Spark Plugs; Mileage
 

For my 1989 L4 LE with 144k miles, can I use platinum or iridium spark plugs, or must I use OEMs? The engine idles a little rough (nothing new since I bought it three months ago). Platinums cost me only $1-$2 more than copper, so price isn't an issue.

Despite the deep spark plug hole, changing spark plugs is not a problem for me, and I use anti-seize on the threads and customarily remove them every 5-10k miles to prevent them from freezing in the engine and to evaluate the engine condition.

What is the current thinking for how often to change spark plugs?

What are the criteria for replacing them, or is there a mileage limit?

Also, should I put dielectric grease on the spark plug tip that connects to the spark plug wires?

Thanks as always!

You can use any type of plug.

The original plug was NGK BCPR5EY11 and ND Q16R-U11. Factory recommended interval change period was 30K miles or 36 months.

Can use platinum, double platinum or iridium. Don't try to gap these types of plugs.

As a plug wears, the electrode gap increases. To a point, this increases the voltage needed to discharge the electricity across this gap.

The criteria for change can include continuing to emissions standards, MPG and performance. Performance such as ease of starting, acceleration, smooth idle and no misfire. This assumes the engine is running OK. Not burning excess oil, fuel, etc. which would affect the electrode and cause premature problems.

Rather then have the owner guess at all the above and when to change the plug. The manufacturer makes a recommendation based on miles and months.

Dielectric grease can help keep out moisture and ease boot removal.

The V6 option specified platinum plugs changed at 60K miles or 72 months.

Thanks for your reply.

How much improvement in gas mileage, if any, would I get from using my current copper plugs to platinum and/or iridium plugs?

Thanks

Most likely none. The issue is "copper" degrades faster which can lower MPG.

The term copper is illusive. Most plugs have a copper core, its the electrode material that varies. Copper plug electrodes are not copper but nickle, nickle plated or something else.

Iridium and platinum electrodes last longer and can be designed differently. The issue is these plugs last longer.