Hot weather = engine knock

[LearjetMinako]

So for the past month and longer, I have been frying under the sun. It has been a constant 100*F days since before July. I think we are on a track record of 40+ days in the 100's degrees. One of the things that I noticed with the 96' Ranger 2.3L engine is that my little engine rattle is coming back. Which last time I found out is the engine pinging from high loads on the interstate. A spark plug swap fixed that issue. But now with the very hot weather, I noticed it the other day going 45mph down Sooner Rd.. And the engine wasn't even under a heavy load. Just put a little more throttle into it and the engine starts rattling a little. So this fill-up I'm going with 91 octane fuel till it cools off for the winter.

I guess the question I should be asking is that is it nesseracy to use a higher octane fuel with hotter weather conditions? I know the higher octane won't hurt anything besides my wallet. But better my wallet than a hole through the piston later.

 

[daniel3507]

Ive noticed the same thing. I havent tried higher octane yet but I might see if it helps any since there is no end in sight for the weather. 110 today and possibly even hotter tomorrow.

 

[straycat]

Hmmmm, maybe check the timming?? I never had that problem here inFlorida with any of newer cars or trucks. Years ago when I had my street / drag hot rods I would notice that issue on really hot days. I just played with the timming a bit and that resolved the issue. Don't know it that will help but it can't hurt to try it.

 

[LearjetMinako]

Florida has humidity in the air. Which helps as an anti-knock agent. Here, it has been 110*F with 9% to 20% humidity. All my timings are correct.

I have filled up with 91 octane straight gasoline, so far so good. I haven't notice any knocking so far.

 

[straycat]

I gased up with 87 octane this morning and it is $3.49 as of today. What are you paying for 91 octane there? I wouild rather see you tinker with the timming than pay a lot for gas just to keep the motor from pinging. What plugs to you run?

 

[LearjetMinako]

I paid $3.79 for the 91 octane. Timing on my Ranger is non-adjustable, except for the cam timing belt. I could probably switch back once the hottest days only reach in the 90's instead of 100's. Which by the way, it got up to 114*F yesterday (8/2/11) and 110's are starting to become the norm. Going to work at midnight it was 94*F.

 

[Musick17]

Illinois is 100+ degrees with 80+ % humidity
walk outside and you feel wet

 

[adsm08]

If you are running 87 now (which you should be) try 89 first. If that doesn't do it then try 91.

The extreme temps could certainly cause your issue, but with the age of your truck there is probably something else going on too. Carbon deposits on the face of a valve or the top of a piston will get hotter and stay hotter than clean metal and can cause knock, which will be more prominent in extreme high temps.

Switch to the next grade up for your next tank of fuel and run some Lucas and/or Seafoam through it to try and get the carbon out.

If that doesn't work an induction system service may be in order. There are expensive ways to do it and there are cheap ways to do it. If done right both can be effective.

 

[country0001]

Have you tried thicker oil?

 

[LearjetMinako]

I don't think thicker oil would resolve the issue. I already use Royal Purple 5w-30, which is a full synthetic oil.

As for carbon deposits, don't think that is the issue either. I just recently ran E20 fuel for a whole a tank. So the ethonal should have really cleaned up the inside of the engine. And I always run a can of B-12 Chemtool every oil change to clean the fuel system every 5k miles, except this time because of the E20 fuel. And I just recently, less than 300 miles ago, changed the oil.

As I stated in a previous post, the 91 octane has seemed to resolve the knock issue. Also, I didn't mention this yet, the engine is not overheating. So thats not an issue either. The engine runs at 190*F till it gets over 110*F outside and then it runs a little hotter, but never exceed 200*F, yet.