knocking on cold start, very difficult hot-start

armchair mechanics, here's your chance to strut your stuff. my wild-donkey-guess is that somehow the timing is way off.
my 06 jetta 5-spd runs fine once started but has such difficulty with hot-starts that i've parked it, awaiting dealer-visit next week.
also it makes a heavy single-knock/rap on many cold-starts. that can't be good for the engine.
37k miles now. the issues started after my return commute from san jose -> boston. i did park it on top of a sprinkler head and it got watered from underneath for a few minutes, maybe that is a factor. ? doubtful. also:
right before the boston<->SJ commute, dealer swapped the fuel filter - it was clogged after 18k miles, and a fuel stop at a station that i realize in hindsight had old/crappy fuel. (500 ppm).
there it is.

Well.. you have a well trained Donkey... or as I always say.. "What an A$$". Timing.. I would be worried that you jumped a tooth.... A long shot is that the valve train was "shocked" causing something to jump.

Let us all know what the dealer says.

i just dropped it off at dealer. naturally it didn't really show the problem today, maybe because it's cool today. i'll report back next week with whatever they found. probably "problem not seen"...
as for that donkey thing, yeah, i get a lot of that, like the rodney dangerfield joke, "are you a t man or an a man"?

I have to ask. What type of oil have you been using?

i've been using castrol 505.01 from Tulley in NH (old bottles) as well as a bottle of the new castrol 505.01 from stevens creek VW in silly valley. i think the oil is the same but castrol just changed the bottle recently - that's what the silly valley parts counter dude told me, if i understood his non-boston-accent correctly. actually i haven't actually *used* any of the new spare 505.01 bottle yet, it still resides with the junk in the trunk.
westbound, when i stopped at my pals family non-farm in hastings nebraska , we checked the oil and it seemed way down - almost a quart down - below the jiggy part of the dipstick, barely any oil on the hang-lo at all. so i added 80% of my spare quart, leaving me with very little spare 505.01. but for the whole rest of the 7500 mile drive, it never seemed to be low.
i wonder if i overfilled it and did some damage? i don't think so, but i'm fairly paranoid. also, the first-case for me is always the rare "that will never happen" corner-case for the other 99.9999% of those on my home planet. that actually helps me with my paid-work, but it can be troublesome when it comes to mechanical stuff. that's why i never ventectomied any of our 3 TDIs which had the A4 style tank. (03 variant, 05 passat, 06 NB DSG).
ps - my pal in hastings has a stupendous diesel lawn-tractor. i think it's a john deere but it might be a husqvarna or susquehanna or australopithacus. but he now lives on a 1/4 acre lot and doesn't have much work for his tractor. i feel sort of sad for him re that, he's a true farm boy stuck in a suburban-style housing complex now. on the bright side, he's been going absolutely ape-feces terraforming some of the rough terrain in the common areas of his complex, and the neighbors don't seem to mind.
(you can count on me for TMI. no antishudder valve here, but my anti-shut-up valve works great.)

I'd be more worried about underfilling than overfilling. You have to be like 2L to be over full.

cool. thanks dhdenney. no worry then.
94 Z & formula, 1000 hp?! one of my many f-body cars was a 94 Z.
i really miss my Y2K Hurst Z28 but find the 05 GTOnaro to be a nice consolation for that. if you've got photos/web-page about your f-body cars, i'd love to take a look (i checked your "profile").

So, the first oil was TXT and the newer stuff is SLX?

My guess of the day. Put me down for a timming belt tensioner issue.

weed masticator, i'll go check that right now. i've got a bottle of each in the trunk. just got the car back... YES that's it. old bottle TXT new bottle SLX. also the new bottle is more cultured (labelled en francais).

regarding the starting issues: NO PROBLEM FOUND. yes, i'm a vehicular hypochondriac.
and right after i got it home, another long-crank hot-start when i had to leave again. apparently it's normal for a cold start to fire right up and a hot start to crankcrankcrankcrankcrankcrankcrank before turning over.
the knock-on-cold start had only happened a couple times.
as long as it starts every time, i won't worry. maybe if it recurs again i'll complain again on-record, 3 miles before warranty expires.

eli said:

a hot start to crankcrankcrankcrankcrankcrankcrank before turning over.

Click to expand...

If it is cranking, then it is turning over.

ok, you got me on that one, designated hitter denney.
must... not... sweat... small... stuff... like:
i just picked up my Holden/Pontiac GTO from the same dealership with an unintended modification: they jacked it improperly and crunched a plastic rocker panel.

eli said:

ok, you got me on that one, designated hitter denney.
must... not... sweat... small... stuff... like:
i just picked up my Holden/Pontiac GTO from the same dealership with an unintended modification: they jacked it improperly and crunched a plastic rocker panel.

Click to expand...

You're funny.

thanks DH. good news today - the dealership went all "CSI" in the shop, showing how their lift couldn't have caused the GTOnaro damage - there was no crunch underneath - only on the side of the panel. somewhat convincing... it must have been a significant/low impact while it was parked in their parking lot. the shop manager tried to tell me that the chick who inspected and signed "no dents / no damage" when accepting the car had "missed it". i was adamant that NO WAY was the damage there when I dropped it off- that their junior service chick didn't miss anything. bottom line is they are stepping up to replace/paint/bake/install the rocker panel at their cost.

did you ever figure out the problem?

im having almost the same excact issue with my 99.5 golf tdi. It makes a single knock on every start and like to take extra time starting when the motor is warm.