Hi, first of all this is my first post here so I just wanted to introduce myself really quick. I have a 95 Subaru Legacy and I just love it to death. It has about 87,000 miles on it and I'm hoping to get several more years out of it before getting a new subaru. I'm honestly not a car guy, so that's why I'm turning to this community for some advice.

 

Now to my problem, and I think it might be spark knock (if I'm using that term correctly). When I accelerate sometimes the engine will rattle a little, really hard to explain the noise. I live in Arizona and this only happens in the summer time and only during the day, at night the engine runs perfectly! By searching the internet and figuring out that spark knock happens only when the engine is under stress and especially when it's hot I'm fairly confident that's the problem. So basically my question is what do you guys (and gals hehe) think? Is it spark knock? And if so what options do I have to get it under control? Thanks in advance for any advice you might offer!!

I will assume that you are using the same grade of gasoline as in the past since octane that is too low (see owner's manual) will cause "pre-ignition" or "pinging".

Some of the more common causes and remedies I've come across in dealing with the condition:

Old spark plugs - change plugs

Carbon buildup on pistons/valves - do upper engine cleaning using products such as Seafoam sucked into the intake manifold and sprayed into the throttle body or a gas line engine cleaner added to the gas tank.

Knock sensor - change sensor

There are some other exotic possibilities that I am exploring as I have yet to solve my problem of "pinging".

Hope the simple fixes work for you.

I assume Arizona summer weather is kinda hot? Maybe you don't just need new spark plugs, but it might be a good idea to get some "colder" plugs. Colder means able to dissapate heat from the plug tip more quickly.

 

Don't know about other brands, but NGK numbers are higher for colder plugs. So, for instance standard plugs in my Impreza are labelled BKR5E-11. Chosing colder would mean running BKR6E-11.

 

If you still have the owners manual, it should list the NGK plug for your engine. Most of us here agree that NGK plugs work very well in Subaru engines.

 

Good luck!

 

 

(If you plan on replacing the plugs yourself, the Subaru toolkit does include a plug wrench. It even has a rubber ring in it to grip the plug and stop it dropping out. Take note that you need to remove the battery to gain access to plugs 2 and 4. In fact, number 4 usually needs the windscreen washer tank moved a bit too.

Apply a small amount of copper grease to the plug threads and DO not tighten them too hard.)