For years there has been a lot of contradictory information surrounding
the results of using Bosch Platinum spark plugs. These myths and legends
had bled over into Volvo 850-dom, which I found odd, as the 850's engine
management system is by Bosch, and also because they worked so well for
me! Further, even after I'd proclaimed the Bosch Platinum plugs fit for
(even severe) service in my 850 Turbo, it seemed like some owners of these
cars had a remaining aversion to or doubts about Bosch Platinums, likely
due to lingering doubts over these persistent myths and legends and
mechanics' tales.

After a bit of digging, I came up with a phone number for Bosch technical
support: 800-521-5462

(While I was "only" asking spark plug questions, I was left with the
impression that this might be a useful resource for solving a stubborn
Motronic problem as well.)

I will now attempt to debunk for you the myths and legends surrounding Bosch
Platinum spark plugs:

Bosch acknowledges a problem with using their Bosch Platinum spark plugs
in engines with ignition systems that employ 1 coil for each pair of spark
plugs (also known as a "waste spark ignition system").

In cars with conventional (1 coil, distributor/rotor) ignition systems
(including the 850 Turbo with Bosch 4.3, 4.4 engine mgmt systems), there
is no problem. In fact, not too surprisingly, according to Bosch, the
maker of the 850's engine management system, the recommended plug is the
Bosch Platinum FR7DP, which is what passed with flying
colors my tests-under-fire in my engine (see for yourself).

The problem that Bosch has acknowledged when using their Platinum plugs
in engines with waste spark ignition systems stems from the tendency of
electrode metal to get transferred depending upon the polarity (direction
of current flow) of the spark. In waste spark ignition systems, 1/2 of the
plugs always see reverse polarity sparks. Given the very narrow platinum
center electrode of the Bosch Platinums, performance will be degraded more
significantly when reverse polarity sparks will cause material to be
transferred from the large ground/outer electrode onto the narrow platinum
center electrode's exposed end surface.

In cars with conventional (1 coil) ignition systems, every spark is of
the same polarity, for which the Bosch Platinums are optimized, leaving
them to deliver their designed-in advantages, which include:

o reaching self-cleaning temperature faster ("than any other plug")

o maintaining the spark gap and low firing voltage requirement throughout
their service life. (even in my high-stress turbocharged application)

While there remain some cars with conventional ignition systems which
do not seem to get along very well with Bosch Platinums, which seemingly
no one can explain (maybe all their sparks are of the 'wrong' polarity
in some cases), they did and do good work in my '95 854 Turbo.

- Dave [Image]
"Unidirectional tires are a mixed blessing on cars that go equally fast in both directions."
  ------------------------------------------------------------------------
Re: Debunking the Myths & Legends: Bosch Platinum[850/95] posted by abe crombie on Saturday, 5 September 1998, at 12:45 p.m.

The only problem that Bosch Platinums ever had was with cold fouling due to
the subsurface center electrode. If you start the engine and shut it down
for a couple of times with a break of over one hour between the starts in
cool to cold weather you will likely create a flooding condition and the
BP's will foul. The spark finds the conductive path from the electrode up
and over the ceramic insulator instead of jumping the gap to ground
electrode in a manner that would produce effective spark for combustion.
I have used them and know of many people that have used them successfully
but I also know many people that wreckered cars with relatively fresh sets
of BP's in the winter time after they started car to move it around in drive
and then retried to start it later and it would miss and then die and not be
able to be started. Those plugs upon removal and insertion into a plug wire
will bleed spark down the sides of center electrode. The solution is to
NEVER start your car in cool to cold weather and not allow it to reach full
operating temp. This is the way it should be regardless of what plug is
screwed into your engine. These short runs put HIGH levels of moisture in
oil that forms acids when it is not boiled out by the engine reaching full
operating temp and being maintained at that temp for at least 8-10 minutes.
Starting a car and letting it warm up is not good for this reason. You
should start it and then drive off easily for a mile or so to allow gearbox
oil and engine to reach a warmer temp and then STAND ON IT! (of course,
obeying all local traffic laws and normal etiqette afforded to others on the
highways with you).

I have a 96 850 Turbo and several years ago while driving to the airport, it suddenly began missing like someone had pulled a spark plug—I had
previously installed Bosch platinum plugs after the originals reached the end of their service life.  To make a long story short, the dealer determined
a low compression in #3 and pulled the head.  Two burned exhaust valves, one of which had a chip on its rim.  The other cylinders and valves
looked fine. Of course, just a few thousand miles out of warranty, but Volvo agreed to pay half the $1500 cost. Everyone was perplexed as to why
this problem happened.

The other day, in chatting with an independent Volvo garage owner, I asked him about the above problem.  He said he had seen a number of
problems with platinum plugs in 850s, all due to the porcelain insulator breaking.  He thought my problem might also have been due to the
plugs—particularly in light of the chip on one of the valves.

Whether my problem was caused by the platinum plugs or not, I am not going to risk another $1500 repair and will stick with the standard Volvo
recommended plugs.

Jack Corneveaux

Park City, Utah  USA

• My name is lee and i am an ASE cetified technician. Over 20 times have I had customers cars in my shop with secondary ignition breakdown problems with bosch platinum spark plugs. I take out the bosch and screw in any other type of plug and the problem goes away. I dont sell bosch platinum. Regular bosch plugs seeem to be ok. The problem is so consistent that if I encounter a misfire and the car has bosch platinum my first step is to replace the spark plugs with any other brand.

• I agree 100% with Lee. In my humble opinion the Bosch Platinums are junk & iwill replace them. I prefer OEM in all cases ie; Champion in a chrysler, AC Delco in a Gm, & of course Volvo in a Volvo. Don in Tucson, AZ  -  ASE CMAT, L1

 

If you have any experiences, facts, hints comments or data that you think might be useful on the site, please

and I will post it, with an acknowledgement of your contribution (if you so wish).