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Knocking sound at start up in cold weather

Who: 2003 Toyota 4Runner SR5 V8 AWD automatic

What: Engine knocking sound

Where: Omaha, NE

When: This happens when I first start my car, typically in temps around and below freezing, there is a slight knocking sound. It seems to be coming from the engine and is in synch with the running engine. Its not so bad in the Park position or the Neutral position. But very noticeable in the Drive and reverse position. Allowing the engine to “warm up” seems to solve the problem. I say this because I do not notice it after the engine has warmed up as indicated by the temp gauge on the dash. I do run 89 octane with 10% ethanol regularly, but have filled it up with 87 octane thinking the ethanol may be the problem. There is no difference. Could anyone assist as to the problem I may be experiencing?

Could you describe the knocking sound a little better, OK I know it is hard.  I have a hard time thinking of what it might be.  Most of the things that come to mind might be possible, but not very likely.  

 If the engine is knocking it could be the fuel.  But that would mean the fuel was too low of an octane.  What octane does Toyota say you should be using?  You might try a tank of high test.  If it is recommended for your car, it might not be as expensive as you think to use since you might be better mileage.

What you might have is an exhaust manifold leak. As the engine warms up the exhaust manifold expands and closes the leak.

How long since you have changed the oil and filter?

Is the sound more like a knocking sound or more like a tapping sound?

And, as waterboy asked–How often is the oil changed–both in terms of miles and in terms of elapsed time (months)?

Do you have the right oil in it? How about the correct oil filter? do an oil and filter change and see if it goes away. If it does not, waste no time in getting the oil pressure checked.

The manifold leak is a good guess. I wish we could listen to it.

Is the noise like a “tapping” screwdriver on a piece of metal or like a heavy hammer hitting a big, heavy chunk of wood? Maybe you could isolate the sound by listening to the enine upon start-up with the hood up, head close (careful!) to the engine. Top end? Middle? Bottom? Close to either exhaust manifold? Rocketman

Thank you for all the replys.

To give more detail on the 4Runner:
The manual say 87 is fine to use as fuel and can except up to 10% of a blend. It is standard practice in NE and IA to sell the 89 octane with a 10% blend of ethanol in it. Its actually 10 cents cheaper than the 87 octane.

The vehicle has 93,000 miles and gets an oil change every 5k to 7k miles which happens every 3-4 months. I drive a lot for work and I just do it when I can. Firestone consistently changes the oil with 5W30 GT-1 Synthetic Blend oil. I assume that is their brand oil.

The knocking sound is one that sounds more of a screwdriver hitting metal. Not a high pitch metal sound like a little kid hitting a pot pan. Its more of a mid pitch knock vs a deep sounding knock. Or a solid metal being hit with a screwdriver as opposed to a hollow one. It sounds as though it runs in synch with the engine. So the turn over of the knock is very fast as when a car is started.

The temp this morning was only 28 degrees. But, I DID pop the hood this AM. Again the sound readily happens on start up, and when the vehicle is put into drive or reverse. I barely noticed it, if at all, when put in neutral or park. So it was difficult to get out of the car in drive and listen, but the sound seemed to come from below the vehicle and not from under the hood. The sound was not as loud nor did it seem to last as long, and my guess is the difference in temp. The colder it is the more notice able the sound.

Update: Temp 44 degrees this a.m. Girlfriend started car for me and put into drive so i could be outside the car and listen. Knocking sound did happen, but quickly subsided, within 30 secs or so. It was very noticeable when first put into gear but quickly got less and less louder.

I will filler’ up with 91 on the next tank and report any feedback. Thank you again.

I will attempt to also get a sound bite of the sound.

Thanks Joe, I put together a detailed response to all at the bottom of this page.

I was curious if you had been able to verify or confirm you analysis with the additional information I added at the bottom of this thread?


more of a knocking sound. please see the updated comments I posted at the bottom of the thread. thank you for your help.

The knocking sound is one that sounds more of a screwdriver hitting metal

Without actually hearing it…the description sounds more like a valve clatter problem. This is usually caused by oil starvation. I’ve seen many vehicles with this problem that last for YEARS without any incident. Get it checked out to make sure it’s not something more serious. I also suggest you chage your oil a LOT more often then what you have been.

Since it goes away when the engine warms up I don’t think it’s spark knock. Spark knock (AKA pinging or pre-ignition) gets worse with rising temps and it doesn’t happen at idle unless timing is way off. Higher gas octane won’t help.

You said the sound comes from down low, so I don’t think it’s the valve train.

I think it’s the rod bearings, main bearings, or piston slap. Get the oil pressure measured with a gauge. Low oil pressure could make the bearings rattle.

Do you ever drive the engine hard before it’s warmed up? That could make your pistons get loose prematurely.