[RAV4EVR]

My engine had started to knock a little during acceleration at 181k miles. I have a stick shift. I tried to switch gears at higher speeds but it was still there so I decided to do what I did in college with my 300k mile 1988 Honda Accord. I switched from 87 to 93 after emptying my whole tank.

The RAV knock is all gone. Very smooth quiet acceleration. Good 180 degree noticable difference.

Just wanted to share my experience for those who are in the same boat.

I have read all articles possible on octane usages for the last 100 years !!

Nowhere I saw it written down that switching old engine to a higher octane will take knocking away... (in those words) ..
With a big trip coming up this was a good relief.. phew !

 

[ajkl]

Carbon can build up inside the combustion chamber, raising the compression ratio, which then pre-ignites when using low octane gas, which is the pinging sound. Higher octane gas resists pre-ignition, resolving the pinging issue.

 

[RAV4outnbout]

My engine had started to knock a little during acceleration at 181k miles. I have a stick shift. I tried to switch gears at higher speeds but it was still there so I decided to do what I did in college with my 300k mile 1988 Honda Accord. I switched from 87 to 93 after emptying my whole tank.

The RAV knock is all gone. Very smooth quiet acceleration. Good 180 degree noticable difference.

Just wanted to share my experience for those who are in the same boat.

I have read all articles possible on octane usages for the last 100 years !!

Nowhere I saw it written down that switching old engine to a higher octane will take knocking away... (in those words) ..
With a big trip coming up this was a good relief.. phew !

Thank you for posting! I'm starting to get a very brief knock when I first hit the throttle after shifting or when accelerating from a stop...I'll have to try this tomorrow when I fill up!

 

[RAV4EVR]

Thank you for posting! I'm starting to get a very brief knock when I first hit the throttle after shifting or when accelerating from a stop...I'll have to try this tomorrow when I fill up!

Make sure you empty the tank completely first which is what I did.
Let us know.

I am going to try to put the buildup cleaner in my gas soon to see how it fixes my issue and if I can go back to 87 sometime soon otherwise I will try to continue using 93.

 

[leon r]

Try using combustion chamber cleaners. It does requires removing the spark plugs to spray it in, but they do work.

 

[pico]

Nowhere I saw it written down that switching old engine to a higher octane will take knocking away... (in those words)

I'm surprised because it is well known. I've used high-octane in some old cars such as a bored and stroked VW Type 1. Some configurations with squish pistons and semi-hemi heads don't need it.

Some knocking on old engines comes from carbon build-up which increases compression and sometimes also 'hot spots' of carbon. One way to clean pre-cat engines is to rev it way up while pouring diesel fuel down the carb. It will also get rid of mosquitoes. Lots of smoke. (It is amazing how much diesel will pour through a revving gas engine.)

 

[leon r]

Well, it is know that high octane gas will reduce knock on high mileage engines, but... this is a Band-Aid approach, the real solution is to get rid of carbon deposits.

 

[pico]

Well, it is know that high octane gas will reduce knock on high mileage engines, but... this is a Band-Aid approach, the real solution is to get rid of carbon deposits.

It was so easy to remove the heads on my old Harley Shovelhead. During the Winter, we would pull the heads and soak them in pail of WD40. Over three months it reduced the carbon to fine sand, easily washed out and ready to go for good weather.

 

[RAV4EVR]

Well, it is know that high octane gas will reduce knock on high mileage engines, but... this is a Band-Aid approach, the real solution is to get rid of carbon deposits.

Agree. I will work on that once I return from the West IF my RAV4 is able to make it back from a 6000 some mile trip from the mountains.. LOL !

Since I burn a quart a 1000 miles, may be a replacement engine?

 

[twinn]

Well, it is know that high octane gas will reduce knock on high mileage engines, but... this is a Band-Aid approach, the real solution is to get rid of carbon deposits.

Seafoam does a good job of removing carbon in the heads. Pour it in your tank and you will notice the difference.

 

[RAV4EVR]

Seafoam does a good job of removing carbon in the heads. Pour it in your tank and you will notice the difference.

Did it BUT before a 6000 mile trip across USA. Was that stupid?
Freaking out. I poured it and then thought of consequences. What if my fuel filter or something gets clogged with broken pieces. I am F****D !

 

[twinn]

Seafoam will break up the carbon so that it burns and exits through the exhaust. It will not clog the fuel system and will treat the fuel to remove water and other contaminates. Your worries are not a problem. Drive safely.

 

[Beaumont67]

Seafoam will break up the carbon so that it burns and exits through the exhaust. It will not clog the fuel system and will treat the fuel to remove water and other contaminates. Your worries are not a problem. Drive safely.

^^ Agree.

Fuel made with corn, is 15% Ethanol...now a days here.
The small engine shops, were first to discover the deterioration in the entire fuel delivery system...in lawn mowers, wipper snippers, snow blowers, etc.

^^ SeaFoam solves the problem with inferior corn gas blend.
Every time I fill up a Jerry Can, Seafoam gets added to treat & stabilize the gas.
Case in point:
- my Stihl FS85 trimmer is 20 years old, never been serviced & starts easy
- my Honda track drive snow blower is 20 years old, never been serviced & starts easy
- my garden tractor with mower is a John Deere GT262 (made in 1998) and still runs perfect
- my garden tractor with snow blower is a John Deere 318 (made in 1992) and still runs perfect
I run a few ounce of SeaFoam, in my suv's & truck filled gas tank, once a year...the stuff helps and is proven automotive safe.
- also Company has big branding, in the boating world / marine SeaFoam, is even higher strength