and in stock at any AutoZone. In fact, you can order them online
. Taking this "shopping list" to your preferred AutoZone ensures the monkey behind the counter does not argue with you and insist on looking up your vehicle. It will not
pop up this way. If you just show up, then insist on a cross-reference search using "4127" or "4128" as the search criteria. Pick the only t-stat that shows up on the results. EDIT: Others are running the Jet 10183 (180-degree) t-stat
. The pictures online show a non-bypass model, so I can't vouch for it. The claim here is a better fit with similar quality.
Why is a "bypass" thermostat important?
Bypass t-stats are a must for the long-term health of your motor. The pic below shows a bypass t-stat next to a non-bypass unit. Since the 5.7 and 6.1 HEMI motors use a bypass cooling system, a traditional non-bypass unit will allow hot coolant to bypass the radiator once the engine warms up. This can cause engine damage in the long run. For more information on this subject, please refer to this thread: http://www.are.com.au/feat/techt/thermostat.htm
Things to consider
1. Depending on your driving habits, a 170-degree t-stat may trigger a code due to the motor not warming to above 175 or so. The code will not cause any immediate problems; however, a minimum temperature threshold is set in the PCM for emissions compliance and to ensure flash-off of any moisture in the motor. Moisture can cause pitting of the metal among other things if left for very long periods. This is why a 180-degree t-stat is the most popular for daily drivers - the chance of throwing a code is greatly reduced.
2. The MotoRad t-stat is actually 0.5mm larger in diameter than the stocker. There has been a concern raised regarding the damage this may cause the rubber gasket. Although, I do not personally share this concern, you may be interested in shaving 0.25mm off the Motorad's metal flange to ensure an exact OEM fitment.
3. There are several who have experienced coolant leaks around the stock radiator cap after doing this mod - me included. You'll have to ask someone else why this is, because I don't know for sure. However, for $15 or so, you can also upgrade the radiator cap to a MotoRad 7718. It is a higher quality unit, and it is rated at 18# just like the stocker. It also features a safety pressure relief lever.
1. Start with a cool engine!!!!
Remove the air intake tube. Set aside.
2. Grab a 1/2" socket and remove the two bolts holding the bell housing and nipple.
3. Make sure you have a 1-gallon heavy-duty freezer bag to catch spillage as the bolts come out. Don't worry if you have a spill though, because there is plenty extra in the overflow reservoir to tolerate spilling most, if not all of it. NOTE:
Coolant is toxic to all animals including dogs, cats, and humans. Be sure to clean up spills promptly and thoroughly.
4. Once you drain the coolant in the upper hose, push it aside to expose the OEM t-stat and red rubber gasket.
5. Use a medium flat screwdriver to gently pry the old unit out. Be careful to preserve the gasket. Also, be ready for a final gush a coolant from behind.
6. If you intend to grind the t-stat's metal flange down to 63mm exactly, then now is the time to do it. Next, transfer the rubber gasket to the new t-stat. Install the new t-stat taking care to orient the dog bone air bleeder to the top.
7. An unground Motorad t-stat is a tight fit, so a knife or thin screwdriver can help "shoe-horn" the gasket. Once the gasket is started, push with even pressure until the t-stat seats into the housing - it will not be flush and a little gasket will protrude beyond the machined face. This ensures a watertight seal.
8. Reverse the steps above, then pour the recovered coolant back into the overflow tank. Start the engine and let it warm up thoroughly. Rev the engine a few times to help dislodge any residual air. Note the reservoir level and add more coolant as needed.
credit: Meister (LXForums) for much of the technical data