Should I use a colder plug?

[Jerome74911S]

Not a major topic and I've posted similar questions before, but still, I want the engine to run properly.

Here's the odd part, this affects only the number two cylinder. The others run clean. This plug has hard carbon on it - not oil - and also an over-all glaze that suggests a too-hot plug. The coating chips off with difficulty in hard flakes.

Is this a reasonable diagnosis (too hot)? Why only the number two plug?

[manbridge 74]

With today's RFG I'd say stock or one step hotter.

Maybe #2 has some oil seeping by the guides.

[thumbdoctor]

Looks OK to me. Safe with a little bit of deposits. I'd stay with that heat range unless there's some fouling issues with #2 cylinder. The best way to evaluate engine condition is to perform a plug chop. Clean (new) plugs, run the engine to high RPM and cut the ignition then coast to a stop. Pull the plugs and see what colour / deposits you have.

[Reiver]

Lots of 'modern fuels' leave a coating like that ...some more, others less. They make it harder to read plugs than in the leaded days.
I'd go with what you have, looks like you are getting more oil in that chamber than the others but it is far from fouled.
As the T Doc says you are reading your idle presently, the only way to read a plug is as he described...at load then engine off.

[Jerome74911S]

Originally Posted by Reiver

. . . As the T Doc says you are reading your idle presently, the only way to read a plug is as he described...at load then engine off.

Thank you. Yes I know. The thing is that the coating on that one plug is so hard that it's difficult to scrape off, so I have a hard time to imagine that it would blow off with hard running, nor that it would build up so fast on a new plug tested as described.

Maybe I'm too much of a worrier over little things, but it's just odd. In the first picture the entire end of the plug has an even brittle coating on it which looks smooth in that photo.

[scarceller]

I'd say #2 is running hot with some oil burning. Keep in mind that hot could also be caused by #2 cyl running lean. Be sure you don't have an air leak at the gasket to the intake port at the head. If it's CIS injection check the spray pattern of the injector on #2 by pulling the injector and having it spray into a can and comparing that injector to say #1 injector.

One more thing that can cause a plug to heat is a cracked, chipped or improperly seated exhaust valve. I'd do a quick compression test on all cylinders.

Also if #2 plug looks significantly different than the others that's a key indicator something is up! So you are not just a worrier! You should investigate why, you are doing the right thing.

[nickyclyde]

How long does it take for a new plug to get looking like that?

[Jdub]

My post of a few months back might be of interest. I also have one plug that shows symptoms of bad oil control ring/valve issues.

Also, to the question of how long - if you roll to the end of my thread you can have a look at what a plug looks like after ~1K from the cylinder I describe above. Have to dig out the PPI to find the comp and leakdowns when I bought it.

[Jerome74911S]

Originally Posted by Jdub

My post of a few months back might be of interest. . .

Yes, it was, thanks. I installed a new injector on the cylinder that causes the plug fouling. No change. So, time to look at the easiest things first, i.e. vacuum leak, followed by compression test, etc.

Nuts. I ran a jug of Techron through it a little while ago. No change with that attempt, either.

[T77911S]

i would look at fuel volume out of all 6 injectors. compare to each other.

you could have air leaks on 4 cylinders making 2 run rich.

what plugs are in there?

i dont think #2 is too hot. it also depends on how the engine was shut down. long idle can make the plug look richer.

i did a lot of research on plugs a long time ago. what i found out is for every plug there is a different opinion on how to read it. but one site said the line on the ground strap should timing. look at your last pic. the line where it goes from grey to black is an indication of proper timing, according to one or more sites i read.

the porcelain should be whiter. but if you are not fouling, i would not go hotter. the main purpose of a hot plug is to keep from fouling at idle and startup. if you just drove on the hiway and never had to drive around town, you could run a bosch W4 or even 3. i know, i did it. i tested a W4 in my 77. around town the plug was black. i took a 500 mile trip and pulled my plugs, they were clean. even after being used in my brothers 930. they were actually grey, but that is how i got them, but no soot or any deposits.

you did not say what year the car is. a CIS car may have dirtier plugs than an EFI car.

[thumbdoctor]

Worst case scenario would be:
1) Valve guide seal brittle and leaking (can be replaced in car)
2) Valve guide irregularly worn (Top end job)
3) Bad ring or ring land damage from detonation (carbon deposits build up increasing the compression ratio and then it feeds on itself)

A leak down test will tell you more about the condition of your engine. If you only have a compression gauge, perform a cold compression test followed by a warm one. Another issue about compression tests with CIS is to disable the fuel pump and hold the air vane open and throttle valve wide open to obtain maximum volumetric efficiency while cranking.

[thumbdoctor]

The silver ring on the ground electrode method of reading spark plugs seems to be more effective at reading carburetor jetting on small engines and two stroke cycle engines. I have written many blogs on this subject for snowmobile/motorcycle sites. In all honesty, I don't think you have a big concern with this cylinder. As stated, there are many different kinds of carbon deposits that present themselves on today's spark plugs. I've had orange coloured deposits show on race car plugs (using race gas). After speaking with with the nice folks at VP fuels, it was discovered that one of they're blend additives contained red dye.

[scarceller]

What I look for in plugs is how they look compared to each other, this tells a lot about how the cylinders relate to each other. A plug that's significantly different than the others deserves some level of investigation. Would be nice to see a picture of all 6 plugs together.

[T77911S]

+1
i am more concerned with how they look compared to each other. you have 2 that you say are dirtier than the others. i would find out why. at you least you are on the safe side. when you have ONE that is much cleaner or whiter than the others, then you risk damage to that cyclinder.

[Jerome74911S]

Thanks for all the great ideas and advice, guys. At the moment my back is "out" and I'm walking around bent over, so I'll have to hold off any fooling around with the car for the time being.

However, to answer some questions: I have one plug only that looks suspicious, which is the one in my original post. The other five all look like the one pictured below. I take the little white spots to be deposits from some fuel additive. The plugs are Bosch WR-5-DC+.

The engine is from a '75S and it has its original CIS. The engine was rebuilt with all the usual upgrades and this was done in the relatively recent past, but this issue has developed just this summer. As I mentioned above, I replaced the injector in that cylinder (#2), but this made no difference to the deposits subsequently appearing on the one plug seen in the first post.

It takes about 1k miles for the overall ceramic-like deposit to develop, again as seen in the first post.

Here's what the other five plugs look like. BTW, the engine originally NGK plugs that were colder. I'll try to see if I have a record of what they were, although the current issue did not exist then.

[T77911S]

that plug looks fine for a CIS engine.

W5 was what i ended up using in my 77s.

like i said earlier. i would do a fuel volume comparison of all 6 injectors. just put all 6 in seperate containers, turn the key on and lift the sensor plate for about 30 seconds, depending on the size of the containers. the more fuel, the better the test.

then i would look for air leaks on the other 4 cylinders.

i found a bad fuel liine on one of my injectors. its was only allowing half the fuel as the others.
this problem had been going on for at least 2 previous owners.

[manbridge 74]

What is your timing set at 6000 rpm?

[Reiver]

It does appear that one pot is running leaner. That plug has almost normal deposits/wear on one side and the 'hot' side in the second pic. You are not getting even combustion from a lean AFR.
Either a limited fuel issue or an air leak somewhere.

[Jerome74911S]

Originally Posted by Reiver

It does appear that one pot is running leaner. That plug has almost normal deposits/wear on one side and the 'hot' side in the second pic. You are not getting even combustion from a lean AFR.
Either a limited fuel issue or an air leak somewhere.

More likely an air leak, as the engine tends to run rich overall. Are you referring with these comments to the picture just above, or the original 2 pictures of the same plug in the original post?

[HawgRyder]

When I was running a drag car (427 Ford Fairlane) I ended up with 3 different manufacturers of plugs...in a couple of different heat ranges.
It made about 2/10's of a second better times with that combo.
I know...a V8...but the basic principal is the same....use what works for you!
Every engine has hotter and cooler running cylinders...it's the cooling system that causes that.
If you put slightly cooler plugs in a hot running cylinder...and hotter plugs in a better cooled one....the result is a smoother running engine.
There are many people that will deride this idea...but in my experience...you do what needs to be done to get the job done.
Bob