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2003 1.8T Passat sedan
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Discussion Starter #1 (Edited)
UPDATE BELOW
Hi all! not quite a vet member but let me know what you think about this.

2003 Passat 1.8t AWM with 012 5-speed trans
140K

--mostly relevant background--

Just replaced OE coolant flange, heater inlet hose, gaskets etc. Upgraded to cast flange.
Trans mounts replaced 3 months ago
GL5 trans fluid around the same time
Snub mount replaced ~8 months ago
OE engine mounts
compression tested ~6 months ago, ~140psi dry avg, no wet test
updated dealer warranty coils
new CVV
***034 billet PCV, plugged the smaller vacuum line that would have Tee'd into the regular PCV from the valve cover which to my knowledge is just there to prevent sludging, but I'm running synthetic and it ran well for a day after I installed with the coolant flange.
following that I did an oil change with LiquiMoly engine flush, molygen 5w40 following flush instructions. I do this ~4 changes
I filled the filter with oil before screwing it on
Clean air filter

---Current Problem---

I am actually about to get it jacked up in a little bit. I’m going to check out Trans and Engine mounts but I’ve never heard of them spontaneously failing? Last time I was under it I didn't see any Barney blood.

Problem while driving only manifests when foot comes off the gas, kind of like a Muffled whoooooom
only really audible up until 3rd gear and 4th doesn't really make any noises.

There is a loudish clunk when I take my foot off the gas at lower speeds <50mph and intermittently when I take off the clutch, hard to tell if it's L/R

Starter is fine.
At idle the whole car vibrates. It even makes the rocks in my door compartment rattle
Normal warm idle ~800-900.
Kombi valve does its thing cold starting after ~100 seconds.
No nasty engine noises, no misfire codes so IMO it's not timing or ignition. the whole thing is just rougher than normal
Doesn’t die at idle so I would rule out fuel or Turbo problems. I have not found any air leaks, sprayed carb cleaner around all my vacuum fittings. definitely makes boost when I'm 1:1 throttle in 2nd gear.
Throttle is clean however I did notice it's not closed completely flush with the bore +/- 1mm hardly. not sure if that's normal or if it needs to re-learn.

At this point I’m reaching for straws. I would think that maybe when I poured in the engine flush it loosened some gunk and clogged somewhere. maybe the oil pickup? piston squirter?
I really doubt it; the car drives and that's what the flush is designed to do? break up sludge... No bad turbo noises.
Either that or a bad engine mount, however revving in neutral I don’t see the engine really moving more than it should.
Anything general you’d recommend to check?

I don't have a vacuum gauge- my old one broke, however brake booster works from a pedal perspective,
whatever that's worth.
I have checked around the B5 Garage for similar threads but my issue seems to be different than others.

UPDATE
I tried using my UV flashlight and it would appear that the hydraulic fluid is reflective. I'll check it out further when I put the new ones on. See photos below.
Thank you to everyone that responded


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My guess broken motor mount (not the metal portion, but the rubber isolator) is a common problem.

Flushing the engine and oil squirters WILL NOT make something go clunk.
 

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It can be, they are fluid filled and once they leak, they can make noise. Did you adjust the snub mount once it was installed? It should be centered in the holder. If not, it can add vibration and cause thumping if it's hitting the top all of the time and make noise when it moves quickly down when slowing.
 

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The it's likely either a bad motor mount or loose subframe mounts/bolts.
 

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There is a loudish clunk when I take my foot off the gas at lower speeds <50mph and intermittently when I take off the clutch, hard to tell if it's L/R

I have not found any air leaks, sprayed carb cleaner around all my vacuum fittings.

...revving in neutral I don’t see the engine really moving more than it should.
Some observations: Take another look at those trans mounts. Try setting your parking brake, then have a helper simulate starting off in first, then in reverse, while you get your eyes low enough to watch the back end of the trans. The rear of the transmission will move down when easing the clutch out in first, and lift when doing reverse. A broken rear mount might be revealed this way, especially if you hear the clunk.

Go easy on the carb cleaner as a test-spray. That stuff often contains aggressive solvents like Toluene or MEK; not healthy to breathe or get on your skin, plus can be hard on materials other than metals.

Revving in neutral doesn't apply much torque to the mounts, so watch the engine for excessive movement (lift up, pitch down, twist opposite crank rotation) using brakes applied as for the trans mount test.
 

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Discussion Starter #9
have a helper simulate starting off in first, then in reverse, while you get your eyes low enough to watch the back end of the trans. The rear of the transmission will move down when easing the clutch out in first, and lift when doing reverse. A broken rear mount might be revealed this way, especially if you hear the clunk.
Simulate how? Putting it into gear while its lifted and turn the front wheel(s) ?
I'll look at the trans mounts tomorrow and see what's up. I aligned the holes in the subframe and tightened the brackets down evenly.

I have driven the car to work this week and it is much better than it was before, I still get some roughness in 1st and reverse unless I'm very easy on the clutch. Should I be looking for tension or looseness in the trans mounts? They were installed a few months ago and felt like they settled almost immediately, I'll know when I see though.
 

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With the motor mounts looking like they lost their fluid a long time ago, I would just go ahead and change them. I don't think the new trans mounts have failed that quickly, but if they did, it's because the motor mounts are shot.
 

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At idle the whole car vibrates. It even makes the rocks in my door compartment rattle
That would steer me away from it being an axle issue given that when at idle on a manual trans, you either have the clutch pushed in, or you are in neutral.

But for completeness, what brand axles did you get?
 

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Discussion Starter #14
That would steer me away from it being an axle issue given that when at idle on a manual trans, you either have the clutch pushed in, or you are in neutral.

But for completeness, what brand axles did you get?
Some remanufactured axles, no problems
After replacing the engine mounts I no longer have the huge vibration problem, the car feels stiffer too which is good. Also found that the driver side subframe bolts were just snug enough to be tight which doesn’t surprise me a bit.
however now vibration only manifests when I take my foot off the gas in low gears and reverse. If I’m gentle into 3rd it doesn’t seem to do it. Reverse is the worst, it will rumble unless I’m just barely letting the clutch off.
I also saw someone on this thread talking about a rear trans mount. I only have two L/R but I think the 4Mo has a bridge-looking mount right before the drive shaft?

In forward gears almost feels like the problem is coming from the snub mount, like rise and fall, but I checked it out everything seems fine.
I can get it lifted today, good chance the trans mounts could vibrate themselves loose in a month?
 

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Even the 4Mo had only 2 trans mounts. There was an aftermarket 3rd mount, called a DTS (drive train stabilizer).
Bolts not torqued properly can work their way loose. When did this problem start and what was done shortly before it started?
 
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Discussion Starter #16
Problem started right after I was working on the cooling system for a few days and then changed the oil.

Update

I found the passenger trans mount was loose on the two 14mm bolts that go upward, also I am running an ECS aluminum skid plate which was slightly interfering with the snub mount bracket. Moved it forward a bit and checked all the remaining trans hardware and the car drives fine now.
🤦
 
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