Thread background 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. Here is a compilation of many discussions across several boards on the subject. You will notice several pictures are actually of my previous MSRT8, but the information applies just the same. Where to buy and how to get what you want There is a definite concensus that the Motorad (a.k.a. Valuecraft) family of bypass t-stats are the best choice for upgrading the 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 are readily available and in stock at any AutoZone. In fact, you can now 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. 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. This is why a 180-degree t-stat is the most popular for daily drivers. 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. 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 7720. It is rated at 20# versus the stock 18#. It also features a safety pressure relief lever. Replacement Instructions 1. MAKE SURE ENGINE IS COOL!!!! 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.
No problem. This is essentially a copy of a similar post on another site. I reposted it here by request. I hope it helps. Let me know if anything is unclear, and I will do my best clarify. Regards,
Many thanks go out to Meister - as his thread (on another site) provided much of the technical content here.
Very very nice. Any suggestions on how one would go about removing the extra 0.5mm? Can you chuck it in a drill to spin it against a file or sand paper?
Oh, yea. Does everyone experience radiator cap spitting after this? My radiator cap seemed to be spitting when I took it in for the coolant RRT. I'm not sure if replacing the cap was a separate issue or TSB. Somehow I got the impression it was.
I would recommend a bit of hand grinding on a table grinder. Just make sure you are using a smooth, less-aggressive stone. 0.25mm is a VERY small amount.
A fine, flat metal file (not a rat tail) would be my choice - sandpaper is unlikely to do the job. Emery cloth might work though.
Thanks for posting this over here, it was me that asked him to do it as it is a VERY detailed and thorough write up even I can do it now just the whole shaving down the t-stat has me a little worried
Just got mine today...and will be doing this on Sunday. One question...how big is the bypass hole in the housing when compared to the lower flange on the stat? Thanks, Keith
I found time to get mine put in tonight...it runs between 181 and 183 running down the highway. I get my Predator tomorrow so I can adjust the fans accordingly. Keith
I FINALLY did the T-Stat mod at JMatt's house last weekend when I went to go racing. They didn't have a single 4128 at ANY Vatozone in Illinois so I picked one up near his house. I gotta say that little mod (coupled with my predator) made my car one of the most consistent bracket racing cars I've ever seen. It attribute it all to the T-Stat. My temps at the line were always 185 (what I set the predator to always keep them at) It was very hot that day: 1st run = 13.359 2nd run = 13.357 3rd run = 13.355 Yes folks, that's 3 runs within 4 thousandths of each other!!! My 60 foots on the first two runs were IDENTICAL @ 2.082!!!!!!! I've raced my car a bunch of times and I've always varied by .25-1.00 full second! That is a testament to how much heat variation can make our cars inconsistent and how much this simple mod helps. I will say that the track was prepped very well so I didn't get any wheelspin. I love the T-Stat mod!
thermostat replacement - another hint To catch the coolant, insteasd of a freezer bag try an empty 1/2 gallon cardboard/paper orange juice container. Car must be COLD and radiator cap tight on overflow tank befor cooldown starts. Cut the oj contianer about half way down in height, leaving one side a little longer with a curve cut to fit underneith the t-stat boss on the engine. Container is flexible and you can fit it under stat housing and upper hose, it will stand on the belt tensioner. Hold it up under stat boss and remove bolts, (leave hose clamped to housing) allowing hose to drain into container. Now, EMPTY the oj container into a larger vessel and replace before removing stat - taking stat out will fill container again. The only coolant I lost was an once or so that dribbled from the bleed hole on top of the stat. This is easy for one person to do.