In my 2012, the rattling or more like a clanging tin sound coming from under the engine at idle was only a couple of aluminum plates butted up at a 90 degree right under the transmission (where it connects to the engine). With the engine on, I located the source of the sound by laying down on the passenger side under the truck. Right where the transmission sits and attaches to the engine, there are some aluminum covers over some wires. My guess is these are heat shields from the exhaust. Where the plates touch each other is where they start making that sound, like jingle bells, or an iritating marble in tin cans sound. I pushed down on one and gave it a little pressure, and it went away. So, I just bend it out just a little, so that it doesn't touch the other plate. Sound is gone.

Side question, I'm running 87 in my truck with no problems. Will the MDI have a problem in the summer if I ran 10w30 oil. I'm just wondering if that oil would be better in the AZ heat. 5w20 seems too thin for 110+ heat. What do you think?

 

Use the recommended oil. So far after 4 summers in AZ the hemi using 5w20 is doing just fine. I would not use 10w30 (personal opinion).

 

Not hotter where you are then many other places. Don't out guess[ the design. I've only run 87 a couple times. More by accident. I use the preferred fuel. The 2012 5.0 Mustang is advertised with TWO h.p. ratings. 87 and 91 plus fuel. There is a 18/19 horse difference from 87 to 91 plus. Bet the Hemi has 'difference'. Maybe not that much but still there7 is a reason 89 is the 'preferred octane'

 

I will make sure to stick with the recommended oil and will switch to 89. I am at 4000 miles with only 87 octane. I'm not sure what 87 will do; I'll have to do more research. I used to haul fuel and I blended 91 and 87 to get 89. Thanks for your answers

 

The engine won't like the 10w30 much, stick with the 5w20. As for the octane - I've run 87 and 89, never noticed a difference between the 2 in terms of mileage and there is no way I'd notice an HP difference (its a truck and it is used as such). 89 is the same price as 87 at the local Holiday stations so I use mostly 89 now.

 

Thanks OldJeep. That makes sense. I looked at octane and there are claims that if you are using lower than the recommended octane, the engine may start knocking due to pre-ignition. High compression engines should use the recommended fuel, they say, but then qualify that most engines have sensors that prevent pre-ignition. If there is no difference in price, then it doesn't matter, like you said; especially if you don't have knocking.

http://www.exxon.com/USA-English/GFM...y_gas_faq.aspx

 

It won't 'knock' unless it can't retard the timing far enough to compensate a to low a octane fuel. It retards the timing! To prevent knock. I can feel a difference in 87/89. Its not as 'sharp' feeling or crisp on 87. If you want to run 87 do so. They say it won't kill it. But there is a reason they say 89 preferred. They didn't say preferred it for the hell of it.

 

page 386 of the owners manual

The 5.7L engine is designed to meet all emissions regulations and provide satisfactory fuel economy and performance when using high quality unleaded gasoline having an octane range of 87 to 89. The manufacturer recommends the use of 89 octane for optimum performance. The use of premium gasoline is not recommended, as it will not provide any benefit over regular gasoline in these engines.

 

anyone know how many exhaust bolts there are on the 5.7s?
looks like I'm going to need mine replace again (first was March 2010). They replaced 9 the first time according to the invoice.

 

Looks like 8 per side according to the FSM