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Old 04-16-2012, 09:17 AM   #1
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Knocking sound from motor

I've noticed a knocking sound coming from motor 2 days ago. It's mostly when the Jeep is started up in the morning and it lasts until I'm half way to work (10 miles into my commute) then it goes away like nothing happened.

I checked my oil yesterday and it was below the (need to fill) line. I changed my oil a month ago and made sure I added enough. I've noticed a small spot when I park, but nothing that should have drained it that much. I added oil yesterday, but the noise persisted today.

If I drive for a while and then shut it off, and start it up again in about 20 min it knocks for about 5 seconds and then goes away. Check engine light has not come on at all, oil pressure ranges from 10-50 psi while driving, steady at 40 on highway. Anybody have any suggestions...

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Old 04-16-2012, 09:40 AM   #2
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What year, how many miles?

If you're levels are low, you could be burning oil.

My 97 TJ will knock a bit when it's cold, but she has 189,000 miles, so I'm not too surprised.

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Old 04-16-2012, 09:51 AM   #3
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What year, how many miles?

If you're levels are low, you could be burning oil.

My 97 TJ will knock a bit when it's cold, but she has 189,000 miles, so I'm not too surprised.
It's a 2000 with 91,000. It's been running great until 2 weeks ago, had to get a new radiator put in, and now this noise. It still runs great once warmed up.
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Old 04-16-2012, 09:56 AM   #4
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Almost sounds like the radiator isn't bolted in all the way and once it heats and expands stop's knocking around. Is the knock internal to the engine or are you feeling it as much as hearing it?
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Old 04-16-2012, 10:00 AM   #5
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I'm thinking maybe the oil in there is to thick. Running on 10-40 mine will tick loudly until warm. Running on 5-30 it hardly ever ticks because the oil gets to the top end faster.

This will also happen if you use any oil treatments like STP or lucas. They'll thicken the oil, thicker oil can't get to the top as fast. Once warm, oil thins out and your knock goes away.

Start by draining out all your oil, fill it with 5w30 and do not use any oil treatments. If it still knocks, you might need to run it a couple days and then change the oil again.

What oil was used when you just had it changed? 10w40? 5w30???? The higher the number the thicker the oil. As in, 10w40= 10 hot and 40 cold. 5w30 is 5 hot and 30 cold, a little bit thinner of an oil.

I started to notice this because mine would only tick for about a week right after every oil change until it thinned out a bit... with thinner oil, it will not tick even after my oil changes.
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Old 04-16-2012, 10:11 AM   #6
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What oil was used when you just had it changed? 10w40? 5w30???? The higher the number the thicker the oil. As in, 10w40= 10 hot and 40 cold. 5w30 is 5 hot and 30 cold, a little bit thinner of an oil.
Is that seriously what those numbers relate to? I've often wondered. I knew the lower the number the thinner the oil, I just wasn't aware one was the hot weight and one was the cold weight.
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Old 04-16-2012, 10:27 AM   #7
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I'm thinking maybe the oil in there is to thick. Running on 10-40 mine will tick loudly until warm. Running on 5-30 it hardly ever ticks because the oil gets to the top end faster.

This will also happen if you use any oil treatments like STP or lucas. They'll thicken the oil, thicker oil can't get to the top as fast. Once warm, oil thins out and your knock goes away.

Start by draining out all your oil, fill it with 5w30 and do not use any oil treatments. If it still knocks, you might need to run it a couple days and then change the oil again.

What oil was used when you just had it changed? 10w40? 5w30???? The higher the number the thicker the oil. As in, 10w40= 10 hot and 40 cold. 5w30 is 5 hot and 30 cold, a little bit thinner of an oil.

I started to notice this because mine would only tick for about a week right after every oil change until it thinned out a bit... with thinner oil, it will not tick even after my oil changes.
I used 10w40 Shell oil. Maybe I'll do a change and put in 5w30
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Old 04-16-2012, 10:28 AM   #8
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Almost sounds like the radiator isn't bolted in all the way and once it heats and expands stop's knocking around. Is the knock internal to the engine or are you feeling it as much as hearing it?
It's def coming from the engine, the radiator seems to be in tight.
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Old 04-16-2012, 10:32 AM   #9
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Quote:
Originally Posted by sevenservices
I'm thinking maybe the oil in there is to thick. Running on 10-40 mine will tick loudly until warm. Running on 5-30 it hardly ever ticks because the oil gets to the top end faster.

This will also happen if you use any oil treatments like STP or lucas. They'll thicken the oil, thicker oil can't get to the top as fast. Once warm, oil thins out and your knock goes away.

Start by draining out all your oil, fill it with 5w30 and do not use any oil treatments. If it still knocks, you might need to run it a couple days and then change the oil again.

What oil was used when you just had it changed? 10w40? 5w30???? The higher the number the thicker the oil. As in, 10w40= 10 hot and 40 cold. 5w30 is 5 hot and 30 cold, a little bit thinner of an oil.

I started to notice this because mine would only tick for about a week right after every oil change until it thinned out a bit... with thinner oil, it will not tick even after my oil changes.
I think you know what you meant, but typed it wrong. The first number is the cold viscosity, ( Hence the W by it for Winter ) the second number in a multi-viscosity oil is the hot viscosity. So, 5w-30 is a 5 weight cold (pumps easier) and a 30 warm (protects better).
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Old 04-16-2012, 11:18 AM   #10
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If it's a bad lifter, would it stop knocking after it warms up?
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Old 04-16-2012, 11:31 AM   #11
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A lot of videos on youtube seem to be similar, and some talk about broken lifters or pistons, I'm just wondering if they would quiet once jeep warmed up or drove for a while.
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Old 04-16-2012, 11:38 AM   #12
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I started noticing that my 4.0's knocking/tapping sound got considerably louder after I changed my oil last. I used 10w30, but I did put a quart of lucas oil additive in it, and I am now starting to wonder if that is my problem. It does make since, because the sound begins to fade as mine warms up too. I guess I am going to change my oil out and see if it makes any difference.

Is there any downside to running 5w30 instead of 10w30 in warmer climates?
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Old 04-16-2012, 12:17 PM   #13
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A lot of videos on youtube seem to be similar, and some talk about broken lifters or pistons, I'm just wondering if they would quiet once jeep warmed up or drove for a while.

Yes, piston slap can be common and will quit after warming up. They can also last a while, for ex. My 98 2.5L. Been knocking when cold for a little over a year, then last week:



#4 piston skirt broke off.

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