Just want to make damn sure I get this right. Higher octane doesnt necessarily mean the combustion temps will run hotter, in turn making the engine run hotter correct? It just has a higher flash point and will burn slower.. hence insurance against detonation.
It is totally coincidence that when I started running 96 octane my car has been running a hotter coolant temp. Mixing 96 with 93 actually. I am going to change the thermostat and make sure the radiator fins are clean. This is also after I have my dual oil coolers installed which originally lowered my coolant temps, but have raised my temp by the airintake filters lol. I am thinking it is just thermostat time which will be changed shortly. I still need to properly seal in and duct my radiator, but I would like to figure out why I started running a hotter temp all the sudden first. 5°c on average. Temp got up to 105 and I was like woooooh. Heavy traffic, very hot day but still she never did that. 100 was hottest I ever saw and usually around 88c.

 

Typically, unless there gasoline chemistry is altered by using unusual chemicals, higher-octane gasoline will normally burn cooler than lower octane gas. It also burns slower, as you said, which in effect slightly retards the combustion event, similar to retarding timing. Retarding timing has historically raised combustion-chamber and EGT's, and as a result, coolant temperatures.

However, having said this, this is not likely to cause what you're seeing. Maybe you're making more power as a result of a new tune? Or maybe the fans are not working correctly.

 

Thanks for the reply. The fans seem ok, however I will double check to make sure they turn on "high". I will be replacing thermostat. I had major oil loss resulting in oil EVERYWHERE. It is possible that the oil is in the rad fins which could hurt the heat transfer. I could flush the rad again too although it was just done a couple months ago. I would like to get this addressed quickly. I just got dual oil coolers for a reason.... having high coolant temps kind of defeats the purpose lol.

 

Dave, It's probably me, but I re-read this several times and still not following.

OP....or ambient conditions aren't the same. You even noted "very hot day" and "heavy traffic".
And 105 C. is where low-speed fans initiate with the stock thermoswitch. Not panic time, but it's why a lot of us changed it out for the S5 FC thermoswitch (96 C.)

 

I guess to make it clear I should say. In very hot and heavy traffic she never got over 100°c. My fans run off pfc set at 80°c. I put about 8-9 gal 96 octane no ethanol and drove home in hot heavy traffic for a bit. Then she hit 105°c on commander for the 1st time.

The only other time she went over over 95 with same ambient and traffic was after my oil spraying from hose incident when it hit 100°c a couple times on coolant. I have yet to clean all the oil out of every thing (as you can imagine it is a nightmare).

 

So the only time I hit 105°c was after 96 octane.... which the more I think the less it could be. It was less than 1/2 a tank. It is with premix and 93 octane. So even if it raised octane it probably wouldn't be over like 94 so I dont see how that could raise temp that much.
I need to clean the fins out again I guess with degreaser. The ac condenser also. It cos be blocking the flow to the rad.

 

I run around on almost pure 76 100oct and don't have heat issues in summer CA weather. I have dual oil coolers, ron davis radiator, lower temp fan switch. Never noticed overheating. Just give good following distance in traffic to get clear air in traffic (don't shove your nose up their tailpipe).

 

Back in the old days, a common result of severely retarded ignition timing was engine overheating. This is not likely here, but higher octane gas does burn slower and so in effect slightly retards flame propogation, leaving the exhaust gasses slightly hotter when they enter the exhaust system, similar to retarded ignition timing but not nearly as much.

The OP was asking if higher octane gas "could" make the engine run hotter, so I mentioned this effect. It's not likely to be the root cause here, just an interesting tidbit.

 

 

Pretty much.
Caffeine hasn't kicked in yet, but here is a shot of my commander and I am like pretty darn sure the fans pop on at 80.