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My ’95 VW B4 Passat 1.9td (AAZ engine) with 335 000 kms on the clock has an obnoxious plop coming from the engine when it is hot. Revving it causes the noise to go away for a short while. The oil was changed about 1000 kms ago by first running fully synthetic for a couple of days, then switching to semisynth, and the filter was changed both after draining the old oil, and after draining the flush oil. I also just replaced the thermostat and coolant, which made the problem worse, since it now reaches operating temperature much quicker.
You can hear the noise from the start of this video. After revving, it reappears at about 48 seconds.
[video]https://www.youtube.com/watch?v=94g1Q0Uu1pY[/video]I do not recall when the problem started, but it is entirely possible that it developed while on the flush oil. Both that, and the oil that’s currently in the engine is generic 10W-40, so my current diagnosis is: Incorrect oil for this engine. But I’d really like some other opinions and ideas before I spend the money on “proper oil”.
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Sounds like a lifter. Pumps up with increased oil pressure and bleeds off at idle (extreme wear?). How does it act on cold start without revving?? I’m not a Volkswagen guy. Does it use cam followers or push rods?
When it is completely cold, it plops for a couple of seconds after startup, then quiets down until it’s hot. The head uses a single cam with what I’d call “regular” hydraulic lifters (not pushrods).
When the oil is cool it is more viscous and when it warms gets thinner and pressure drops some. The symptoms fit worn lifters and you really can’t test the compression on a diesel without special adapters. If you want to bother, you might pull the valve cover and check the lash (press on the lifters) when the engine is cold so you might identify which lifter(s) need to be replaced. Not sure if you have access to used parts, I do here and would probably go that route on an engine with that many miles.
Also make sure you are using the MFG recommended oil viscosity.
10W-40 is the recommended viscosity, as far as I know. It was running on thicker oil when I got it though, since the previous owner just gave it what he had for his farm equipment.
EDIT: Some form of Castrol Universal.
Go to the parts store and buy turbo diesel oil. Say rotella 5w-40 or mobil 5w-40. Standard oil will not work in these engines. It has to be turbo diesel oil.
Refer here. http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/1336499/VW_1.9L_TDI_Motor
You may have a cam follower problem. If so time to replace lifters and possibly cam.
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