What's the purpose of the bronze coil in the Volvo fuel injection system?

Dear Car Talk

Dear Car Talk | Sep 01, 1989

Dear Tom and Ray:

I've had a couple of Volvos that have taken me well over 100,000 miles each. One was a 1980, my current one is an '82. Here's the question. Both cars have, in a hose that snakes around the fuel injection system, a small bronze coil. When I bought the first Volvo, the coil was almost completely plugged with oily crud; I cleaned it but couldn't tell any difference in performance. The second one, which now has 160,000 miles on it, is pretty clean. The conventional wisdom of the mechanics I've discussed this with is that it's for fire suppression, that it's "overkill" by the Volvo engineers, and should be removed and discarded. Should I keep it or throw it away?

RAY: It's called a flame trap, and it's there for a reason. It's Volvo's version of the PCV valve. You know how the Swedish make meatballs their own way? Well, they make crankcase ventilation differently too.

TOM: The flame trap, or PCV valve in other cars, prevents explosions in the intake manifold from flashing back into the crankcase where unburned fuel can can turn your Volvo into a laser-rock show for the neighborhood kiddies. The problem is that most mechanics don't know what it is or where it is on Volvos, so they never change and it gets plugged up.

RAY: When it gets plugged up, the crankcase stops ventilating, and pressure in the crankcase will probably build up to the point where you start leaking oil. It's a $3 part. Replace it, and replace these mechanics too.

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