Tea leaves and spark plugs...

Much like a fortune teller sees the past and future with used tea leaves, I have heard that a good mechanic can tell a lot about an engine from it's used spark plugs.

These spark plugs were used for about a year, what can you tell me about my engine? Yes it has 6 cylinders... :yelclap:

We can tell those spark plugs are no longer in your engine

Sorry, but I had to

98NWCherokee said:

We can tell those spark plugs are no longer in your engine

Sorry, but I had to

Click to expand...

Not necessarily true. They were NOT in the engine when the picture was taken certainly.

I'm going to have to make a couple of assumptions here:

1) The colour of the picture is fairly close to actual colour (I've tried to calibrate my LCD to be as close as possible.)

2) That the "reach" on those plugs is correct (it looks awfully long...)

Given those two, I'd say that they look a little pale - indicating that they may be one heat range "hotter" than they really should be running. Typically, the white porcelain insulator will turn more of a "bone" colour due to deposits almost-but-not-quite burning off in use. If they stay white, you're running a plug that is too hot - which can lead to cracking of the porcelain insulator and HV leakage between the centre electrode and metal shell.

I do see some small dark deposits (probably carbon) on #2, #4, #5, #6 (from left) which is fairly normal, and nothing I'd worry about.

Try stepping one heat range cooler - if you are running hot with your plugs, it will help with spark plug longevity. Make sure your reach is correct (that could be a later model - and I think they did use a longer reach on those. I'm used to RENIX engines...) and the rest should be okeh.

Tips for future reference:

1) Take the picture against a known white background - printer paper works well. It's a better colour reference than cement or workbench. Use a Sharpie pen in black, blue, or red to make any marks on the paper needed - and be sure to mention what colour you use. Not everyone's monitor is properly calibrated for colour, and elimination of assumptions goes a long way...

2) Number the plugs, or have them in order and tell us which is #1. Often, imbalance problems or head gasket problems can be partially identified by reading plugs, and it will help to know which one went where.

3) Make sure to give vehicle specifics in your post - year/make/model (I assume you have more than one vehicle, yes?) mileage, and whether you think there is an issue or not. If there is, we can help you find it. If there isn't, you'll be happy to have been proven wrong, and you'll probably learn something in the meantime.

If you check most Chilton's guides on the shelf at your local, you'll find that an awful lot of them have one full-colour glossy page in them, and that's the spark plug key. If you find it, take the time to study it - you can get confirmation from the rest of us, but you'll have a better idea of what we're looking at as well...

Don't deride reading plugs by compairing it to Tea Leaf reading.

Your engine is not burning oil.
Your Engine is not running rich.
It does not appear to be detonating (ping).

All good so far

Ideally the electrode should have a very light brown coating. I don't see that in your photo. That leads me to believe the engine is running slightly lean, or you have too hot a plug installed.

Is this a STOCK motor, or a Stoker?

-Ron

Excellent information, thank you. I purposely was vague as I didn't want to taint the fortune, ahhh, information.

I'm going to have to make a couple of assumptions here:

1) The colour of the picture is fairly close to actual colour (I've tried to calibrate my LCD to be as close as possible.)

I believe the color to be very close to the original colors of the plugs.

2) That the "reach" on those plugs is correct (it looks awfully long...)

I'm not sure, I told them at the parts place the make, model, blah blah of the vehicle. No telling what they are really for, perhaps they are even the correct ones.

Given those two, I'd say that they look a little pale - indicating that they may be one heat range "hotter" than they really should be running. Typically, the white porcelain insulator will turn more of a "bone" colour due to deposits almost-but-not-quite burning off in use. If they stay white, you're running a plug that is too hot - which can lead to cracking of the porcelain insulator and HV leakage between the centre electrode and metal shell.

I do see some small dark deposits (probably carbon) on #2, #4, #5, #6 (from left) which is fairly normal, and nothing I'd worry about.

Try stepping one heat range cooler - if you are running hot with your plugs, it will help with spark plug longevity. Make sure your reach is correct (that could be a later model - and I think they did use a longer reach on those. I'm used to RENIX engines...) and the rest should be okeh.

Tips for future reference:

1) Take the picture against a known white background - printer paper works well. It's a better colour reference than cement or workbench. Use a Sharpie pen in black, blue, or red to make any marks on the paper needed - and be sure to mention what colour you use. Not everyone's monitor is properly calibrated for colour, and elimination of assumptions goes a long way...

Good idea.

2) Number the plugs, or have them in order and tell us which is #1. Often, imbalance problems or head gasket problems can be partially identified by reading plugs, and it will help to know which one went where.

They are in 1 to 6 order left to right.

3) Make sure to give vehicle specifics in your post - year/make/model (I assume you have more than one vehicle, yes?) mileage, and whether you think there is an issue or not. If there is, we can help you find it. If there isn't, you'll be happy to have been proven wrong, and you'll probably learn something in the meantime.

1998/Jeep/Cherokee (NOT GRAND!) 150k total mileage, 10k estimate on these plugs. I have a mpg and a running hot issue. Someone saw this picture and thought the 4.0L may be running lean. I'm thinking that if this is true I may have the answer to both my mpg and running hot issues.
It runs 210 40 mph- and well over 210 at 65 mph. Getting close to the hash mark after the 210.

If you check most Chilton's guides on the shelf at your local, you'll find that an awful lot of them have one full-colour glossy page in them, and that's the spark plug key. If you find it, take the time to study it - you can get confirmation from the rest of us, but you'll have a better idea of what we're looking at as well...

Great, I did a search hoping I'd find one online before I posted here.

Checking plugs when over heating for smelly, wet ect. Also a bad idle and a loss of coolant would indicate coolant getting into the cylinder(s)
Plug look clean and you didn't list a loss of coolant. So no on the head and/or gasket IMO.
Over heating at speed tends to indicate a lack of air or coolant movment. AT 64 MPH fans are almost unnesseryanf would be the last thing I would look at. So if the rad fins are not cloged/covered by something I would look to coolant flow problems.
Tstat do go bad and are cheep and easy to change. So why not change it.
Rads: Not cheep but a common problem. Look very close at it. OK (IMO) flushing a clogged rad is a wast of time and money. Flushing should be done to keep it from clogging when some of the cleaner can still get throu the tube. Once a tube is closed there is no flow so no cleaning.
Lower rad hose collapses.
To test hose. Warm engine to operating temp. REV engine up and hold it. Watch hose. IF it collapses? Replace.
Water pump impellers do rust away but not often and if anti was always used in the coolant that was changed from time to time. Very seldom.
The block/head could just have a ton of gunk buildup. Onces again seldoms happen with good maintaince.
luck

badron said:

Checking plugs when over heating for smelly, wet ect. Also a bad idle and a loss of coolant would indicate coolant getting into the cylinder(s)
Plug look clean and you didn't list a loss of coolant. So no on the head and/or gasket IMO.
Over heating at speed tends to indicate a lack of air or coolant movment. AT 64 MPH fans are almost unnesseryanf would be the last thing I would look at. So if the rad fins are not cloged/covered by something I would look to coolant flow problems.
Tstat do go bad and are cheep and easy to change. So why not change it.
Rads: Not cheep but a common problem. Look very close at it. OK (IMO) flushing a clogged rad is a wast of time and money. Flushing should be done to keep it from clogging when some of the cleaner can still get throu the tube. Once a tube is closed there is no flow so no cleaning.
Lower rad hose collapses.
To test hose. Warm engine to operating temp. REV engine up and hold it. Watch hose. IF it collapses? Replace.
Water pump impellers do rust away but not often and if anti was always used in the coolant that was changed from time to time. Very seldom.
The block/head could just have a ton of gunk buildup. Onces again seldoms happen with good maintaince.
luck

Click to expand...

No coolant loss. CFS 3 core, hoses, t-stat, water pump last year. New lower hose didn't come with a spring, but I used the spring from the old one. I still need to check for collapse.


mmmm looks yummy!

This is at least a year old coolant.

Zuki-Ron said:

Don't deride reading plugs by compairing it to Tea Leaf reading.

Your engine is not burning oil.
Your Engine is not running rich.
It does not appear to be detonating (ping).

All good so far

Ideally the electrode should have a very light brown coating. I don't see that in your photo. That leads me to believe the engine is running slightly lean, or you have too hot a plug installed.

Is this a STOCK motor, or a Stoker?

-Ron

Click to expand...

No insult to anyone that can "read" spark plugs, but since I don't know how to do it, it seems like magic to me.

This is a stock 1998 Jeep 4.0l engine. I (and my wife) are the only owner and driver's.

Well I don't have the box for the plugs any longer, but here is a full shot of one of them. They are Champion but they are a more expensive plug. I broke one of these taking them out, so I replaced all 6 with the Champion el cheapos ($1.99 each).

Here's a chart http://opc.mr2oc.com/online_parts_catalog/emissions/spark_plugs.jpg

The problem with these charts are that they only seem to show plugs with an extreme version of the condition they are showing. Reading plugs is like conducting a black box experiment You have no idea what is actually going on inside the box, just the condition of the plugs before and after the plugs have been subjected to the box. You make a hypothosis and back it up with more experiments on the box (vacuum checks, compression checks...).

150K and some other slight cooling/MPG issues. Hmmmm.

Some things which made a difference on my Jeep. Maybe look at some of these.

Clutch Fan. Mine was locked up, yours may be the opposite. Either way is bad as a locked fan will cause the engine to work more at cruise.

Vacuum leak. The connection to the bottle was bad, and causing a lean condition.

Make sure the AC condenser is clean as that will certainly generate more heat if clogged.

Cat. I noticed a 2-3 MPG increase when I changed out my cat around 145K.

-Ron

Mudderoy said:

Much like a fortune teller sees the past and future with used tea leaves, I have heard that a good mechanic can tell a lot about an engine from it's used spark plugs.

These spark plugs were used for about a year, what can you tell me about my engine? Yes it has 6 cylinders... :yelclap:

Click to expand...

Honestly, all I see are a set of plugs that were pulled around 20K miles too early. Try looking elsewhere for your overheating concern.

I know you said the radiator was new, but it could be restricted. Get your engine fully warmed up, then drive it around the block. Once you get back shut the engine off and use your hand to feel for any cold spots on the radiator. If it is hot all over, then you can officially eliminate the radiator.