Its been pretty cold here in Memphis the last few days and i've noticed that my engine has a knock/diesel sound until it is completely warmed up. runs fine though. what is causing that and is it a big deal? anybody else have that happen? was also wondering what kind of rpms i could expect to turn pulling about 4,000lb--does it wind it up pretty good through all the gears? '06 STX 4.2, 3.55, automatic with 5K. thanks.

 

What weight oil are you running and when was the last oil change. to heavy an oil or weak pump. what is your oil pressure at idle when cold and when hot?

 

In OD cruising down the freeway, it's about 30 RPM per MPH.
So, 70 MPH X 30 RPM = approx 2,000 RPM.
The load makes no difference. It's all a matter of vehicle speed and what gear you are in.

 

using the recommended 5w-20 motorcraft synthetic. just changed it over thanksgiving. brian, did you calculate that specific to the info. i gave you or is that standard? just seems weird that i can run empty at 70 turning 2,000, which is dead on, by the way, and do the exact same thing pulling 4,000lbs. seems like the motor would be working a lot harder than that. i'm probably exposing myself as an idiot here...thanks for the responses.

 

I used the Odometer set to test mode and then set to the Tach mode to read RPM while riding down the hiway. Pretty simple math told me it as about 30 RPM / MPH in OD.
As far as the engine working harder and that relating to RPM, there is no relationship at all.
And no you aren't looking liek an idiot.
A reasonable question to ask if you don't understand.
How else will you get a clear picture if you don't ask a question?

Think about riding a bike. You pedal down the road at 10 mph.
Somebody comes along and jumps from the back of a truck and lands on your back (ouch).
In order to maintain 10 mph, you just have to work (pedal) HARDER, not pedal FASTER.
If you pedaled faster, you'd go faster.
Same exact thing in your truck.

The engine/transmission = you/pedals and front sprocket.

The only way the vehicle will go faster is if the "engine" goes faster.

Make any sense?

 

There is no such thing as a dumb question. Only dumb answers

 

yeah, think i got it. thanks. any ideas on this cold engine knock? sounds just like a diesel idling but i cant hear it when i'm driving. goes away completely when the engine is fully warmed up. drives fine though.

 

Some guys have reported a noisy oil pump. Makes a loud ticking sound that I guess could sound like a diesel engine.
Try getting a mechanic's stethascope and use it to try and isolate the source of the noise.