What are my plugs telling me?

[Grover]

Attached are two photos of my Bosch W8DC plugs which have been in for about 1,000miles. Some parts of the plugs seem to have the nice tan/gray coloration, but others suggest possibly a too rich mixture? Also, I noticed that on the plugs from cylinders 3 and 4 there is a wet oily residue quite a way up the threads vs. on the plugs from cylinders 1 and 2 (this is what the second photo is trying to illustrate, but not very successfully.) I'm doing this exercise to help me diagnose some oil burning, but I don't see signs of that on these plugs. Am I correct? Thanks in advance.

[alp]

isn't it very difficult to read plugs with unleaded fuels? I thought that it was a "lost" art nowadays because of the change to unleaded.

[jgerry2002]

No, you can still read plugs. Not sure where you heard that unleaded fuel changes this.

The plugs look a little rich, or if you've done a few short runs without the motor fully warming up then the plugs can look like that too.

Edit: they don't look that oily to me, but I'd say your car is burning a little.

What is the oil consumption like?

[Grover]

I'm burning quite a bit of oil, probably in the range of a quart every 750 miles or so. The head is recently rebuilt but is still showing some of the same signs as prior to the rebuild. I'm just trying to look at every indicator possible to help in diagnosing what's causing the problem.

[jgerry2002]

1 quart per 750 miles is a lot.

What are your compression numbers? What about a leakdown test?

Both of these should give you your answer.

[Beaner7102]

The best way to read plugs it to go for a good 20mile drive, then find a nice flat straight section of road, with the engine at high revs 3-4k turn the key off, brake and pull off the road. Then pull the plugs and read them. Otherwise you will get a false reading from slowing down to an idle (rich running?). Beaner7102

[Guest Anonymous]

Nicely stated, Beaner!

[Grover]

I don't know the compression numbers and I've not done a leakdown since putting on the new head. I'm considering taking it in to have a new leakdown done next week. And thanks for the advice on how to get an accurate reading, I'll give that a shot this weekend and see what difference it makes. While I've got some people's attention, on top of the intake manifold there are two small points/needles sticking up that have little rubber "caps" on them, they're just on the intakes that lead to cylinders 1 and 4 and are about half way between the carb and the head. What are these?

[Guest Anonymous]

I think they may have been for emissions stuff. I have mine plugged since I removed all mine. Other than that I can't tell you anything...steve

[TobyB]

Maybe. If you're burning that much on long trips, I agree.

If it's mostly stop- start and short trips, I wouldn't get too worried-

it'll burn more with the engine cold, usually... especially if your rings are

getting older.

t