Engine Running Cold and Knocking


POSCarDriver
10-04-2010, 11:11 AM
A couple of days ago my car started making a consistent knocking sound on the highway. It only occurs when I push on the accelerator and when the RPM's go above 3k; usually on hills or the highway. I can feel the knocking on my foot when I have it on the accelerator, so I would assume it is coming from that general area. It hasn't gone away and may have even gotten worse. On top of that I have now noticed that the temperature gauge inside the car is showing the engine is running cold. What would cause this to happen? Any help is appreciated. Thanks.

david-b
10-04-2010, 12:56 PM
Welcome to AF!

Usually when running cold, the thermostat is not opening. I would check that out first and replace. Even if it still looks ok, I'd replace it. It's cheap anyways. Next, I would drain and flush the entire cooling system. Drain out the coolant, stick a hose in the thermostat housing, run the car with it on until the draining coolant is just water, and then refill properly. Make sure the heat all the way on and on full blast while doing this.

One winter I had a busted thermostat and the car would never warm up to full operating temp. Sucked because it was a cold winter, and the heater will only blow cold air because of it.

As far as the noise... not too sure. If you're feeling it in the pedal, it sounds like suspension work. Can you hear any noise when the engine is just idling?

Lastly, what year/model do you have?

POSCarDriver
10-04-2010, 01:20 PM
Welcome to AF!

Usually when running cold, the thermostat is not opening. I would check that out first and replace. Even if it still looks ok, I'd replace it. It's cheap anyways. Next, I would drain and flush the entire cooling system. Drain out the coolant, stick a hose in the thermostat housing, run the car with it on until the draining coolant is just water, and then refill properly. Make sure the heat all the way on and on full blast while doing this.

One winter I had a busted thermostat and the car would never warm up to full operating temp. Sucked because it was a cold winter, and the heater will only blow cold air because of it.

As far as the noise... not too sure. If you're feeling it in the pedal, it sounds like suspension work. Can you hear any noise when the engine is just idling?

Lastly, what year/model do you have?

Thanks for the reply. I do not hear any noise when the car is just idling. I only hear it when the car is working hard (ex. higher rpms, uphill driving, high speeds). It sounds almost like I'm constantly running over small bumps on the road. I don't know if it is actually located by the accelerator or not. I just know I can feel the knocking/tapping vibration on my foot when it occurs and it's usually when I break the 45 mph mark. I thought the two symptoms (engine running cold/knocking) may be related since they both occurred at the same time, but it could also be a coincidence. My car is a 1998 Mitsubishi Eclipse RS.

SilvrEclipse
10-04-2010, 03:09 PM
If the car is running cold the thermostat could be stuck open. If it was closed the car would overheat. It could also be the temp sensor for the gauge has gone bad.

As for the knocking does it make the sound when just free reving?

POSCarDriver
10-04-2010, 04:38 PM
If the car is running cold the thermostat could be stuck open. If it was closed the car would overheat. It could also be the temp sensor for the gauge has gone bad.

As for the knocking does it make the sound when just free reving?

No it is only making the sound when the car is actually driving.

SilvrEclipse
10-05-2010, 07:08 PM
Hopefully its not a spun bearing. Could drain the oil and check for metal shavings or it could be something loose on the motor or suspension area. Try and narrow the area down where its coming from if you can

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