Whats up guys , I'm getting a knocking sound when I start the car . It sounds like it's coming from behind the right side of the radio. It's somewhat loud , it only last like 20 seconds then goes away. Only happens when I start it , any ideas ?... It's a 02 cl-s

 

I'm getting the same thing...it's weird...I think it has to do with the AC, because i dont even start the engine and its knocking then goes away.

Also, it only does that sound if my temperature knob is all the way to the left (cold)...if it's knocking, turn the knob to halfway or all the way hot and it'll stop.

 

Could be the rear motor mount.

 

I have navi tho ?

 

it's something to do with the air though.

without A/C, fan or the engine on, i turn the temp knob and it stops.

...I did just replace the cabin filters a couple weeks before that, did you?...if i have time i'm gonna take them out again and take a look to see if everythings put back correctly...

 

Happens to me sometimes. I think its the heater core valve or whatever controls the air temp that comes through the vent. I just ignore it now.

 

Theres possibly a bit of air in the cooling system. Once the car warms up a bit, the fluid and air bubbles are cycled back to the radiator and bled out slightly.

 

Are you sure you're using 91 octane per manufacture specs?

 

Generally when you have a knocking of a cold engine on start-up the two things you consider first are rod-knocks and piston-pin knocks. Rod knocks are caused by excessive clearance between the connecting rod bearing and the crank journal, piston-pin knocks are cause by excessive piston pin hole wear in one or more of the pistons. Both sounds go away as oil pressure comes up or engine parts, particularly pistons, warm up and expand and you won't hear them again until you start the engine cold. Both problems will eventually lead to engine failure, often catastrophic engine failure.

Of course it could be just your heater, but keep this in mind. You have a thermostat in there somewhere and as long as its working there is no movement of coolant at all in your heating system until the temperature comes up - which certainly does not happen when you start a cold engine. So no matter what it is that is causing your noise you can bet the farm that it is not in your heating system. As for the notion that it may be low octane fuel, well, that one doesn't wash either. In order to get an ignition knock you have to have resistance against the movement of the pistons and you can't do that sitting there in neutral just revving the engine, it has to be in gear and moving the car to get the sound of a pre-ignition (or detonation-induced) knock out of it.

At any rate it could be all sorts of things, but you should start by looking at the ones that have the potential to do you the most harm or cost you the most money first, and then move on to the problems you hope are the cause because they are either cheap to fix or easy to ignore.

 

Anyone ever find out what the cause of this problem was ? my step mom just called me and she's having this issue with her 2000 CL type s. She said the first couple times it happened it lasted for 30-40 seconds but now it lasts for 10-15 secs then goes away. Car seems to be running OK. I have not heard or observed for myself as she lives a couple hours away.
Thanks

 

Won't cause knocking, ECM will retard timing accordingly based upon unput from knock sensor. edit: he has older car so premium not required and no knock sensor

OP check your front motor mounts, my car makes a clunk when i put it in reverse and that is becuase the front mount is toast. I am going to do the front and side mount this summer. Rear mount should be find as it is rarely stressed but I can replace it if needed

 

Forgot I got this checked out at the dealership. They said its the door that swings open to control hot and cold air. It was stuck and wouldn't open/close all the way so thats the sound of it trying to open/close. They said it was like 1400 to fix I said no, and the guy said "I don't blame you". I forgot all the technical terms he used, hopefully you understand my description.

 

My a/c vent door started knocking just as you described. I can feel the door knocking inside the housing just to the right of the console and under the radio. The dealer price to fix it for $1400 is ridculous,they probably want to replace the entire dash and inner vents. Someone here must have repaired the problem. The main issue would be access to the vent door. My guess a plastic piece broke inside and is preventing the door from opening. The door is trying to open so the vacuum mechanism is working. I assume it is vacuum operated, it may be an electric motor, does anyone know how the door is actuated? I can't ignore the sound, it's too annoying, besides if it's broken, it has to be fixed. Your help is appreciated guys.

 

most of that $1400 is labor to remove the dashboard;. The dash has to come out in order to replace the housing for the HVAC

 

I found some helpful information on the TL forum. There is a good possibility that the motor is the problem. I was able to locate the motor, it is in the center of the dash just to the right of the console. There is an external rod goes in to the housing. I was able to see the motor jerking the lever, while making that clicking sound. I was able to pull the lever to one side, which stopped the jerking. I assume the door is either now shut or open all the way. Then I lubricated the lever and some of the connections with silicone spray. So far today it has not been knocking. There is a part of the housing that appears to be easily removable, clip on one side and two screws near the firewall. This may be the housing for the heater core. If I continue to have the problem I will remove the cover to see if I can view the area where noise is originating. The problem could still be the motor. It is of a flat configuration and may have gears inside that actuate the lever that could be damaged. The motor is very easy to remove and if it requires replacement costs about $115. It may be worth your while to get underneath to see if your problem is similar to the one I am having. I'll keep you posted if my problem persists and I investigate further.

 

Since my last post the knocking stopped on it's own. When it turned cool outside I found out I had no heat. As it turned out the problem was the actuator motor, under the dash and to the right of the console. The part was about $150, online, and a half hour to install. Climate control works perfectly.

 

Did you have to take apart the dash or can you access it right from the front passenger area?