Engine knocking while warm

Hey everyone,

 

Today I was driving home and about a mile from my house I noticed my engine was making a loud knocking noise that began at about 1500 rpms and continued to 3k and I assume beyond.

 

My car has been running great to this point and I am getting a consistent 23-25 mpg. Oil is mobil 1 5w30 with about 2500 miles on it.

 

I changed my coolant 3 days ago and have been checking my fluid before ever trip and keeping an eye on my temp gauge (car has never overheated or gotten warmer than it should according to the gauge).

 

When I parked I saw that my coolant overflow tank was low (but not empty, siphon hose still submerged, barely). When I looked under the car I saw a drip coming from the lower radiator hose where it connects to the thermostat housing. I immediately tightened the hose clamp and the leak stopped.

 

After letting the engine cool for a while, I added coolant to my radiator. In all I added about 1/4 to 1/3 of a standard bottle of 50/50 coolant.

 

So my question: could this knock somehow be related to running low coolant for a short amount of time, even though my car did not overheat?

 

99 Legacy GT 162,000 miles

So my question: could this knock somehow be related to running low coolant for a short amount of time, even though my car did not overheat?

probably not,

 

how old is the timing belt?

and the tensioner?

 

if it is rod knock,

unplugging the plug wire should make it go away, or at least greatly reduce it.

 

a mechanics stethoscope will help you isolate the noise location.

rod knock should be down the center line,

tensioner noise will be up front on the driver side.

I have a feeling its the timing belt tensioner as the noise seems to be louder on the driver's side.

I also removed the left and right timing belt covers and the belt seems to have more play/slack on the driver's side than the passenger.

 

Couldn't get the crank bolt off so I still cant be sure... Here is a vid

 

 

To get the crank bolt off you can jam a screwdriver in the access hole on either side of the engine and break it loose with a breaker bar. Or get a long breaker bar and rest the end on the frame or ground and blip the starter which also works great.

Well the noise went away as quickly and mysteriously as it appeared... I was driving to my local Subaru mechanic (askims auto), noise was super loud like yesterday and then it just disappeared in an instant..

 

Showed the mech the video I took of the problem and he said it sounded like a connecting rod but pointed out that usually when something like that fails it will stay broken.. as in its unusual for a noise like that to come and go.

Only other thing he could think of was a plugged oil passage causing oil starvation in some part of the engine that worked itself free on the way to his shop.

 

Verified the timing belt and tensioner were replaced 30k miles ago with the shop I bought the car from 3 years ago.

 

Weird.

 

Mine does the same thing, kina. Its still alive 40,000 later. Oil stabilizer is the best thing I can say, it will still knock like this but best you can do is put the best protection between the parts as you can. I run diesel rated oil and I'm going to start each oil change off with oil stabilizer replacing a quart of the oil, but I also have oil burning issues, stabilizer helps.