I might be wrong here but I noticed something that surprised me this week. I usually run the 89 octane fuel as that is my best choice at the local station. I am about 2000 feet above sea level so it isnt an issue usually. Last weekend I had a misfire code at idle so when I gassed up I put in a jug of Lucas octane booster.

Now my running temps have dropped from 188.6 to 183.2. Same weather. Same trips. Am I crazy here?

 

I don't know how octane boosters raise the octane number of fuel,
But I know that higher octane fuel's straight from pump have lower calories as they burn compared to lower octane fuel's, so they actually make less heat.
(Higher octane is less combustible fuel compared to lower octane, that's why it's used in higher compression engines), for same reason if someone uses higher octane gas in an engine that is designed for regular fuel the engine will feel a little weaker,

 

Just FYI all octane boosters are a sham. I've done the math before and even if the bottle of stuff were like 300 octane, the amount of fluid it adds wouldn't increase the octane by even a whole point. This has also been shown my numerous independent dyno tests.

So, no. The octane booster didn't change your running temp. Could've been changes in wind speed, cloud cover, following distance or the aerodynamic properties of the vehicle you're following, leaves or something blocking your radiator, something breaking loose somewhere in your coolant path; a number of things.

That is quite a drastic change though. It could be related to the misfire at idle you experienced at the same time. Were it me I'd give the whole truck a good once over and watch the sensor live data for a while if you have the ability.

 

I'm pretty sure that 89 octane is never the "best choice" at any gas station.

Due to the ECU being tuned to run your high compression engine based on 92 octane you are actually costing yourself more money and getting less mileage by using cheap gas.

Keep in mind you are operating a $40K vehicle. No matter what you may have paid for it used. You have to treat and maintain it as such. Else it will keep costing you more and more.

 

These engines are not high compression.
The high octane requirement is because they have no EGR valve.

 

Some places way up in the mountains it is because you don't need as high of an octane at higher altitudes.

 

They are kinda. They run 11:1 or 12:1 compression which is quite a bit higher than most NA V8s on the market.

 

I didn't know that.
I thought they were 10 to 1

 

From the RAVE:

Compression ratio:
⇒ Low - 4.0 litre 8.23:1
⇒ High - 4.0 and 4.6 litre 9.35:1

 

Sounds much more realistic