It’s true that big rigs are typically built to take a beating and still run fairly well, no matter what make and model. Because of this, some semi-trucks are still safe to drive even when they’re at least a decade old. That is, if they’re taken care of and the owners remember to follow the recommended maintenance schedule and make sure to replace parts that are worn out or broken.

That’s why it’s important that you ask about such things when you buy a used truck, since how well it was taken care of will affect your final decision. Other things to consider include low mileage versus high mileage, the relative age of the truck, and any features you’re after. But since you’re dealing with a used truck, you need to be careful about pushing the limits too much. Here are a few things to look out for that will tell you your semi-truck is no longer safe to drive.

5 Signs Your Semi Truck is No Longer Safe to Drive

Lack of Engine Power

Truck engines are powerful, but even the sturdiest of engines will weaken over time. A lack of engine power can show up in several ways, such as the semi-truck not pulling the same way it used to. Or perhaps there’s something off about the engine’s sound, or the top speed isn’t what it was before. If you find any and all of these to be true, then it’s possible there’s been a loss of cylinder compression. Other causes of a weakening engine include old piston rings, head gasket, or valves. 

If a truck’s engine is significantly weaker than it used to be, then it follows that the truck itself won’t be up to its usual workload. The danger, then, comes from when drivers force the truck to work as much as used to, which can lead to accidents.

Excessive Exhaust

Exhaust is a normal part of truck operation, but sometimes there’s too much of it. Typically, wear and tear on pistol liners or problems with the steel ring will lead to more unburnt fuel and even smoke going into the crankcase. So fixing those problems often takes care of that particular exhaust problem. However, a point will come where even regular maintenance can’t fix the issue, and you’ll either see a lot of exhaust coming out of your truck, or the exhaust is too dark. 

When this happens, your engine isn’t as efficient as it used to be, which can in turn lead to a loss of engine power.

Unusual Engine Noises

It’s true that you can usually hear your engine, but the sound should be closer to a rumble or a hum. In that case, the engine sound usually fades into the background. That’s why you should pay attention if the truck’s engine sounds louder than it usually is,  or if there’s something else that’s different about it, such as a loud knocking that wasn’t there previously.

There are times where oil contamination or wrong combustion timing is to blame for the knocking sound. Damaged liner seals, piston skirts, and main bearings can also cause a similar knocking. 

Given that, it’s important that you get your semi-truck checked. That way, the mechanic can determine the cause and recommend a solution. Any major issues with the engine and it’s highly possible that your truck will no longer be safe to drive.

Hazardous Brakes

There’s no question that all vehicles should have working brakes, and that they’re among the first things a driver should check before heading out for the day. This is doubly important for big rigs, because a semi-truck barreling down the highway could deal more damage than a small sedan if the brakes give out. 

If you’ve noticed that you’re holding your breath every time you have to drive down a steep road, there’s something affecting your brakes. Constantly repairing the brakes will eventually become less cost-effective, and in that case, it’s best to retire the truck than continue using it, given how much of a safety hazard on wheels it could be at that point. The same goes for if you try and have the proper repairs done, but they seem to have no effect on how well the brakes work.

An Increase in Use of Oil and Gas

The older a truck is, the less fuel efficient it becomes and the faster it runs out of engine oil. Having to constantly top up your engine with gas by itself isn’t worrying; that along with having to add more engine oil in between oil changes, however, is a concern. Damaged fuel injectors can be replaced, but if an engine is so damaged that oil starts to leak or ends up being burned, that’s when you need to seriously consider retiring the semi-truck. 

These signs may show up now and then, but only one isn’t a big cause for concern, usually because proper repairs can fix the problem. But if there’s more than one sign at once, or you notice them in quick succession, especially if you’ve just been to a repair shop, that’s a different story altogether. 

Remember: if there’s something wrong with a part of the truck but it doesn’t interfere with how well it runs, such as the hydraulics on a dump truck malfunctioning, that’s not immediate cause to get the truck off the road. But if the problems have to do with its engine, brakes, or anything that helps ensure it can be driven safely, then risking a drive isn’t worth it and it’s high time to look for another truck.