Engine Compartment Knocking when Temp is below freezing?

[RAM#2]

A few weeks ago I noticed a knocking coming from the engine compartment during an COLD morning - below freezing. Initially the knock only showed when the truck reached 55ish MPH and would go away at approx 65 MPH. Over the last few weeks the knocking occurs at lower speeds and stays around much longer but only when the outside temp is below freezing. I have found nothing loose in the engine compartment, under the truck, or...... The knock only occurs when going down the road and does not have any set rhythm - I can put the truck in Neutral while coasting and the knocking goes away. Any Clues????

 

[bigdodge]

A few weeks ago I noticed a knocking coming from the engine compartment during an COLD morning - below freezing. Initially the knock only showed when the truck reached 55ish MPH and would go away at approx 65 MPH. Over the last few weeks the knocking occurs at lower speeds and stays around much longer but only when the outside temp is below freezing. I have found nothing loose in the engine compartment, under the truck, or...... The knock only occurs when going down the road and does not have any set rhythm - I can put the truck in Neutral while coasting and the knocking goes away. Any Clues????

what octane gas are you running?

 

[NRitland2]

Do you let it idle/warm before driving it when its that cold?

 

[RAM#2]

what octane gas are you running?

87

 

[RAM#2]

Do you let it idle/warm before driving it when its that cold?

Sometimes - no change to symptoms.

 

[bigdodge]

87

try 89 or higher

 

[ferraiolo1]

87

It’s recommended tow run 89 in these trucks. To eliminate pinging.


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[OldMarine]

the 89 octane recommendation is actually to get "peak power" out of the engine, and running 87 should not cause any pinging,(detonation). The engine management computer would adjust timing if needed. Even the maual says it's ok to run 87.

 

[theblet]

Maybe exhaust manifold cracks? It may go away as the metal heats up and expands.

 

[ferraiolo1]

the 89 octane recommendation is actually to get "peak power" out of the engine, and running 87 should not cause any pinging,(detonation). The engine management computer would adjust timing if needed. Even the maual says it's ok to run 87.

The truck can only pull so much timing, and it will still ping with 87 under certain scenarios. There is a massive thread about this already.

If it was a cracked manifold it would do it at idle, and not so much while driving. And wouldn’t go away in N


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[Ramjack]

If this had anything to do with fuel octane, why would the OP's truck make the noise only when it is cold outside? Colder ambient temperatures reduce the tendency of a gas engine to detonate. In cases where a particular vehicle is known to exhibit detonation more during the winter vs summer, it is because of the higher volatility of winter blend fuel. In the OP's situation, he has winter blend fuel whether the temperature is below freezing or warmer.

Question for OP: You say the noise goes away when you put the truck in neutral while coasting down the highway. What happens if you leave the truck in drive while coasting (foot off the gas)? If you're hearing the noise while coasting in drive but NOT while coasting in neutral, the sound has nothing to do with the engine.

 

[ferraiolo1]

Just a variable that’s easy to eliminate. Plus winter blend fuel is known to perform worse.


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[OldMarine]

The truck can only pull so much timing, and it will still ping with 87 under certain scenarios. There is a massive thread about this already.

If it was a cracked manifold it would do it at idle, and not so much while driving. And wouldn’t go away in N


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sorry, disagree. I pulled #6500 worth of cargo and Travel Trailer 2000 miles last year on a trip running 87 all the way. No pinging EVER. Again, the manual says it's ok to run 87.

 

[RAM#2]

If this had anything to do with fuel octane, why would the OP's truck make the noise only when it is cold outside? Colder ambient temperatures reduce the tendency of a gas engine to detonate. In cases where a particular vehicle is known to exhibit detonation more during the winter vs summer, it is because of the higher volatility of winter blend fuel. In the OP's situation, he has winter blend fuel whether the temperature is below freezing or warmer.

Question for OP: You say the noise goes away when you put the truck in neutral while coasting down the highway. What happens if you leave the truck in drive while coasting (foot off the gas)? If you're hearing the noise while coasting in drive but NOT while coasting in neutral, the sound has nothing to do with the engine.

The knocking will go away as the speed reduces. Don't believe it to be the engine. I originally thought it to be the water pump but I have ruled it out based upon mine and your thoughts above - coasting in neutral & letting my foot off the peddle.

 

[RAM#2]

UPDATE - Today the temps ranged from high 30's to the high 60's - Zero knocking. I took a look at the auto air dam thinking that it may be the culprit but it looked OK - I didn't see anything loose on it or.....

 

[bigdodge]

The knocking will go away as the speed reduces. Don't believe it to be the engine. I originally thought it to be the water pump but I have ruled it out based upon mine and your thoughts above - coasting in neutral & letting my foot off the peddle.

find a place with a dynamometer
have them run it at the speeds you hear the sound