Images kindly supplied by vladimir
These 3 electrode OEM plugs came out of a n/a S70
-still pretty clean after 26000 miles!
Images kindly supplied by vladimir
These 3 electrode OEM plugs came out of a n/a S70
-still pretty clean after 26000 miles!
OzBrick: My tech friend recently recommended that I replace spark plugs at least every couple of oil changes or so. OK, this might be overkill, but it might also prevent wear on far more expensive ignition components such as ignition coils, which he has seen burned out on a number of vehicles. I put this comment up at Brickboard but it did not yield any response. So it is up to you to decide... Of course Vladimir's piccies above might be evidence contrary to this... I welcome any comments.
new 3 electrode Volvo plug
|
Added comment from Chris, (tech friend here in Sydney): All high energy systems should probably use plugs with at least a 1mm gap, changed at 15000km intervals city driving, 20000 on the highway. The FR6DC/FR7DC is a .7mm gapped plug which does not allow for a very large spark - the spark has to find fuel particles in order to ignite it (note that air by itself does not burn, it needs something like hydrocarbon fuel to ignite) and the larger the gap the more likelihood (especially with engines that run a very lean mix at idle, which includes the 850) that every spark will actually ignite fuel. This may explain the lack of power noticed by Bruce (below) with the .7mm gap plugs. I think that the Bosch book which recommends the DC is erroneous. So this problem may be resolved by using the DCX type plug (eg FR6DCX) which has a larger gap (about 1.1 mm). As for manufacturers with their specified 40000km intervals between changes, remember how wrong they were with oil change intervals - just ask any Honda V6 owner that has had a camshaft disaster ($$$$$!!!). (Ozbrick- and as we discuss on this site, the same is quite probably true regarding auto transmission fluid.) I recommend NGK plugs as a much better performer than Bosch, just from experience. NGK number for the 850 would be BCP5EY11. The plugs in the picture above are not that badly
worn, but they are still visibly worn. For any cheap consumable parts like
sparkplugs, don't penny-pinch. It will likely cost more in the long run.
In the case of sparkplugs we are talking about loading up the rest of the
ignition system, with consequent higher wear and tear on everything else.
The extreme illustration of this is that on many modern cars you can't
just pull off a spark plug lead because the system pumps out such a high
voltage under an open circuit condition that the potential energy has to
go somewhere. It goes back through the system until it finds an earth,
and can easily cook delicate electronics. These added stresses are most
likely to occur under high load situations - eg. just when you hit the
throttle to get up a large hill, when a higher voltage spike occurs through
the plugs at the instant that you hit that throttle. This leads to an engine
miss. The spark is opportunistic, and will go somewhere else (eg leads,
whatever) to get to ground-and this is where that added stress occurs.
|
... 3 electrode package information
Pardon a late follow-up question: I have a '94 850 non-turbo.
My owner's manual specifies a Bosch FR6DC spark plug, which Bosch no longer
makes. The Bosch data book at my local auto parts dealer says
I need a Bosch 7555, which corresponds to a FR7DC. When I installed those
plugs, properly gapped to .7mm (.028"), the car has much less
power. What can I do here?
Thanks for the info.
--
-- Bruce
Bruce-
One heat range hotter shouldn't make a noticeable difference
in performance. The recommended plug for non-turbo applications is a
three-electrode plug. I don't know any supplier other than Volvo
dealers. Did you torque the plugs? That has a large effect on working heat
range. I gap the single electrode plugs for turbo cars at .035"
or about .9mm and torque them to 18 foot-pounds with a dab of anti-seize
on the
threads. Were there any other changes to the car? Are you running
the BEST fuel you can find? You could try clearing the adaptation and see
if
that helps. The easiest way is to disconnect the battery for
a few minutes. Be sure you have the radio code or you will be tuneless.
(bummer)
Dave the Volvo Tech
'99 V70R AWD, '93 854 GLT, '82 242 DL
--
Dave the Volvo Tech
Hi Dave --
I bought the 3-electrode plugs from Volvo. They work much better.
My torque wrench has no settings below 20 ft-lbs, so I used the old Suzuki
motorcycle technique of tightening it "'til it feels pretty darn
tight but not so hard you strip the aluminum threads". (Well, it worked
OK for my last
13 years of Volvos...) I'll get a lower-range torque wrench before
the next plug change. I do use anti-seize on the threads (amazingly hard
to
wash that stuff out from under the fingernails).
About those "other changes": That same weekend I changed the timing
belt (I double-checked it last week and it is dead-on perfect according
to the Bay 13 procedure and pictures), serpentine belt, rotor
and cap. Gas is unchanged (mid-octane Arco) which runs well in our other
Volvos
('82 240, '86 740, '87 760 turbo). I will try 76 super, which
runs noticeably better in my '82 240. These are both major gas brands in
California.
Clearing the adaptation sounds interesting. I'll get the radio code from my dealer and try that.
...It is also possible that I'm just experiencing the existential
angst of learning to service an unfamiliar power train. I've owned 7 previous
RWD
Volvos, and only Volvos, since '83. Do all my own repairs and
maintenance. A 5 cylinder engine, auto transmision, and FWD give me the
heebie-jeebies. Besides, the darn engine is mounted SIDEWAYS!
Finally, it seems to me that a 5 cylinder 2.4 liter engine designed
by Porsche should go like a bat outta hell. Presently this car is faster
than my
'82 240 (286k miles!) but slower than my '86 740 non-turbo wagon.
That's just not right.
Hm. Sorry to grump. Thanks for the help.
--
Bruce
Caveat on Platinum Plugs
Email sent to OzBrick, Sept. 2003
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
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).