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post #1 of 10 (permalink) Old 06-29-2004, 11:44 AM Thread Starter
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Rattle After Start Up (I searched)

Hey guys, I'm getting that annoying 3 second engine rattle/knocking when starting the '94 Tbird. I only use Motorcraft oil filters and good quality dino oil. It doesn't happen all the time, but when it does, it sounds bad. I checked the whole front of the motor for anything loose and its all tight. Motor has about 80k on it. Also, when I start the car for the first time after changing the oil, it does a longer version of this rattle but not as loud. Oil pressure is always normal and the car runs great. Is the oil pump having problems or whats going on? Thanks for you input.

1989 Chevrolet Caprice 5.0L 75k
1994 Ford Thunderbird 4.6L 85k
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post #2 of 10 (permalink) Old 06-29-2004, 11:58 AM
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FWIW: A friend of mine has suggested lifters as the culprit when he heard that on my car in the winter time. He suggested using a thinner oil for a while since the oil passages were a little restricted...it worked for me. I observed similar symptoms for a while, including after oil changes, just as you did. Do you use 10w30 or 5w30 in your car?

Gunk makes an additive called Valve Medic (click for product info) that's supposed to target the lifters (it's a "pour it in, and start driving right away" additive). The only thing I couldn't discern was if the oil required changing afterwards, or if it was left in. Seafoam can be used as well: the product page. People on this site who've used Seafoam in the oil have stated they perform an oil change afterwards.
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post #3 of 10 (permalink) Old 06-29-2004, 12:05 PM
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Just so you know (if you don't already), you oil pressure gauge is an idiot light. It doesn't use a real sending unit (unless you've converted it), but rather just an open/closed set of contacts. They close at I think 7 psi and take the guage needle to halfway.

As far as the rattle, I'm going to guess that one of your tensioner's clips and or springs have gone bad. There is a ratchet mechanism that holds the plunger out with no oil pressure so you don’t get that cold rattle. I’m going to assume the noise is coming from the front of the engine, and isn’t a lifter “tap”, or piston “slap”.

Without hearing the noise, it’s kind of hard to diagnose, but those are my guesses.

Hopefully someone else will chime in also.

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post #4 of 10 (permalink) Old 06-29-2004, 12:10 PM
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Maybe worn main/rod bearings if it has high miles or has had lack of maint. w/ a previous owner. My old 302 started to do that around 250K, and I had a real analog oil pressure guage running on it, and it would idle at about 7 psi at full hot, yet the idiot light would never come on. But the 4.6 is a bit different, so not sure. Just a thought. Hope it's not the Ford death rattle....

These are highly engineered precision vehicles, the first step in diagnosing the problem is to strike the suspected offending part sharply and repeatedly with a blunt object, then re-test.
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post #5 of 10 (permalink) Old 06-29-2004, 03:16 PM Thread Starter
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The only time I used to hear it was when i changed the oil. Right after using 5w30 for last winter, it started doing it on regular startups. I have just recently changed back to 10w30 for the summer. I know its not lifters or bearings or anything. It has to do with oil pressure since its only on startup and its not lifters. I will soon record it for you guys to hear. I think its the same rattle as some other guys are getting, but mine isn't oil filter related.

1989 Chevrolet Caprice 5.0L 75k
1994 Ford Thunderbird 4.6L 85k
Mods:Air Silencer Removed.
1996 Chevrolet Caprice 9C1 5.7L 130k
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post #6 of 10 (permalink) Old 06-29-2004, 04:43 PM
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Kind of on the simple side.. but did you check your cat converter shields? (all three of them)..

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post #7 of 10 (permalink) Old 06-30-2004, 01:48 PM Thread Starter
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Ya, underbody parts are solid. Its most likely inside the motor somewhere. I've started it twice with the 10w-30 and so far it hasn't done the rattle yet. I'll just have to see.

1989 Chevrolet Caprice 5.0L 75k
1994 Ford Thunderbird 4.6L 85k
Mods:Air Silencer Removed.
1996 Chevrolet Caprice 9C1 5.7L 130k
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post #8 of 10 (permalink) Old 06-30-2004, 03:23 PM
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If it's only at startup, then it may be due to the oil draining off the bearings, and causing a rattle. I've heard this many times. The bearings may not be shot, but I bet they're not exactly spec either. I would get a good oil pressure guage setup and se what you are really running. Get rid of the idiot guage that is in the insturment cluster since it really only tells you that you have pressure, but not how much. You could diagnose more from that as well.

These are highly engineered precision vehicles, the first step in diagnosing the problem is to strike the suspected offending part sharply and repeatedly with a blunt object, then re-test.
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post #9 of 10 (permalink) Old 07-01-2004, 01:30 AM Thread Starter
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Upon changing back to 10w-30 the rattle has disappeared. I'm curious to know why, but I'm not going to be putting 5w-30 back in anytime soon.

1989 Chevrolet Caprice 5.0L 75k
1994 Ford Thunderbird 4.6L 85k
Mods:Air Silencer Removed.
1996 Chevrolet Caprice 9C1 5.7L 130k
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post #10 of 10 (permalink) Old 07-01-2004, 02:34 PM
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mark 8's have a problem with the oil draining out of the cam tensioners when you shut the car off. when you turn it back on there is a nasty rattle until the cam tensioners pump back up. That's what this problem sounds like, but i don't know if it's a common SOHC problem or not. If that's what it is, it's nothing to worry about, just a NVH issue.
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