Engine Mount Heat Shielding Rattle

[cham]

I've been dealing with this nasty front end clattering for some time now and it's definitely in my best interest to start narrowing things down here in case it is the worst possibility.  The realm of possibilities of course include; broken timing chain guides, accessory belt pulley bearings, exhaust shield rattle, and rattling honeycomb within cats.  I guess you could include transmission but to me it sounds like its coming from the front of the vehicle and since its started, nothing has changed with the condition of my trans.  It is a definite metallic clanking/rattling that happens between 1750 and 2000 rpm in 1st and 2nd for sure; by 3rd and 4th I'm going too fast to be able to hear if it happens then as well (so only under load; does not produce noise in Park).  

 

Now the heat shielding covering my engine mounts on both sides definitely rattle significantly when I strike them, not sure if they are the culprit but I guess it's possible.  How might I go about securing them as hose clamps don't really work in this situation.  Yes I have checked exhaust shielding underneath the car and the shielding between my passenger side resonator and the chassis is the only thing that rattles at all, and I have to hit it to rattle.

 

Any ideas how I could narrow this down further; I saw another post with a similar situation but there was never a post on the discovered source.  I'm thinking if this goes on too much longer I might just bring it by a dealership for a diagnosis but in some ways I'm not sure if I trust them to be thorough enough, I could see how it would be easy for them to recommend the most expensive job as I guess it's kind of subjective what is producing the sound.

[Mrelcocko]

I know this is on a totally different vehicle but on my girlfriends 2000 maxima I had a similar sound that you’re describing and it ended up being an engine mount. Hopefully this might help you out some.


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[cham]

When you say engine mounts do you mean the literal bushings themselves rattling or the heat shielding covering the engine mounts?

[Slartibartfast]

Not making the noise when you rev it in neutral makes me think it's not a timing chain guide or an accessory bearing (they shouldn't know if it's in gear or not). When the cat honeycomb broke free on my friend's Chevy, we found it pretty quickly by smacking the exhaust from underneath and listening for the rattle. Sounds like you've ruled that out too.

 

Start with the shields you know are loose. If you can't get a hose clamp around them, try baling wire. I think I still have baling wire wrapped around a loose U bolt on my exhaust. That one caused a rattle from the transmission area, but only at part throttle/moderate load, which had me much more worried than I should've been.

[cham]

It seems that the only rattling I can find is just very slight rattles from my flicking on the shielding.  Its unfortunate because the one in particular on the passenger side is the large shield between the exhaust and chassis/uni-body so I cannot wrap a hose clamp around that either.  Thought for a second steel wool could be a good damper for the sound but realized quickly that it can catch fire fairly easily.  Anyone know of some sort of material to wedge between the exhaust plates that will dampen rattle while being non-flammable?  Maybe exhaust wrap would be the ticket.  

 

On top of that the engine mount exhaust shields rattle if I strike them but holding some sort of object against it, and then striking again nullifies the rattle.  Just don't know how to stop something like that permanently not to mention how hard it is to reach them.  Beyond that the catalytic shields seem fine and the manifold shields don't seem to rattle.  I do get a slight rattle when idling from a cold engine that just seems to come and go randomly until the vehicle is fully warmed up, but the sound is no doubt a heat shielding rattle (not as bad as the rattle under load).  I think I'll try starting the car and probing if I can induce any sort of continuous rattle from striking the shielding.

Edited June 29, 2023 by cham

[onespiritbrain]

Have you checked your mass airflow sensor? If its dirty then your ECM might think there is less air than actual causing a lean condition and ultimately a spark knock under load.

 

Spark knock can sound VERY much like a heat shield rattling

Edited June 29, 2023 by onespiritbrain

[cham]

So I discovered or I should say realized the rattle about a year ago right before a trip to Colorado.  I replaced my airbox filter a couple times during the trip just because of dusty conditions and did in fact clean my mass-air-flow sensor while I was out there with mass airflow cleaner.  I noticed the rattling before the trip so it was not a consequence of the dusty conditions out there. 

 

I have since tried using Premium (Usually used Mid-grade or Regular) to see if that halted any rattle/knock since the other forum thread I mentioned earlier did suggest this.  No change in the rattle, although I only tried this for one tank and I'm not sure if I need to try this for an extended period of time like a few weeks or so to let the ECM relearn.  If it is engine knock and premium were to fix it; would the problem then be a failing knock sensor?

 

Also I actually have a BlueDriver I bought to monitor coolant temps on long trips.  It shows live fuel trim and timing advance data and I'm curious if I could just use that to see if it is in fact engine knock.  The problem is I'm just not exactly sure how to conclude much from the data; I do realize the fuel trim percentages never get too far away from 0% when at a constant load or idle which I think means I'm not likely to have a vacuum leak or other ailment. 

Edited June 29, 2023 by cham

[onespiritbrain]

I have removed a lot of my heat shielding because it was all falling apart and I do not notice any issues with heat damaging components under there. I too have rattling and I'm almost positive it is coming from resonance in the exhaust piping itself. I have observed the pipe vibrating when the sound appears. But I can produce the sound in neutral..

 

Have you tried power braking to see if you can find a spot where the rattle appears? If you can force the sound to appear while stationary maybe you could back up against something completely solid (if you have a tow hitch or something that wont get damaged), like a giant cement structure that you're 1000% sure cannot move, and then have someone apply power until the rattle appears and then you carefully find it with a long stick. The rattling should stop when you jam a stick against it.

[Mrelcocko]

The maxima if I’m correct has 3 mounts and it ended up being the one on top of the engine. The bushings in it were toast.


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[cham]

I'll check the rocking of the engine when I shift into to Drive and Reverse but I don't believe it is anything out of the ordinary.  I guess if it does seem to be the issue that'll solve the engine mount heat shielding issue because I can replace them at the same time.  Any idea the kind of project it is to replace the mounts?

 

Something interesting to note is the rattle can be heard while driving in 1st or 2nd at around 1750rpms when the vehicle is warming up but once its warmed up to operating temperature it seems to go away almost completely.  If I shut it off and it sits for 5-10 minutes, then start the car again (already warmed up basically), it will start rattling again at 1750rpm for the next couple minutes of driving then stop again.

 

I have not tried power-braking, little worried about the torque of the vehicle overcoming the brakes if I tried this; no trailer hitch so no dice.  Is there any difference in revving the engine in neutral vs park?  I should note when I tried revving in Park I only really went to 2000rpms as that is where the rattle is while driving; since there is no load applied, maybe the rattle wouldn't be evident until its higher in the revs possibly?

Edited June 30, 2023 by cham

[onespiritbrain]

Mine rattles a lot louder under load and over a larger RPM range when the engine is cold. For instance when I drive up the hill after I pull out of my driveway in the mornings, the rattling is very pronounced and I can literally hear it echoing off of the houses as I drive by but if I have to go out to get food after I get home from work and the engine is still warmed up I can barely hear it at all except for right at 1800-1900rpm for a brief second. 

 

Im sure the loose or broken heat shielding or whatever is vibrating will eventually begin rattling even in neutral/park. You may have to wait until the problem can be identified under safe conditions.

[cham]

5 hours ago, onespiritbrain said:

I drive up the hill after I pull out of my driveway in the mornings, the rattling is very pronounced and I can literally hear it echoing off of the houses as I drive by

This!  Usually it’s the most pronounced when moving up a slight grade at neighborhood speeds (wind noise at a minimum and I’m in 1st or 2nd gear).  That was how I discovered it in the first place was if obstructions were close to the edge of the road, I could hear the rattle sound bouncing off the obstruction.  Now it’s obviously gotten loud enough to be heard otherwise.  
 

Why I initially was worried it could be timing components is that it basically goes away when everything is warm, I would think a heat shield rattle would happen all the time with the same intensity; apparently not the case.

 

Like I said earlier, sometimes when starting a cold engine I’ll get a rattle in park for a split second and it’ll come and go but not frequently enough for me to be able to catch it quick enough.  Hopefully the two rattles are related and it’ll get worse enough for me to pinpoint.  Wish there was a way to determine it’s not timing components for certain though.  
 

Thanks for the insight everyone, I’ll definitely keep this thread posted when I find the source.  If not I might take a trip to a mechanic.  Should I expect them to be able to find it any better than I can?

Edited June 30, 2023 by cham

[Slartibartfast]

I imagine a mechanic would go about it similarly to how any of us would, with the exception of having a lift for easier access to the underside, or maybe having a few more common culprits in mind.

 

Mine (VG engine) has a brief rattle on startup, especially if it's cold, especially if it's time to change the oil. That's just the lifters making noise until they see oil pressure, not sure if this is as common on the VQ. There is another ticking on mine that is worse when cold, and worse under load, and that's the exhaust leak. An exhaust leak at/near the engine can sound surprisingly metallic, and if it's a small leak, it may close up a little as the system warms. I don't know the VQ's weak spots for exhaust leaks, but if you're staring at the exhaust, keep an eye out for soot marks. (If it was a VG30, I'd say look for broken exhaust studs, but AFAIK Nissan had figured that one out by the time the VQ came out.)

 

Could be a heat shield no longer has room to rattle when the system is warm. I don't know the VQ well enough to say it's definitely not the timing components, but I would expect most internal noises to get worse as the engine warms and the oil thins. If it was pinging I'd expect the computer to be all kinds of unhappy, and if the knock sensor wasn't working, I'd expect it to complain about that, too. If you want to rule out a lean burn, check a spark plug. I worked on a friend's Buick once that was running lean and going into limp mode if he stepped on it. I suspect it was running lean and pinging, and the knock sensor was triggering the limp mode. All I know is the plugs were white and the MAF was filthy, and cleaning it resolved the issue. Doesn't sound like your issue. 

 

I like the idea of brakestanding it to see if you can make it act up, but, yeah, I wouldn't roll under a brakestanding truck. I'll bet you could clamp a pair of vise grips to the the shield you suspect of making noise, and take it around the block, and see if the noise goes away. Even if you can't vise grip the shield to something solid, I would expect the weight of the grips hanging off the side to silence the rattle, or at least change it somewhat. 

 

I have removed loose heat shields without issue. Easy when they're rotten. Harder when they're still welded/bolted on most of the way around.

[cham]

So I've got a little bit of an update actually.  I was installing my OME MD coils yesterday for the front drivers side when I accidentally dropped one of the strut tophat bolts down into the engine right as the strut was dropping down.  Spent the next hour trying to find it just to realize it fell behind the heat shielding for the catalytic converter.  Took some finagling but I got it out thank the lord.  Now in the process of looking for it I actually decided to remove the throttle body intake boot to get better access and well what do you know; I think I found the source of the rattle.  

 

Now prior to this when looking down at the exhaust manifold heat shielding you only really see the top side and then the heat shielding for the engine mount right next to it.  Apparently there is a couple plates underneath out of sight as well. While probing around for the bolt I felt the shield on the underside of the driver side manifold/headers rattling very obviously.  I could see this easily producing the clattering with the amount of play it has, especially being so close to the engine.  

 

Now the only question is how to secure it.  I'm thinking about taking some exhaust muffler tape to take up the slack on the loose shield and tape it to the upper manifold shield if that makes sense.  Could I use muffler tape in such a high heat environment at the headers?  What about JB Weld Exhaust weld?  It's in such a difficult position removing it is essentially impossible without removing a ton of stuff.  Regardless, thank you for bearing with me guys I hate to waste everyone's time on a simple heat shield rattle; I guess the fat lady hasn't sung yet, crossing my fingers.  

[Slartibartfast]

It's not every day that engine bay Plinko turns out to be a good thing!

 

I haven't used muffler tape or Exhaust Weld, but I'd be surprised if they held up for long that close to the engine/catalyst. The manufacturers likely list a maximum temperature, which you could compare with an IR gun to see if there's any hope. Metal zip ties are a thing, again I haven't tried them, but I've heard they're good. Depending on how the shield is constructed, how buried in the engine bay it is, and how it's failed, you might be able to weld or rivet the pieces back together. Personally, I would still reach for the baling wire.

 

Hopefully whatever you reach for is successful in silencing the fat lady. 

[cham]

Been a little while so I'll provide a quick update.  I ended up bending that driver side lower exhaust manifold heat shield down and then out for better access. I decided on some JB Weld Heat Weld Epoxy.  Seemed to do the trick at first and initially I thought I had completely fixed the rattling noise.  Couple days later the noise was back but in a less obvious way and in even more limited circumstances (it may have never completely gone away in the first place).

 

I then decided to take another look at that passenger side engine mount heat shield and figured out a way to secure it with a hose clamp underneath against the actual engine mount itself.  No more rattling on that heat shield when knocking it with my hand.  Days later I heard the rattle again destroying my confidence that I could ever make this rig reliable again.  Eventually I took another look at the manifold heat shield repair and what to you know the JB Weld had failed allowing play again.  The plan now is to just use a metal ziptie around the manifold and heat-shielding, hopefully that works.

 

Side note; I'm curious if wrapping a hose clamp around the upper heat shield plate of the engine mount and the lower base of the engine mount would transmit more vibrations because since doing it I cant tell if I notice vibrations at 50mph and 70mph more now.  I already know my driveshaft u-joints need some love (replaced my front-shaft u-joints myself but the shaft still obviously vibrates; should have gone with a fully rebuild shaft).  

[cham]

Well I finally got around to securing the driver side exhaust heat shield again and this time with a stainless steel zip-tie.  To my surprise no change, the rattle is still clear as day and I’m at whits end at this point.  I feel like I’ve checked every damn heat shield on that vehicle.

 

My next best guess would be to swap to a 40 weight oil and see if that quiets down the rattle at all; if it does i have my answer unfortunately.  If not I could try resetting the ecu and running premium gas for a couple weeks to see if it’s pinging for whatever reason; anyone know the best way to reset the computer before filling up with premium?

 

My last guess would be the accessory belt pulley bearings; how difficult is it to retention both belts after removing because they aren’t automatic tensioners.

 

 

 

 

[Slartibartfast]

If the noise went away for a while, that makes me think you were on the right track. Could be the zip tie isn't around the end that was rattling, or the engine moves under load in a way that slackens the zip tie, if it's on the engine mount.

 

IIRC the service manual has a procedure for resetting the computer (some Konami code entered by turning the key on and off and pushing pedals). Took us a couple of tries to get it right on my dad's R50, but it did work in the end, though of course it did not fix the issue we were chasing. Unhooking the battery for a while should work too. If it was pinging that hard, I would expect it to pull timing until it wasn't, or go into some kind of limp mode. 

 

I haven't done belts on a VQ. If they're like the belts on mine, they're a little fiddly to get to, but otherwise not too bad. If you're happy with the tension now, you could mark or measure the adjusters and just shoot for the same point when you put it back together, assuming you're re-using the belts. Not a bad idea to check the accessory drive, but again, if it's only making noise when it's in gear, I would not expect it to be an accessory or timing component.