Regarding a 2018 3.5L EcoB (SCrew 4x4), what is the gap for replacement spark plugs. On RockAuto, there are several different products available but they have different gaps. Is there a resource to help me decide which plugs to purchase?

See snippet below for the options.

 

Set the gap to 0.028"-0.030". I run a 5 Star 87 p/t tune so mine are set at 0.028".

 

Owner's manual says gap 0.030" - 0.033".

Vehicles typically also had it on the emissions sticker under the hood but haven't looked at mine honestly.

 

owners manual states .030-.033

I agree with the above and set mine .028-.030. You can find them pre-gapped. I would use motorcraft plugs...5 star tuning sells the ford perf motorcraft plugs pre-gapped and they are usually cheaper

 

Use the SP 594 Plugs at the 031 Gap. Your base known and tested Plug for the engine application.
The other offering are Gaps related to the plug Tip Metals >Erosion rates< used, in the deign trying to equal or extend plug life.
All different plug offerings and mfgers are NOT exactly the same for Heat ranges and metals used in their Tips.
Boosted engines are harder on Plug Tips than NA engines and taken into account for Metals used, and Gap life in this application.
It shows when Gaps for 5 L NA are compared to 2.7 /3.5 L ECO engines. Big difference.
When you change plug mfgers, you take a chance on plug life and performance under a hope they would be equal or better.
A stock engine does not need an upgrade for normal average use.
.
Living example:
I found this out by my trial on a 5L.
Plug listed for this engine turned out to be too HOT in Heat range, and resulted in all the Gaps went wide to cause misfires and had to be replaced at low mileage.
Took a lot of plug research to find this all out besides visual plug condition when removed and also monitored with a Scanner checking Mode 6 misfires records for all cylinders.
The hint was geee, these plugs look too >>clean and porcelains too white, along with wide gaps at 060+. Wonder why!?
A mistake picking off a list of other mfgers.

Good luck.

 

also will stay with the SP594, and their .031 gap. I will double check them.

 

always check the gap! You don't know how the plug was handled before you bought it. All plugs can be adjusted. Just have to know how to do it.

 

ironically, the amount of replies some of these gap questions get responded to with “just smack it on the table to close the gap” followed by, “oh gee, no idea why I’m getting a miss” I’d think most should stick with the pre-gapped plugs and just check them.

but, never meant to imply to not check them, just stating that you can get them gapped properly from a few sources