More problems with Bosch spark plugs

C

Chris142

Joined
Jun 5, 2003
Messages
30,131
Location
Apple Valley, California
I got tasked with putting plugs in an 08 BMW X5 with a V8 yesterday. No easy task. Book time is 3.5 hours.

I was extremely careful not to drop the new plugs down the tubes and damage them. I did not check the gap other than looking at them as they said pre gapped on the box.

Got it together and it ran terrible. Pulled the codes and then removed the #5 plug that was one that was now throwing a code for a miss fire.

Found this burned spot on the porcelain. I'm thinking it's cracked there and is jumping to ground there instead of of at the top.

The plugs had less than 1 minute run time on them . At this point I am ready to wash my hands of Bosch plugs all together

Thoughts?

IMG_20250509_164003940.webp
 
A guy over on the Hyundai Kona forums took out his engine by using Bosch plugs. Bosch said he did not torque the plugs correctly as they said the crush gasket was not crushed enough. It appeared to be crushed 80% of the way. The plugs were the right #. But that gave Bosch a way out. The new engine cost the owner $9,500 out of his pocket. If I remember right it dropped the porcelain and then everything dropped from there, all the shot peening in a hot mess of sparkplug guts. My plug of choice for the last 25 years has always been NGK and or HKS Racing Plugs (made by NGK for HKS) or Denso. Even though I have used Bosch many times in German cars. And then, on any turbo car I will only keep plugs for 30,000 miles.
 
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I had a Bosch plug blow out of the engine of my truck. But previous owner had them installed as I’d never use Bosch in a Japanese car. I will use Bosch in my old Beetle though as it’s German. I have nothing against Bosch plugs as long as it’s in a German car.
 
When I brought home my first car (1988 Grand Marquis with 5.0) I replaced the OEM plugs with a brand new set of Bosch platinum plugs. On the first long drive I noticed it had an occasional miss fire. I wrongly assumed it must need a set of plug wires, cap and rotor, etc. I went right through the ignition and the misfire persisted. Hot dose of injector cleaner, Seagram intake treatment, nothing helped. Finally I decided to try a set of different plugs - just a cheap set of Autolite plugs. The car ran amazing after that.

Nothing looked odd on the Bosch plugs I removed, but they definitely didn’t run good. Lesson learned for me - stick with OEM plugs, or at least something close.
 
Years ago Bosch was regarded as the epitome of quality in ignition parts including plugs.
That's apparently no longer the case.
I never had a problem with their parts, although I've used Denso or NGK for the past twenty years or so.
 
NGK / Denso for me in foreign cars. No issues with either.
Autolite plugs have always been great in my Ford trucks.
Oh yeah, AC/Delco in my GMC vehicles did well too.
Never used any Bosh plugs but have used their filters... air/oil.
 
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Zee09 said:
Everything Bosch is trash...
Failed everytime I used them in my VW. Even their expensive HVAC units are Chinese junk...
Click to expand...

Yeah, I'm not a Bosch fan. Don't like their spark plugs, o2 sensors, or wiper blades. Their "iBooster" electric brake booster in Volts/Bolts is known to make weird noises (although I never had a problem with it). I'm not saying all Bosch stuff is bad, but I think they stretch themself too thin and try to make too many different things.
 
Chris142 said:
I got tasked with putting plugs in an 08 BMW X5 with a V8 yesterday. No easy task. Book time is 3.5 hours.

I was extremely careful not to drop the new plugs down the tubes and damage them. I did not check the gap other than looking at them as they said pre gapped on the box.

Got it together and it ran terrible. Pulled the codes and then removed the #5 plug that was one that was now throwing a code for a miss fire.

Found this burned spot on the porcelain. I'm thinking it's cracked there and is jumping to ground there instead of of at the top.

The plugs had less than 1 minute run time on them . At this point I am ready to wash my hands of Bosch plugs all together

Thoughts?

View attachment 278391
Click to expand...
Wow bummer. I've always had great life expectancy and smooth running from Bosch double platinum plugs with the twin tips. Could be a fluke. Were any others an issue?
 
Rob_Roy said:
When I brought home my first car (1988 Grand Marquis with 5.0) I replaced the OEM plugs with a brand new set of Bosch platinum plugs. On the first long drive I noticed it had an occasional miss fire. I wrongly assumed it must need a set of plug wires, cap and rotor, etc. I went right through the ignition and the misfire persisted. Hot dose of injector cleaner, Seagram intake treatment, nothing helped. Finally I decided to try a set of different plugs - just a cheap set of Autolite plugs. The car ran amazing after that.

Nothing looked odd on the Bosch plugs I removed, but they definitely didn’t run good. Lesson learned for me - stick with OEM plugs, or at least something close.
Click to expand...
They may not indexed correctly. If the gap in the plug faces the cylinder wall, it will misfire. I learned that the hard way.
 
97prizm said:
Wow bummer. I've always had great life expectancy and smooth running from Bosch double platinum plugs with the twin tips. Could be a fluke. Were any others an issue?
Click to expand...
It has 2 misfire codes. I did not pull the other plug yet because it's the worst to access and the main reason for the 3.5 hr labor rate.
 
AZjeff said:
Are you going to beat book time replacing 2 bad plugs? This sounds like a guaranteed come-back job. :mad:
Click to expand...
I brought up the fact that the plugs I removed were ngk . After the issue I told them to get me the exact ngk# I pulled out. I'm going to replace all 8 with ngk on Monday .

Hopefully they will soon understand how cheaping out on parts cost more in the end.
 
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