Loud clank sound at sub-freezing start-up

[calskibum]

Over the weekend, I took my LC to the snow country. This was the first time that my LC was parked outside where overnight temp was in the single digit. When I started it up in the morning when the temp was still in the teens, I heard a single loud clank coming from under the hood just a fraction of a second after the engine turned over. This loud clank sound happened two mornings in a row, but otherwise the LC appeared to be normal. Now that I am back to the above freezing temp, the clank sound did not happen again.

During my search on the forum, I read that people mentioning their LCs make all kinds of different weird sounds during start-up in sub-freezing temp, but I didn't read one that sounded like what I heard.

Has anyone experienced this in freezing weather or knows what caused the sound, and If so is it something that I should worry about?

 

[KLF]

Fan clutch releasing? Just a guess.

 

[calskibum]

I'm not very familiar with how the fan clutch works. Does it mean that my fan clutch might be on it's way to failing or is it just prone to making the loud sounds in freezing weather?

 

[Nottajeep]

Starting mine recently in sub zero F temps, it did all kinds weird stuff.
Cut off after starting, loud noises when starting, lethargic cranking, threw an APS code, etc.. and I have all PM's done and premium fluids with a new battery.

Sent from my droid

 

[George 2000]

I'm sure this has been discussed somewhere on here, but the 4.7L motors have had an issue with dissimilar metals in the engine block expanding at different rates on cold start-ups. Basically, it's a tolerance issue which I believe has been defined as "piston slap." If it's like mine, it goes away a few seconds after start, and only occurs on start ups after cold nights. The consensus seems to be that it does not cause any undue ware on internal engine parts.

 

[calskibum]

The sound that I heard was just one loud clank a fraction of a second after the engine turned over. This happened two separate mornings in similar temperature. It almost sounded like two metal pipes banged against each other or something metallic snapped in half. Is this the piston slap that was mentioned?

 

[APKhaos]

No, the piston slap noise is dull thunk repetitive with engine revs. Its typically fairly quiet, and more likely to be heard from outside than in the cabin. The noise you describe sounds a lot more dramatic.

 

[calskibum]

Thanks for the clarification. I'm headed to the snow again early next month and I'll see if the LC makes the same sound again on sub-freezing cold start.