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Discussion Starter #1
Does the lower valve thermostat help reduce ST knk during MDS mode?

Is there any negatives/positives to using it instead of the 205?

thanks
tom
 

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Virginia Gentleman
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Best to keep the proper t-stat as that's what it is designed for. Also keeps proper emissions and fuel mileage. If you're having problems with spark knock, there is knock sensor that may be faulty. Best to do a proper diagnosis first. What grade fuel are you using? Have you checked for any fault codes?

My '06 Ram 1500 5.7L w/MDS has 178K miles and has never "knocked" - even with 87 octane.
 

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I wouldn't go below a 195 F thermostat and I also doubt that is the problem. Knock sensors should not allow the engine to ping. You have something else happening here that needs to be diagnosed properly. The thermostat temperature value is chosen as part of the MDS calibration.
An exhaust manifold leak can sound like spark knock. You are using the correct 5W-20 motor oil? Leaky or mis-routed plug wires can cause spark knock. Insufficient EGR (or lean mixtures) can cause spark knock.
There are some PCM flash updates, but none address spark knock directly. Any fault codes?
 

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As much as I like the 180 thermostat idea, the computer and sensors won't like it, everything is tuned to function at a given temp and may even throw codes if the engine cannot warm up to calibrated temps. Don't feel bad, I read several years ago the operating temp for a Corvette was in the 235degree range, totally rediculous. And for added, a carb'd engine is a totally different story, 160-165degree thermostat goes on my list of temps.
 

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Discussion Starter #5
This is not audible knk but shows up on the DS Trinty display. I run 93 oct and dino 5w-20 oil, no fault codes present. Truck has 12k miles on it so I don't think there is a plug/wire issue.
 

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Virginia Gentleman
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93 octane is not recommended. As I recall 89 octane is the recommended fuel grade for the Hemi. 87 octane is "acceptable".

What do you mean by "ST knk"?
 

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Discussion Starter #8
ST knk is short term knock.

The DS Trinty has several different tunes, I'm running the 91 oct w/93 oct fuel. The 1st time I went out on a trip with this truck running 89 oct fuel and no mods, on cruise control. 1st big hill on the interstate it did a double downshift to hold set cruise speed at 70 mph. This happen several times on two different trips. Once I switched to 93 oct that all went away.
 

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Discussion Starter #10
This device plugs into the port under the dash and can overwrite factory software, you can return to stock. You can also get a custom tune on a dyno if you want or emailed to you for a price. From want I've seen and read on aftermarket forums the 5.7L does knock easily. My high end hearing is bad so I can't hear it but the device I'm monitoring with uses the factory knock sensor and shows that output real time, just like a DRB would. This knock shows when the computer transition from MDS to normal operation. You can say your motor don't knock cause you can't hear any but without a real time monitoring device you really don't know.
 

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Virginia Gentleman
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What year is your vehicle? I have a 2006 Ram 1500 QC SB 4x2 with the 5.7L Hemi, 545RFE transmission and 3.55 gears and unless I have a heavy load it's rare for the transmission to downshift on long hills at interstate speeds (65-70 mph). I don't have an aftermarket device such that you have so I have to depend on my "ears" to hear any "knocking". Though I will say the DS Trinity does sound sort of neat with real time monitoring.

The most common problem with regards to the 5.7L Hemi I've read on other forums is the infamous Hemi "tick". Some have it, some don't.

Is the knock just during the transition from MDS to normal operation (all 8 cylinders) or does it continue to "knock" in full V8 mode? If it's short term, it may just be the nature of the beast.

Agree with Dave in that it could have been mislabeled or bad fuel. I haven't had any "fuel" issues, but do know a friend who's Tahoe runs poorly if fed anything other than Exxon fuel. Or so she claims.
 

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Discussion Starter #12
Doug D said:
What year is your vehicle? 2011 I have a 2006 Ram 1500 QC SB 4x2 with the 5.7L Hemi, 545RFE transmission and 3.55 gears and unless I have a heavy load it's rare for the transmission to downshift on long hills at interstate speeds (65-70 mph). I don't have an aftermarket device such that you have so I have to depend on my "ears" to hear any "knocking". Though I will say the DS Trinity does sound sort of neat with real time monitoring. All PCM outputs on the bus can be converted to a gauge to watch, 4 at a time, after that it's too small to see.

The most common problem with regards to the 5.7L Hemi I've read on other forums is the infamous Hemi "tick". Cold start Some have it, some don't.

Is the knock just during the transition from MDS to normal operation (all 8 cylinders) or does it continue to "knock" in full V8 mode? Yes and no knock in V8 mode If it's short term, it may just be the nature of the beast.

Agree with Dave in that it could have been mislabeled or bad fuel. I haven't had any "fuel" issues, but do know a friend who's Tahoe runs poorly if fed anything other than Exxon fuel. Or so she claims.
 
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