Help diagnose this noise 2

Hi group,

I own a 2000 Jeep Wrangler 4.0 Automatic with about 70K miles on it.
After a period of driving at slightly heavier than normal engine load
on hot days, a knocking sound starts coming from the engine
compartment.

I think that the noise I've been experiencing is most likely coming
from within the engine or maybe the transmission. The first time I'd
experienced it I was driving through some sandy washes in Mojave. As
the engine and transmission load in the sand increased the engine
temperature went up (but well within the safe zone) and I started
hearing at first a tapping noise that gradually grew louder to a
pronounced knocking (like a small hammer hitting metal) in sync with
the engine RPMs. I stopped and put the transmission in park with the
engine idling, but the knocking continued. I opened the hood and tried
to listen where the knocking was coming from. It was pretty loud and
hard to tell where in the engine compartment it was coming from. It
almost felt like I was hearing it louder from under the vehicle when I
leaned down and listened to it from the side while looking at the
transmission.
At that time, I shut the engine off and waited for about 15 minutes.
Then I started the engine and the knocking was gone. I continued
driving slowly at lower gear in order to reduce the load on the engine,
which seemed to help. But still the knocking would come back at times
and I had to really slow down or stop for it to go away.

The best guess, I figured from the frequency of the knock (about
8/sec), would point to a something occurring every other engine
revolution like a valve.

When I first got the Jeep a year ago, I had no trouble driving up a
long hill on a paved road at a fairly normal rate of speed. Now a
couple months ago, I experienced the knocking again as I drove on a
road like that (paved, no sand) to the mountains on a hot day.
Most recently, I started hearing the knocking slightly after a period
of stop-and-go driving on pavement in rather benign hilly area.

So the knocking seems to start after a period of heavier than normal
engine load on hot days (though the engine temperature gauge always
remains well within the safe zone).

I would appreciate any ideas on what this might be and what if anything
can be done about this.

Thanks.

My first guess would be a crack in the exhaust manifold.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

jeepeeyes wrote:
>
> Hi group,
>
> I own a 2000 Jeep Wrangler 4.0 Automatic with about 70K miles on it.
> After a period of driving at slightly heavier than normal engine load
> on hot days, a knocking sound starts coming from the engine
> compartment.
>
> I think that the noise I've been experiencing is most likely coming
> from within the engine or maybe the transmission. The first time I'd
> experienced it I was driving through some sandy washes in Mojave. As
> the engine and transmission load in the sand increased the engine
> temperature went up (but well within the safe zone) and I started
> hearing at first a tapping noise that gradually grew louder to a
> pronounced knocking (like a small hammer hitting metal) in sync with
> the engine RPMs. I stopped and put the transmission in park with the
> engine idling, but the knocking continued. I opened the hood and tried
> to listen where the knocking was coming from. It was pretty loud and
> hard to tell where in the engine compartment it was coming from. It
> almost felt like I was hearing it louder from under the vehicle when I
> leaned down and listened to it from the side while looking at the
> transmission.
> At that time, I shut the engine off and waited for about 15 minutes.
> Then I started the engine and the knocking was gone. I continued
> driving slowly at lower gear in order to reduce the load on the engine,
> which seemed to help. But still the knocking would come back at times
> and I had to really slow down or stop for it to go away.
>
> The best guess, I figured from the frequency of the knock (about
> 8/sec), would point to a something occurring every other engine
> revolution like a valve.
>
> When I first got the Jeep a year ago, I had no trouble driving up a
> long hill on a paved road at a fairly normal rate of speed. Now a
> couple months ago, I experienced the knocking again as I drove on a
> road like that (paved, no sand) to the mountains on a hot day.
> Most recently, I started hearing the knocking slightly after a period
> of stop-and-go driving on pavement in rather benign hilly area.
>
> So the knocking seems to start after a period of heavier than normal
> engine load on hot days (though the engine temperature gauge always
> remains well within the safe zone).
>
> I would appreciate any ideas on what this might be and what if anything
> can be done about this.
>
> Thanks.

Mike Romain wrote:
> My first guess would be a crack in the exhaust manifold.

I'd also suspect a bad plug or carbon buildup in one cyl
that is causing detonation. Time to pull the plugs and
check. I'd think if it was manifold the noise usually
changes over temperature. Some cracks close some open
all depends on what side of the pipe they are on. Not
saying it couldn't be though.

> jeepeeyes wrote:
>>
>> Hi group,
>>
>> I own a 2000 Jeep Wrangler 4.0 Automatic with about 70K miles on it.
>> After a period of driving at slightly heavier than normal engine load
>> on hot days, a knocking sound starts coming from the engine
>> compartment.

<snippy>

Had a neighbor across the street when I was growing who owned a parts shop.
He used to take a large screwdriver and hold the handle to his ear, touching
the blade to various parts of the engine. Could tell very accurately what
was amiss. It does take a little practice.
D

"jeepeeyes" > wrote in message
ups.com...
> Hi group,
>
> I own a 2000 Jeep Wrangler 4.0 Automatic with about 70K miles on it.
> After a period of driving at slightly heavier than normal engine load
> on hot days, a knocking sound starts coming from the engine
> compartment.
>
> I think that the noise I've been experiencing is most likely coming
> from within the engine or maybe the transmission. The first time I'd
> experienced it I was driving through some sandy washes in Mojave. As
> the engine and transmission load in the sand increased the engine
> temperature went up (but well within the safe zone) and I started
> hearing at first a tapping noise that gradually grew louder to a
> pronounced knocking (like a small hammer hitting metal) in sync with
> the engine RPMs. I stopped and put the transmission in park with the
> engine idling, but the knocking continued. I opened the hood and tried
> to listen where the knocking was coming from. It was pretty loud and
> hard to tell where in the engine compartment it was coming from. It
> almost felt like I was hearing it louder from under the vehicle when I
> leaned down and listened to it from the side while looking at the
> transmission.
> At that time, I shut the engine off and waited for about 15 minutes.
> Then I started the engine and the knocking was gone. I continued
> driving slowly at lower gear in order to reduce the load on the engine,
> which seemed to help. But still the knocking would come back at times
> and I had to really slow down or stop for it to go away.
>
> The best guess, I figured from the frequency of the knock (about
> 8/sec), would point to a something occurring every other engine
> revolution like a valve.
>
> When I first got the Jeep a year ago, I had no trouble driving up a
> long hill on a paved road at a fairly normal rate of speed. Now a
> couple months ago, I experienced the knocking again as I drove on a
> road like that (paved, no sand) to the mountains on a hot day.
> Most recently, I started hearing the knocking slightly after a period
> of stop-and-go driving on pavement in rather benign hilly area.
>
> So the knocking seems to start after a period of heavier than normal
> engine load on hot days (though the engine temperature gauge always
> remains well within the safe zone).
>
> I would appreciate any ideas on what this might be and what if anything
> can be done about this.
>
> Thanks.
>

"screwdriver is touching the fan blades" :-)

Just jokin'. You can get proper engine stethoscopes as well.

Dave

"D" > wrote in message
...
> Had a neighbor across the street when I was growing who owned a parts
shop.
> He used to take a large screwdriver and hold the handle to his ear,
touching
> the blade to various parts of the engine. Could tell very accurately what
> was amiss. It does take a little practice.
> D
>

Ayup, had a neighbor like that once out west of Amargosa. Called him
Old Screwdriver Head after he got a bit too close to the power steering
pump one day. Not an uncommon tactic, works best on old iron blocks
that tend not to ring as much as alloy ones. Lot safer to use a
stethoscope with a contact sensor.

D proclaimed:

> Had a neighbor across the street when I was growing who owned a parts shop.
> He used to take a large screwdriver and hold the handle to his ear, touching
> the blade to various parts of the engine. Could tell very accurately what
> was amiss. It does take a little practice.
> D
>
> "jeepeeyes" > wrote in message
> ups.com...
>
>>Hi group,
>>
>>I own a 2000 Jeep Wrangler 4.0 Automatic with about 70K miles on it.
>>After a period of driving at slightly heavier than normal engine load
>>on hot days, a knocking sound starts coming from the engine
>>compartment.
>>
>>I think that the noise I've been experiencing is most likely coming
>>from within the engine or maybe the transmission. The first time I'd
>>experienced it I was driving through some sandy washes in Mojave. As
>>the engine and transmission load in the sand increased the engine
>>temperature went up (but well within the safe zone) and I started
>>hearing at first a tapping noise that gradually grew louder to a
>>pronounced knocking (like a small hammer hitting metal) in sync with
>>the engine RPMs. I stopped and put the transmission in park with the
>>engine idling, but the knocking continued. I opened the hood and tried
>>to listen where the knocking was coming from. It was pretty loud and
>>hard to tell where in the engine compartment it was coming from. It
>>almost felt like I was hearing it louder from under the vehicle when I
>>leaned down and listened to it from the side while looking at the
>>transmission.
>>At that time, I shut the engine off and waited for about 15 minutes.
>>Then I started the engine and the knocking was gone. I continued
>>driving slowly at lower gear in order to reduce the load on the engine,
>>which seemed to help. But still the knocking would come back at times
>>and I had to really slow down or stop for it to go away.
>>
>>The best guess, I figured from the frequency of the knock (about
>>8/sec), would point to a something occurring every other engine
>>revolution like a valve.
>>
>>When I first got the Jeep a year ago, I had no trouble driving up a
>>long hill on a paved road at a fairly normal rate of speed. Now a
>>couple months ago, I experienced the knocking again as I drove on a
>>road like that (paved, no sand) to the mountains on a hot day.
>>Most recently, I started hearing the knocking slightly after a period
>>of stop-and-go driving on pavement in rather benign hilly area.
>>
>>So the knocking seems to start after a period of heavier than normal
>>engine load on hot days (though the engine temperature gauge always
>>remains well within the safe zone).
>>
>>I would appreciate any ideas on what this might be and what if anything
>>can be done about this.
>>
>>Thanks.
>>
>
>
>

Thanks for the responses.
I think that I will take DougW's advice first and look at the spark
plugs. I replaced all of them last year, but that does not mean one
couldn't fail.
Then, if they all look good, I will buy the stethoscope and carry it in
the Jeep ('cause it always happens out in the boondies) and probe for
the source of the knock the next time I hear it.
Oh, by the way, I've already inspected the exhaust manifold and there
seem to be no signs of cracks.

jeepeeyes proclaimed:

> Thanks for the responses.
> I think that I will take DougW's advice first and look at the spark
> plugs. I replaced all of them last year, but that does not mean one
> couldn't fail.
> Then, if they all look good, I will buy the stethoscope and carry it in
> the Jeep ('cause it always happens out in the boondies) and probe for
> the source of the knock the next time I hear it.
> Oh, by the way, I've already inspected the exhaust manifold and there
> seem to be no signs of cracks.
>
There are two major categories of mechanic stethoscopes. The
inexpensive ones are between $10 to $20 and are purely mechanical with
just air from the probe up to your ears--the earpieces are typically
earbuds. e.g. http://www.brandsonsale.com/ht-001057-images.html
For about $150, you can get the amplified version with the larger ear
mikes like a set of stereo headphones. e.g.
http://www.alltiresupply.com/p-OTC-3590.html

smack the cat. converter and see if it rattles if it does it is no good and
i have seen them make a noise that sounds just like a rod knockesp in the
trucks

jeepeeyes wrote:

> Hi group,
>
> I own a 2000 Jeep Wrangler 4.0 Automatic with about 70K miles on it.
> After a period of driving at slightly heavier than normal engine load
> on hot days, a knocking sound starts coming from the engine
> compartment.
>
> I think that the noise I've been experiencing is most likely coming
> from within the engine or maybe the transmission. The first time I'd
> experienced it I was driving through some sandy washes in Mojave. As
> the engine and transmission load in the sand increased the engine
> temperature went up (but well within the safe zone) and I started
> hearing at first a tapping noise that gradually grew louder to a
> pronounced knocking (like a small hammer hitting metal) in sync with
> the engine RPMs. I stopped and put the transmission in park with the
> engine idling, but the knocking continued. I opened the hood and tried
> to listen where the knocking was coming from. It was pretty loud and
> hard to tell where in the engine compartment it was coming from. It
> almost felt like I was hearing it louder from under the vehicle when I
> leaned down and listened to it from the side while looking at the
> transmission.
> At that time, I shut the engine off and waited for about 15 minutes.
> Then I started the engine and the knocking was gone. I continued
> driving slowly at lower gear in order to reduce the load on the engine,
> which seemed to help. But still the knocking would come back at times
> and I had to really slow down or stop for it to go away.
>
> The best guess, I figured from the frequency of the knock (about
> 8/sec), would point to a something occurring every other engine
> revolution like a valve.
>
> When I first got the Jeep a year ago, I had no trouble driving up a
> long hill on a paved road at a fairly normal rate of speed. Now a
> couple months ago, I experienced the knocking again as I drove on a
> road like that (paved, no sand) to the mountains on a hot day.
> Most recently, I started hearing the knocking slightly after a period
> of stop-and-go driving on pavement in rather benign hilly area.
>
> So the knocking seems to start after a period of heavier than normal
> engine load on hot days (though the engine temperature gauge always
> remains well within the safe zone).
>
> I would appreciate any ideas on what this might be and what if anything
> can be done about this.
>
> Thanks.