Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

I again blew through the flame trap with compressed air. I plan to drive the car about 1,000
miles and replace the oil and filter again. I know this is probably sacrilege to some but I think this
is the fix. The motor is no longer blowing oil out the breather. [Response 4: Don Foster] I had
luck with carb cleaner, a coat hanger, and compressed air. I sprayed the cleaner in and let it
soak 45 minutes before blasting the crud through with compressed air. I followed with a quart
of Gunk Motor Flush (I think it's only kerosene or diesel fuel). Then I drove the car 25 miles and
changed the oil. In my opinion, if you tried to pour anything down there while the engine's idling,
you'd end up wearing most of it. The only reason I didn't remove the oil separator is because on
an '82, with K-jet, the separator's buried. It would have been a two-day job to remove and clean
it. On the B230 engine, it's a half-hour job to do it correctly.
[Tip from Ralph Haber] This may seem obvious, but can be easily overlooked. During a recent
oil change and flame trap replacement, I decided to check for vacuum at the FT fitting. There
wasn't any. Closer inspection revealed that the hose and intake manifold nipple were completely
sealed off by a 10 year accumulation of dried oil/carbon and other yuk. No vacuum was present
at the flame trap fitting. Replacing the hose and drilling out the nipple gunk corrected the
problem. This was on a B230F engine in a 89 744GL with 189K on it. This is real easy to check
and can be rectified with a minimum of effort. Untreated, it may allow unwanted pressure to
accumulate in the crankcase leading to oil leaks and blown seals. [Related Tip from Steve
Roop] The intake manifold vacuum fitting (small) going to the flame trap was hopelessly
clogged. After struggling with trying to clear the blockage and wanting to get to bed in this
century, I found that a 3/32 drill bit, turned slowly, would clean out the nipple perfectly (of
course I removed the fitting from the intake manifold first!). Anyway, it really speeds up the
cleaning process and I now pass the jiggle test again. [Tip from Mike W.] If the manifold fitting is
plugged, the hose between it and the flame trap surely is also, and should be replaced.
[Inquiry:] Why not just leave out the flame trap? [Response: Editor] The flame trap prevents
any engine backfires from reaching blowby gases in the crankcase, which would otherwise
cause catastrophic results. It is an important part of the engine and must be left in place. Since
cleaning it is not hard, there is no reason to remove it.
[Inquiry: Stuck Flame Trap] In the Volvo dealership where I worked as a tech for quit a long
time, what we did to get the flame trap out was take your screw gun and shoot a small screw
partially into the center hole in the lil bugger. This gives you a handle to pull it out with and
makes it very easy to change. Otherwise you'll screw around all day trying to get it out.
Crankcase Pressure Gauge and Tester. [Tips from Don Foster] To measure crankcase
conditions, I built a vacuum gauge to quantitatively measure the actual vacuum. I started with a
modified oil cap, shown below. It's an older style metal cap into which I soldered a brass barb
fitting, available at any hardware store. One could use a plastic cap with the same fitting, glued
with Goop or a similar adhesive.