The last thing anyone wants to hear is a strange noise coming from the engine while driving. Hearing anything out of ordinary usually means there’s an issue with the car. If you hear a knocking noise from the engine, it can mean that you’re in for a potentially expensive repair. Why? Because one of the possible causes is rod knock and that means tearing down the engine.

Something similar happened to us. After seeing the oil pressure warning light come on, it didn’t take much time to hear the horrific sound of the rod knock. The worst thing is that it happened only a week after the 9-5 Aero was back on the road. Unfortunately, it’s a common issue for the early pre 03 Saab 9-5, and it was something to be expected.

Article updated on 12/06/21. Original publishing date 05/03/16

What is Rod Knock?

Although knocking from the engine means there’s a serious issue going on, not all knocks are rod knock. It’s important to know the difference, but to do so, it’s necessary to know what a rod knock is.

Rod knock is the sound you hear when one or more rods hit against the crank. The knocking increases in both sound and intensity as you accelerate, and decreases when you start slowing down. Unfortunately, this isn’t a 100% accurate symptom, so as soon as you hear any type of noise coming from the engine bay, make sure to check it out.

Rod knock is an issue that occurs when bearings on connecting rods wear, allowing more movement of the pistons that causes metal-on-metal contact. In most cases, the knocking sound gradually increases as the bearing wears, but it can happen instantly as well. The latter occurs when you spin a bearing due to a lack of lubrication.

Why Is Rod Knock So Common In Early Saab 9-5 (03 and Older)?

One of the reasons why rod knock is so common in the pre 03 Saab 9-5 is because of an engineering fault, so to say. Saab was a Swedish car company, and because it’s located in one of the coldest parts of the world, the engineers thought it would be a good idea to place the catalytic converter right below the oil pan.

When it comes to driving during the winter, it’s actually a good solution to getting the engine warmer in less time. However, the additional heat from the catalytic converter creates an issue with the engine oil any other time of the year — sludge. Oil sludge was a problem for early gen Saab 9-5s while this problem tracks back to Saab 900/9000 models as well.

The issue was partially fixed by switching to fully synthetic engine oil. However, if regular maintenance wasn’t done on time, rod knock would rear its ugly head again.

How to Troubleshoot Rod Knock

When you hear a knocking sound from the engine, it’s not always rod knock in question. A few other car issues have a similar sounding symptom which includes:

• Bad main crankshaft bearings
• Bad timing belt tensioner
• Bad AC compressor
• Broken flywheel or flex-plate
• Sticking valves
• Bad water pump bearing
• Bad alternator rotor bearings

Because so many other issues can cause a similar sound, it’s important to tow your car to an experienced mechanic who will properly diagnose the knocking sound. On the other hand, if you have experience in working on cars, and you’re not afraid to get down and dirty, there are a few things you can do to check if you have a rod knock or any other problem.

Check What You Can Before Opening Up The Engine

The thing about a knocking noise coming from the engine bay is that it doesn’t necessarily mean it’s coming from inside the engine. Many people go through a lot of work only to find that a complete engine rebuild didn’t resolve the knocking noise.

There are a couple of things you can check with little to no disassembling involved. We’ve mentioned some of the most common causes for a knocking noise, so you should start from there.

If you don’t have proof of when the belts, tensioners, and water pump were replaced, it’s best to inspect those components first. Even though it’s recommended to replace all these wearable parts as soon as you buy a car, a lot of people skip this step to avoid the extra costs.

Visually check the condition of all the belts and try to move the tensioners by hand. If you notice any play, you should replace these parts right away because it’s just a matter of time when the play will become worse and cause serious damage to the engine. The alternator, water pump, and AC compressor are the most common parts that should be replaced.

Checking crankshaft bearings, the flywheel, and valves should be the next step if replacing the suspicious parts didn’t resolve the issue. This will require a bit more work, but it must be done in order to resolve the knocking issue. If you’re not sure how to do this, it’s best to leave it to a certified professional.

The following steps will show you what to do and what to look for if the above tips didn’t help you resolve the knocking sound, and you’re certain the car has rod knock.

Remove The Valve Cover And Look For Sludge

Because we know that rod knock is a common issue on the early Saab 9-5, the first thing we did was to remove the valve cover looking for sludge. In our case, that wasn’t the problem, so we continued looking for the cause of the knocking by checking the oil pickup tube.

Because the oil pickup tube has a very small strainer, it’s common for debris to pile up and limit the oil flow significantly that can lead to rod knock and other serious issues with the engine.

Check What Caused The Excess Debris

A common practice for mechanics and self-taught enthusiasts is to use anaerobic sealant with the rubber valve cover gasket. The thing about the early Saab 9-5 is that there’s no mention of using the anaerobic sealant, but the previous owner, or their mechanic, used it.

Although anaerobic sealant is usually a great choice to completely prevent oil leaks, in our case, it caused the engine to develop rod knock. The sealant shouldn’t harden outside the gasket area, but because of the heat, oil, and the fact that too much was used, it did harden and the debris got caught in the oil pickup tube’s strainer.

After inspecting the oil pan as well, there were a lot of chunks of the hardened sealant and rod bearing.

Always Follow Manufacturer’s Instructions

A lot of serious damage to cars is caused by fitting inappropriate parts and ignoring the service intervals recommended by the manufacturer. In the case of our Saab 9-5, an anaerobic sealant, that shouldn’t be used, caused the rod knock that required a full engine rebuild to fix.

Even though errors happen, the engineers know the car they produced inside out, and which parts need to go in the car to make it work properly, and when they need to be replaced for regular maintenance. That’s why it’s recommended to replace parts included in regular maintenance as soon as you buy a used car, especially if you don’t know the service history or whether OEM parts were used.

The Place To Find OEM Parts For Your European Car

Whether you own a BMW, Audi, or the same Saab 9-5 we just talked about, eEuroparts.com has the parts and kits you’ll need to perform quality regular maintenance.

The beauty of these maintenance kits is that they include every single part you’ll need, from recommended engine oil, filters, gaskets, to the smallest nuts and bolts. All you need to do is select your specific car and find the parts you need. It’s a simple process, and you’ll always get parts that fit perfectly on your car.