One heat grade colder spark plugs
 

If I understand correctly, the heat grade of a spark plug is a trade-off between keeping the plug hot to burn off deposits, and keeping it cool to avoid pre-detonation. Car manufacturers will bias this trade-off towards hot because it keeps the service interval longer. Whereas - we ecomodders - could bias this cooler because we don't want pre-detonation. Once the ECU detects pre-detonation (knock) the timing will be permanently retarded until the ECU is reset. Retarded timing means less power is extracted from the fuel, and so worse MPG.

The NGK website says Spark Plug Terms
"When making spark plug Heat Range changes, it is better to err on the side of too cold a plug. Running too cold a plug can only cause it to foul out, whereas running too hot a plug can cause severe engine damage."

So worst case, cooler plugs would just mean checking the plugs more often for fouling.

Will this work to improve MPG???

I don't know but your theory sounds good to me.

Not sure, but in my pickup the retard on the timing is only for a short period, basically once I lift up off of the throttle it resets.

If one is doing other things that tend to put an engine on the ragged edge of detonation like grille blocks, higher temp thermostats, nearly lugging it, etc., colder plugs may expand the envelope of what you can get away with.

This is done quite a bit in the tuner world, especially those who are tuning under boost and e85... typically they run chipped ECU's or complete FMU's so it's a lot easier to manage ignition timing.

That being said, those who don't have that option (due to emissions testing, budget, etc.) often "trick" the stock ECU in order to gain a few extra degrees of timing... myself included (emissions testing here requires OBD2 port plug in, so I can only run a piggyback)

If you're looking for that few degrees timing, the most common way is to retard the base timing, generally around 4 degrees from stock then reset the ecu (disconnect battery, turn ignition on, press brake pedal 10 times, let sit for a few min, works on most vehicles) and allow the ECU base-map to establish itself (usually around 100mi) and then set the timing to factory specs.

This will give you up to a 4 degree (ECU controlled) increase in timing throughout your load range without exceeding the max OEM timing advance... not sure what it is on your Toyota, but on my Acura it's around 45 degrees.

On the other hand, those of us who are good at DWL might need hotter plugs because we spend so much time at low power settings.

Just a thought....

...simple "verification" test is to pull a plug every so often and SEE if it's running hot (burnt) or cold (carboned up).

I guess I'll be the Guinea pig. My ranger is timed at 20*btdc with the stock plugs. What I can do is toss in 4 lower heat plugs, unplug the battery, and then get the timing with a timing light. Does that sound like a solid experiment? Or did I miss something? Ill do it this afternoon because now I'm curious. Also, should I go 1 heat range lower, or 2? Maybe 3? It's not my dd and I don't mind blowin it up (that would give me a reason to swap in a smaller motor)

maybe i missed it, but unplugging the battery won't do you much good. the computer constantly adjusts to whatever the conditions are. do you know if you have vacuum advance timing or electronic? with vacuum you may not see any benefit.

Hey BackroadBomber,
That's great that you are going to give it a try. I don't think you will see instant results with this, only under those limited set of circumstances when pre-detonation would occur. As has been pointed out, that is probably more likely if you have a grille block or other mods to keep the engine hot.

@KSA8907, disconnecting the battery is required after installing the new plugs to clear the ECU of those situations it has already learnt when pre-detonation occurred with the old plugs. i.e. to give it a fresh start and learn the new parameters.

It has coil packs there's no distributer so it's electric. The nice thing is that even though I have no manual control over the timing, ford kept the same harmonic balancer from the 80's so it still has timing marks

Press & hold "Alt", then type 0176, release Alt, to get a ° symbol, fwiw.

Alt Key Codes

Well I won't get to this until the weekend. My buddies truck broke down and he needed to borrow the ranger till payday Friday. But, remember how I said my ignition timing is 20* before TDC? Well, according to the Internet, it's supposed to be at 10*... Is this why I've been getting crap mileage? Also, what could cause this? (Same plugs as when I was getting close to 30mpg)

20 degrees at part load sounds like it's in the right range...I think?

Bosch Heat Range Conversion Chart, Has NGK, Denso, etc

https://www.boschsparkplugs.net/lear...nversion-chart

or From NGK
http://www.ngk.com/learning-center/a...nversion-chart

That's the best indicator. :thumbup:

If you do a lot of local driving, meaning short trips and often with the engine not up to operating temperature you will be better off with a hotter plug.

I think that is a pretty big assumption!

If you take this logic a step further, it would read something like this....

The spark plug engineer speaking, "yes, we decided with a longer insulator tip, as this will lengthen the service life of the 'service interval'. However, we are now getting complaints of engine detonation for those who like to drive full throttle on the Autobahn. Oh that's OK as we built in a lot of extra cost into the vehicle to cover warranty work, so we should be fine!!"

Now would we expect that the vehicle engineers would actually say this? I doubt it, as profit margins on cars are very tight, especially for small cars. The engineers will always select a plug insulator temperature that gives them a safety factor for drivers who abuse the vehicle.

Elongating the service interval would take a back seat to keeping an engine from melting down due to a too hot spark plug in there.

Jim.