Piston Slap: Vapor Lock and the Hot R32?

Sajeev Mehta
by Sajeev Mehta
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piston slap vapor lock and the hot r32
Nick writes:I bought a used 2008 Volkswagen Golf R32 with 48,000 miles in January 2010 (5,000 only in the U.S., 3.2-liter NA V6). Every summer since then I’ve had issues as the weather warms up. Basically, it starts to act up when driving at around 85+ miles-per-hour or so, and it gets even worse if I’m stuck in any kind of stop-and-go traffic. The only sure fix is letting it sit and cool off for 30 minutes or longer.Typically, right after starting off at a light, I’ll get a second or two of power before the power suddenly drops off and the car kinda burbles and burps. The tach will start to jump if I mash the throttle, but otherwise the revs stay on the low end of the gauge. When forced to drive in this condition, the computed mileage doesn’t seem to suffer, but going something like 20 miles once drained a quarter of a tank. More recently, for the first time ever, it actually died in an intersection and the battery light came on. Once I got it stopped and in park, it restarted fine.I don’t get backfires. Others said they’ve noticed a strong gas smell at the car’s rear but I don’t think they observed drips.I love the car except for this problem no one can figure out. The only theory others have offered is a fried fuel flow sensor. With the gas and recent engine stall, I wonder if it’s just flooding the engine or something.Sajeev answers:This has to be vapor lock!Considering how jammed in that motor is in a VW Golf, the comments on this forum and the extensive diagnosis (?) time you’ve spent with mechanics — man, it’s gotta be vapor lock.But how do you fix it?You must protect the fuel line(s) from engine heat. Odds are that the area shown in the forum link needs said protective shielding, but there’s a chance that shielding isn’t enough: it can only do so much in an cramped compartment so thoroughly heat soaked. Cooling down a heat soaked shield could be worse than the initial problem, but try shielding the fuel rail first.If that fails…dare I say it? It’s time for a boy-racer aftermarket hood with scoops, vents or something — anything to expose the engine to outside air. Maybe you can get a carbon fiber one if you like that look. I personally dig this unit if painted to match the rest of the car, but maybe it’s not vented aggressively enough for the VR6 motor.Regardless, it’s certainly better than the stock hood, though you can also cut holes in your hood and install any sort of vent you wish. Hmm, the scoops from the 1987 Ford Thunderbird Turbo Coupe would look pretty sweet.Off to you, Best and Brightest![Image: Shutterstock user wavebreakmedia]Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.
Sajeev Mehta
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  • Adub Adub on Feb 17, 2016

    I hope you read this because it is probably NOT vapor lock. This is a fuel pump problem. The in-tank pump overheats and fails. Once it cools down, it'll restart and run fine. The pump will diagnostic test just fine in the shop, but it will strand the dealer mechanic five miles down the road on a hot summer day. Once the pump was swapped out, no more problems. Not sure what causes the pump to fail the first time, but most of the cars I've seen with that problem either got gas with water (premium in low traffic areas) or had a high ethanol content. In every case, replacing the pump solved the problem. Believe me, when customers say they can only drive their car at night or when it is cold, you pay attention.

  • Vdubgod Vdubgod on Apr 09, 2020

    Yes. I have this car it's a real piece of . It's not vapor lock though. The fuel tank has a design flaw and it builds up vacuum and starves the fuel pump.

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