Noisy in Summer Quiet in Winter: Why?

I have a 2002 4 cylinder Camry. In the summer, there is a loud rattling engine noise that goes away when the car warms up [I can’t take it to the mechanic to have a quickie diagnosis because the car is warm by the time I get there). The noise does not affect performance in any way. In the winter, the noise goes away. What gives?



Look for a small crack in the exhaust manifold or leak in the manifold gasket, though that doesn’t fit entirely b/c if that was it, it would be more likely to be noisy i winter (when the engine is colder, and all the metal contracts more).

What you can do is leave it with your mechanic overnight.

I thought about leaving it with the mechanic. But the car is running fine, the issue is more of a curious annoyance at this point. Because of this, I don’t want to spend a ton of $ having a mechanic run a bunch of diagnostics for no good reason. I posted here in the hope that this is not that unusual of a problem and someone would have a convincing explanation.


The exhaust manifold logic goes like this - if you have a tiny little crack or break someplace, it can be such that it will show only with a cold engine. The metal contracts, the crack opens enough to let out some exhaust and noise. When the engine gets hot, the metal expands and the crack closes up.

If you’d rather know something for sure, the next time you start it from cold engine, pop the hood and then go listen. A little piece of hose can help you pinpoint noises - one end in the ear, the other fished around where the noise seems to be. If you do this be careful of moving parts such as the fan or pulleys for the serpentine belt.

The thing that troubles me about this diagnosis is that the noise goes away in the winter. I had a crack manifold gasket on my S-15…never made a peep in the hot summer days when the engine was cold…but quite prominent in the dead of winter.

I’m with you there - it was all I had for an idea though.

The interesting thing about thermal expansion and contraction is that in unrestrained parts it happens “photographically”. Holes, dimensions, and cracks grow smaller as the part shrinks and larger as the part expands, just as they would in a photograph. In parts reatrained by other parts expansion and contraction can take unpredictable turns. This concept works wonders for bimettalic springs that straighten or bend with changes in temperature, but can have weird effects when unintended.

While an exhaust system crack or leak is a good possibility, and should be recognizable by carbon residue, there is one other idea that comes to mind. You have in your exhaust system a valved setup that allows warm air from the exhaust to warm the intake to the engine when it’s cold. Its there to reduce engine warm up time for reduction of emissions. You may want to look there.

But I have to say that the only real way to start is to pop the hood, stick your head under, and listen while it’s rattling. If you haven’t yet done this basic first step, I’d suggest you do. You may find out exactly what’s needed and save time and money.

A loose heat shield can be effected by temperature. Be it hot or cold. Bring it to a mechanic and leave it overnight positioned over a lift. Then when the engine is cold, the vehicle can be raised, started, and then inspected for a loose heat shield.


Good point. Heat shields rattling are so common. Why didn’t I think of that? I must be slipping. Mad Cow I suppose.

To the OP; if it is a loose heat shield it can be secured permanently with a large worm-type hose clamp from the local hardware store.