Same question I had when I first saw a post about it on this board... It appears to be a much overlooked part of maintenance of non-turbos that can cause oil seals to fail and more that I don't know and hope to avoid!

Following is info I cut from www.southwestauto.com/volvo_service.htm about it. And here is bay 13 site on replacement http://www.volvospeed.com/Repair/ftrap.htm The cost for flame trap & O ring from my local was $7.97 took me about an hour this first time and will probably go quicker now that I have an idea of what I am doing.


Most Overlooked Service: Flame Trap!
We at Southwest Auto sincerely thank you for your tremendous response to our first newsletter. We received many comments about the service article pertaining to flame traps. Most owners had never heard of this part, nor did they understand it?s importance in preventing major repair costs.

What exactly is a "Flame Trap"? As part of the positive crankcase ventilation (PCV) system of your Volvo?s engine, a properly functioning flame trap is an essential element in reducing exhaust emissions. Serving the same function as a PCV valve on a domestic vehicle, a flame trap is used to vent hot oil gases under pressure from the engine crankcase to the intake system where they are burned with the normal fuel thereby lowering exhaust emissions (pollution). It also serves as a flame barrier (hence the name "flame trap") in the event of an intake back-fire to prevent the oil vapors in the oil pan from igniting.

The flame trap itself is a corrugated brass screen or perforated plastic element which are serviceable. Failure to change the oil and oil filter on time can cause the flame trap element to become clogged as oil gases become heavier between oil changes.

When to Service the Flame Trap.
Volvo recommends servicing the flame trap every 15,000 miles for 1985 and older cars and 20,000 miles for 1986 and newer.

Failure to do this $25 service on time will cause the element to become clogged and create excessive internal pressure in the engine! Among other things, this leads to premature failure of engine seals, massive oil leaks, and an unnecessary $500 repair bill!