knocks when cold
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knocks when cold
I have a 98 F150 with 5.4 litre engine that knocks when cold. It seem to do this when giving it somegas under normal aceleration When aceleratingharder the knock gets louder. Onceengine is warmed up can't hear the knock any more. Theoil is topped to the proper amt by the way.
Any ideas what is causing this?
Thanks Chip
Any ideas what is causing this?
Thanks Chip
Senior User
Joined: Aug 2003
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From: Eastern, Iowa
My Navigator does this as well. Scares the hell out of me because I was thinking a rod was knocking (112K miles). Nice to see others having the same thing happening without the bottom-end falling out! Can't wait to see the replies
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Joined: Aug 2002
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From: BC, Canada
Hi Chip and welcome to FTE 
Piston slap is somewhat common on these engines and Ford says it wont do any damage and not to worry about it. Basically when the engine is cold the pistons sort of shrink and go out of shape and will rock in the cylinder bores which makes the noise. As they warm up they expand and return to the proper shape and the noise goes away.
Another thing that can make a similar noise is an exhaust leak. It usually sounds more like a loud tick than a knock though. The most common cause of that is broken studs that hold the exhaust manifolds to the heads, usually on the passenger's side of the engine. Again once it warms up and everything expands the noise goes away.
Piston slap is somewhat common on these engines and Ford says it wont do any damage and not to worry about it. Basically when the engine is cold the pistons sort of shrink and go out of shape and will rock in the cylinder bores which makes the noise. As they warm up they expand and return to the proper shape and the noise goes away.
Another thing that can make a similar noise is an exhaust leak. It usually sounds more like a loud tick than a knock though. The most common cause of that is broken studs that hold the exhaust manifolds to the heads, usually on the passenger's side of the engine. Again once it warms up and everything expands the noise goes away.
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My truck which has 112,000 miles had the exhaust studs replaced last year, which took care of the ticking on the passenger side, which is quite common . As for the knock, I'm just driving it and hoping for best, It's loud at 0 degrees Farh. , but goes away when warm.
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I also have a knock in my 'cold' 5.4 engine in a 2000 expedition. I have 78K miles on the engine. I am planning a trip to northern Alaska this July and I am wondering if I can expect engine problems due to the knock. Appreciate any feedback. tks..
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There are many posts about this problem. Mine has been doing it for quite afew thousand miles, haven't heard of anyone' blowing an engine though. Piston slap , what it's prob. called, is quite common on these engines. As long as it goes away after warmed up your OK. Have a good trip to Alaska.
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I'm curious. Can anyone explain why some engines experience this problem while others do not? It seems that with the engineering and manufacturing standards that exist today there would be a problem with all 5.4 engines and yet that apparently is not the case. Also, I had a '96 Mercury with a 4.6 engine and did not experience this problem. Just puzzled !!!
Senior User
Joined: Sep 2003
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From: Valparaiso, Indiana
my motor experiences that knocking sound that everyone is describing as well...it's the worst when it's cold of course but fades out when it warms up...but it doesn't fade out complete and you can always still hear it even when fully warmed up...85k miles at the moment...i run castrol syntec 5w30 oil
More Turbo
Joined: Dec 2003
Posts: 660
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From: Southeast Kansas
My 2001, and my 2002 trucks both have the "knocking sounds" that you are describing. So, the other day, when in for a oil change, at the Ford dealers, I ask te service writer about it. He says: "It is normal, and the way the engine is designed". "Because the oil has to come up from the oil pan, filter, etc., to get to the top of the engine". I'm not a mechanic, that's just what I was told.
