Noise from engine compartment, need help diagnosing

[CakeBlazer]

02 Trailblazer, 4.2L 6 cylinder.

I'll keep this simple - the thermostat stuck shut causing the exhaust manifold to overheat so it cracked. This also brought with it a sound that sounded like an exhaust leak, which the local mechanic agreed with.

All parts that have been replaced since that event include the thermostat, fan clutch, exhaust manifold (including new gasket and donut seal), upstream O2 sensor, and VVT control solenoid (oil in the plug, only noticed it was bad because I pulled the plug in the process of getting the manifold out).

The thermostat was replaced before the manifold and we did a coolant flush at this point, BEFORE replacing the manifold. This seemed to affect the noise being made while the engine was running as it became noticeably quieter.

That said, even now with the manifold replaced we still have a sound that on its face seems to be an exhaust leak, but I've learned with this vehicle there can be about 50 different causes for the same problem. The noise can be heard any time the engine is running. It seems to come from the area around the exhaust manifold, or at least that side of the engine as it is not as loud on the other side. It can be heard from within the vehicle.

The sound is somewhat indistinct and hard to describe, it's like an on/off ticking sort of sound, but I'd hesitate to describe it as metallic. Any ideas? Does it still have a leak or maybe something else is going on like a bad lifter?

 

[Maverick6587]

Any check engine light or indicator lights on? Have you checked your radiator fluid since it was flushed to see if it has changed color since then? Since the engine got hot enough to crack the exhaust, I would be concerned about a blown head gasket as well.

While the engine is cold, you could spray some soapy water on the exhaust manifold, where it connects to the engine. Then start the engine and see if you see bubbles being created where you sprayed the soapy water. That would at least give you an idea if it is sealed or leaking to start with.

You could do a compression test to check for leaks in other locations/cylinders/valves. Then maybe a leak down test to see how severe the leak is, if you have any other leaks. If you don't have either of the tools to do the compression or leak down test, I believe most parts stores carry them as loaner tools and the task is fairly simple to do.

Videos for instructional guides. Eric the Car Guy always does a great job explaining troubleshooting processes.

 

[CakeBlazer]

Any check engine light or indicator lights on? Have you checked your radiator fluid since it was flushed to see if it has changed color since then? Since the engine got hot enough to crack the exhaust, I would be concerned about a blown head gasket as well.

While the engine is cold, you could spray some soapy water on the exhaust manifold, where it connects to the engine. Then start the engine and see if you see bubbles being created where you sprayed the soapy water. That would at least give you an idea if it is sealed or leaking to start with.

You could do a compression test to check for leaks in other locations/cylinders/valves. Then maybe a leak down test to see how severe the leak is, if you have any other leaks. If you don't have either of the tools to do the compression or leak down test, I believe most parts stores carry them as loaner tools and the task is fairly simple to do.

Videos for instructional guides. Eric the Car Guy always does a great job explaining troubleshooting processes.

No warning lights of any kind. Haven’t checked radiator fluid but the vehicle has barely been driven, we just ran it around a little (less than a mile) to see if anything else was wrong. Not driving it until we know what the problem is. Still, I’ll take a look.

Guess I need to check the head gasket, and of course check if the head itself is damaged.

 

[gmcman]

I'm assuming that the engine overheated? If so, how long did you drive it? How hot did the coolant get?

If you drove it for a while with it at or past 260 then as Maverick stated there could be a head gasket issue.

Can you post a video?

Did you retorque the exhaust manifold bolts?

 

[CakeBlazer]

It hit 260 and probably went over.

I don't have a torque wrench (yeah I know) so if you're asking "are the bolts torqued to GM spec?" the answer is probably no. They were tightened decently but fear of snapping off any of the bolt heads meant we didn't wrench on them that much.

 

[CakeBlazer]

I saw in a post on another forum that someone mentioned putting in Sea Foam through the brake booster line which will produce visible smoke in the exhaust system that can be used to visibly identify a leak. Viable idea?

 

[gmcman]

There is a torque spec and sequence for the exhaust manifold bolts.

I did get a little nervous a couple times but after a few bolts all was good. 18 foot pounds, in sequence, 3 times.

I'll look for pic unless someone has it.

 

[Maverick6587]

Exhaust manifold torque specs are listed below in the screenshot.



@CakeBlazer Sea Foam wouldn't hurt. I would do the Sea Foam and the soap and water. That way the soap bubbles will trap the smoke and you would more easily be able to see any leaks.

Harbor Freight has some cheap torque wrenches or you can rent them from a local parts store.

 

[pm789632147]

Any check engine light or indicator lights on? Have you checked your radiator fluid since it was flushed to see if it has changed color since then? Since the engine got hot enough to crack the exhaust, I would be concerned about a blown head gasket as well.

While the engine is cold, you could spray some soapy water on the exhaust manifold, where it connects to the engine. Then start the engine and see if you see bubbles being created where you sprayed the soapy water. That would at least give you an idea if it is sealed or leaking to start with.

You could do a compression test to check for leaks in other locations/cylinders/valves. Then maybe a leak down test to see how severe the leak is, if you have any other leaks. If you don't have either of the tools to do the compression or leak down test, I believe most parts stores carry them as loaner tools and the task is fairly simple to do.

Videos for instructional guides. Eric the Car Guy always does a great job explaining troubleshooting processes.

Yes Eric is very proceeded and sees to therly explains everything in detailed manor.

 

[TollKeeper]

Yes Eric is very proceeded and sees to therly explains everything in detailed manor.