Question about thermostat and plug heat range

[lovemysan2]

Okay, I have about 12k on my rebuild and all is going pretty good. I don't know the actual compression ration of my engine but I have the 9.5 to 1 pistons and the head was decked when I rebuilt.

I have noticed that when the engine is very warm I get spark knock. This happens when the temperature is elevated above the 170-180 deegree normal( AC on, slow traffic). And as long as I drive gingerly its not a problem. But this is a work truck and I use it to pull either my tools or mower. I run premium fuel 93octane.

Should I switch to a lower temperature thermostat. Motorsports sells a 148 deegree but its $60. Is there any truth to the rumor that a colder thermostat reduces fuel mileage?

Also. The FSM suggest the colder plugs plugs for extended highway running. There are some slight marks on the end of the plug itself I think that it may be the plug glowing. Also there is no carbon on the insulator its a nice amber color. Would it be also help with the spark knock to run a colder plug

[C-Kwik]

Knock can occur from many things. Heat is a factor, but it probably should not on 93 octane even with the temperature elevated somewhat. I'd suspect something else may be going on.

Is the mark you are seeing on the plug on only one plug or all of them?

Running a cooler thermostat and/or colder plug may get rid of the detonation but it will probably be more of a band-aid for something else that might be a problem.

[lovemysan2]

I'm gonna get a picture of the mark and its on all of them. I buy good gas and try to stay away from walmart and the grocery gas stations. I ran a gallon of 112 octane for the first 8 or so tanks and didn't have any problems with the knock. But of course every good thing has to come to an end. There are no codes in the computer as of now. And both 02 sensors are new.

What are some of your ideas I'm freshout and lost.

[lovemysan2]

See the attached pic of a 12k mile plug. Its a denso

[lovemysan2]

here's a 300 mile NGK and another 12k denso the color change on the electrode goes from amber to rust almost.