2004 Isuzu Ascender makes "fan" noise when accelerating

this make and model is the same as a Chevy Trailblazer

It has 124K miles on it

when it’s cruising, there is no weird noise from the engine, but when I give it gas at any speed, there is a distinct sound coming from the rear of the engine. It sounds like when you put a playing card on your bike and the spokes hit it, but faster. the more gas, the louder the sound. It’s gotten progressively worse lately.

My first thought was rattling valves, but I’m not sure. It also sounds like a hole in a vacuum hose or something. With the hood up and an ear to the engine, the sound is definitely coming from the engine, not around it, and toward the rear.

Any ideas?

Is it coming from the same side as the exhaust manifold? If so, it could be a leak in the exhaust manifold gasket. My old Buick Skylard had the same noise under acceleration and it was the gasket.

I believe it’s possible to burn a valve if the leak is not repaired. One of the old hands can correct me if I wrong.

Ed B.

from the inside of the car, it sounds like it’s coming from behind the dash on the passenger side, so that would be the exhaust manifold side, and from the engine with the hood up it’s coming from the back of the engine… again, that seems to match.

so, price wise, any thoughts on the cost? I’ve replaced manifold gaskets on other cars, but only during a major tear-down kind of job. If I have a mechanic do the job, I’m wondering how long this would take?

This car is starting to cost a few hundred every few months… my warning flags are up