Mk3 Cavalier Owners Club | Vauxhall Cavalier Dot Com

I have been reading an interesting thread on the VW van forum.

It is regarding running issues and heavy sooting up of Bosch spark plugs.

Historically I have tried to stick to OEM original fit parts for all my cars - funds permitting.
So Bosch have been an original equipment supplier to GM / Vauxhall / Opel for years - and to VW too.
Many parts I will only fit the Bosch brand due to inferior other makes.

Okay Rob, stop waffling, cut to the chase...

It would appear that Bosch obtain various spak plugs from Russian or French manufacturers.

It is reported that Russian supplied plugs are the ones to avoid.
Poor insulation quality, excessive sooting up and a service life of less than 3000 miles.
Tests between the plug tip and the metal body have shown resistance values between 10k ohms and 100k ohms.
The resistance should be infinite - open circuit.
Excessive sooting of the plug can make hot-starting very difficult. In extreme cases, the soot is so thick, that the car will not start at all whilst warm.
I have also heard of excessive burning of the rotor arm tip and a weak spark.

The French manufactured parts seem to work perfectly, and to have a much better service life.

So the obvious question - How will I know whether my plugs are Russian or French?

Firstly the Russisn plugs are often very "cheap" to buy.
Always an incentive on these needy cars.

I am told that the country of manufacture should be stamped / etched into the metal part of the plug.



The moral of this is... if your car appears to have any issues with starting and running within 3000 miles of fitting new Bosch plugs....

Check which plugs you have, and if they are the Russian items, swap them out first, before potentially wasting loads of money looking for a fault elsewhere.

I'd go NGK or champion if you doubt the bosch ones.

You do occasionally see "Genuine GM" plugs, but they seem to say Bosch in the blurb.

I used to buy AC Delco back in the day, which I believe has been Delphi for mega years.

I am not sure whether it used to be said that either Champion or NGK were "hotter" plugs.
Plug specifications and properties have probably changed a lot since I first took notice of articles in Car Mechanics magazine back in the mid-90s.

Either way - this is just a heads-up, to consider two basics ideas.

1 - Just because it is new, it does not mean that it is working.

2 - Even though it is a big brand, as with many companies, even Bosch can out-source from poor quality manufacturers.

There are lots of big names now supplying "reboxed parts" with items manufactured in places like China or Russia to keep costs down.

Euro Car Parts is one of the worst for supplying reboxed 'tat' on a regular basis.

Interesting! Not had any issues with plugs recently but will keep my eye out for that.

The number of the plug used to indicate how hot it was rated