Metallic rattle in engine when starting

rowleyd said:

I have a 2003 Mustang GT 4.6 that is well maintained with 43,000 miles with great oil pressure. Recently when it is a warm day and the car has set all day when I go to start it there is an initial metallic rattling in the engine. It almost sounds like loose rods. After the initial start the sound last for a second or two then goes away at all rpm ranges. Any ideas on what it could be? I do use the recommended 5/20 oil.
Why would it only do it on a warm day and after sitting for hours?

Click to expand...

Chances are the oil isn't getting to the rods/bearings/pistons fast enough so for that split second parts are unlubricated, causing that rattle you hear. You can do a quick compression check to make sure all cylinders are getting efficient compression. If the numbers are consistant and within range, I wouldn't worry about the noise. Especially if your oil pressure is around 20-30psi at warm idle. I would worry if cruising/warm idle pressure is below 20psi. but the compression test is most important.

Also another thought: The noise you are could be detonation from crappy gas or the wrong octane. Try different gas stations and different octane ratings. Some stangs run perfect with 87 oct while some stangs need 89oct. Even if you are running stock timing.

What type of oil filter do you have? If it's a Fram, take it off and put a Motorcraft one on.