Can I Drive Without A Serpentine Belt? – don’t do it!


A broken belt is a pain in the ass, no doubt, and a tow truck can be expensive and then there’s the waiting, I get it, I’m a mechanic. But please don’t drive your vehicle without the belt the risks of serious engine damage is pretty much guaranteed. A belt costs a few dollars, a new engine, thousands.

Most vehicles do not use a serpentine belt to drive the engines coolant pump, driving such a vehicle without the serpentine belt is possible, but not advised. If however, your vehicles coolant pump is driven by the serpentine belt, driving without the belt will overheat and damage the engine. The serpentine belt on all vehicles drives power for the electrical system and likely also powers the power steering and air conditioning systems.

In this post you’ll learn why driving your vehicle without a serpentine is a really bad idea. You’ll learn what’s at risk by doing so and you’ll also learn how you can fit a serpentine belt at home.

What Happens If I Drive Without A Serpentine Belt?

The serpentine belt is a super important component on your engine, this seemingly unimpressive belt carries a lot of responsibility, as you’ll find out.

You’re considering driving without the belt, I understand, breaking down is inconvenient. Ok, here’s the deal. Cars need coolant to continuously circulate the engine, they employ a pump to move the coolant, the pump, known as the coolant or water pump, is driven by a belt.

For the purpose of this post we’ll divide engines into two camps, those that use a serpentine belt to drive the coolant pump, and those that don’t. The difference is unbelievably important if you’re considering driving your car with a busted serpentine belt.

Coolant Pump Not Driven By Serpentine Belt

Most modern cars coolant pumps are not driven by the serpentine belt. So in theory you can drive a modern vehicle with a busted belt. But wow…not so fast, we’ll need to check a fact is a fact, just because your car is modern doesn’t mean it’s safe to drive. And even then, driving such a vehicle is not without issues, but more on that later.

Some may run a dedicated second belt for the water pump

You’ll need to identify which type setup you have, make sense?

Pop the hood and check for a black plastic cover, it’s a good indication the engine is belt timed and therefore coolant pump is not likely driven by the serpentine belt. Many modern cars utilize the engines timing belt (concealed internal belt) to drive the coolant pump and so won’t be visible.

Timing belt cover

Ok, you think your pump is not driven by the serpentine belt, so what other issues need you be concerned with? See below “What a serpentine belt drives” for a better idea of how it affects your cars performance.

Coolant Pump Is Driven By Serpentine Belt

Serpentine belts are sometimes referred to as drive belts, Auxiliary belts or just Aux belts. Some cars (mostly older vehicles) use a drive belt to drive the coolant pump. On older vehicles, it was known as a fan belt.

The absence of a plastic cover on the engine suggests it’s a chain driven engine and so increases the chances the coolant pump is driven (externally) by the serpentine belt.

Chain driven engine
CP – Coolant Pump CS – Crankshaft A – Alternator PS – Power Steering I – Idler

As you’re debating if you should drive without it, we’d better look at what’s at stake?

And it’s a S*%T ton. If your engine cooling pump is driven by the serpentine belt, driving without the belt looks something like this:

  • Engine will start fine but you’ll have a red battery warning light illuminated on dash board
  • Vehicle will move not problem but the steering will feel heavy
  • The vehicle air con won’t work and the button may display a fault warning
  • After the vehicle warms up, weather dependent but usually ten minutes or so, you’ll notice the temperature gauge climb above normal but car still drives ok
  • Temperature gauge now in the red, car smells funny, engine may begin to sound unusual, and overheating warning light on
  • The car may stall at this stage and you get the big screen moment – steam from under the hood

The engine may restart fine after the it cools, or it may not. Your battery is charged by the alternator which is driven by the serpentine belt. The battery may now be too low to start the engine.

If the engine does start, it may become apparent that there’s a problem. Head gasket failure is highly likely. Some tell tale signs are – white smoke from the exhaust, excessive pressure in the coolant system, fresh coolant dripping from the vehicle, erratic idling

Now we need a tow truck, and thousands of dollars to fix it.

What A Serpentine Belt Drives

Serpentine belts are also known as auxiliary or as fan belts. Serpentine is an apt name as the belt does resemble a snake as it wraps around various pulleys at the front of the engine. The name fan belt isn’t used as much anymore, modern cars use electric fans, no longer belt driven.

We’ve covered what happens to a serpentine belt driven coolant pump vehicle. So you’re up to speed on that one.

All the systems listed below, are likely driven by the serpentine belt and will affect all vehicles, no matter how your coolant pump is driven.

Power Steering

Pulley id

Your vehicle likely has power assisted steering, most do today. Latest technology cars use electric steering and so initially you won’t be effected by the lack of a serpentine belt. I say initially because your serpentine belt also provides voltage to run the power steering, and when that runs out you’ll feel how a non power assisted steering feels – heavy.

Although electric assisted steering is popular, so to is the traditional hydraulic assisted steering. It employs a pump driven by, you guessed it, the serpentine belt. So if your vehicle has hydraulic power steering it will feel heavy with out the belt.

As your steering is mechanical, it still works and at higher speeds will feel pretty normal, just feels very heavy at slower speeds.

Alternator

The alternator makes all the power your vehicles demands, and modern vehicles demand a ton, because everything is electric. A cars battery is not designed to run your electrical system, it’s function is instead to store energy and keep control module memory powered until you restart your vehicle, the next day or whenever.

It’s the alternators job to produce all the energy your vehicle demands (when engine running), it does this in an instant with the aid of computers.

As the alternator is driven by the serpentine belt, your alternator isn’t producing voltage. And as your car uses voltage to run, fuel pumps, ignition systems, control modules, electric steering etc. it will quickly deplete the battery, likely within an hour or so and now you are stranded.

Power Brakes

Most vehicles use a brake booster and engine vacuum to help apply the vehicle brakes with ease. However, some larger vehicles may employ hydraulic power steering pressure to apply the brakes, and since you know how the power steering pump is powered, you’ll also know vehicles with this type brake booster will suffer from ineffective brakes.

Trying to drive a vehicle without a working brake booster is dangerous and not advised.

Air Conditioner

And of course the air-conditioning pump is powered by the serpentine belt and so the A/C won’t work. It’s a minor inconvenience and since the battery will be flat soon, it won’t much matter.

How To Replace A Serpentine Belt

Belts come in two flavors, those that are tensioned with a spring loaded tensioner and those that are known as stretch fit.

Most however are tensioner fit and that’s a good thing, stretch fit can be challenging in confined engine bays. That said some serpentine belts fitted to large engines can be tricky to fit also. I won’t use the word hard, as the mission itself is relatively easy, completing the mission with a lack of real estate, that’s what tests your metal.

Before you get started, here’s a few tips. If you were replacing the belt, first make a diagram of how it’s routed, you may think you’ll remember but if there’s a ton of pulleys, it’s easy to get lost. A picture works too, but often can’t get all the pulleys in the shot.

Of course if your belt has broken, you won’t have any clue as to how it’s routed, trial and error works but if the belt is an awkward to fit, once is enough to do it, right?

A quick google of your vehicle serp belt routing or YouTube are the two best resources of info. As belt replacing is common, there’ll be lots of info.

Anyhow, here’s an outline of what each belt type fitting process looks like.

Tensioner

Most vehicles won’t require covers or shield removed in order to fit belts. However the larger the engine generally speaking, the more challenging the job is, and so expect and allow for a cover or two.

Tensioner

You’ll know a tensioner type as there’ll be a spring loaded tensioner arm. Tensioner arm generally incorporates a feature that allows for easy manipulation. On many it’s a fixed hex head that allows the technician fit a low profile socket and ratchet. Pulling on the ratchet releases tension from the serp belt and with your free hand remove the old belt from the tensioner idler pulley. Pull the remainder of the belt free.

The fitting process is as follows:

  • If you have the old belt, check the new belt is correct diameter and number of ribs
  • Fit the new belt starting with the crankshaft and using your diagram or picture as reference
  • Finish at the tensioner idler
  • Using the socket and ratchet, tension the arm and fit belt onto the idler pulley (don’t place fingers between pulley and belt – not fun)
  • Release the ratchet and check carefully that all belt ribs are sitting in all pulley grooves correctly. If not, release tension again and with free hand, push ribbed belt into its seat.

That’s it, your work is complete.

Stretch fit

Stretch fit belt

Stretch fit generally aren’t very large belts and are fitted to smaller engines with less pulleys so you could say in that sense they are easier. The challenge with these belts, is the lack of space (usually) and the nature of stretch belts mean the engine needs to be cranked over by hand in order to fit the belt.

Take note of the belt routing if your belt is still in place. If not google or You tube is your best source for routing.

So you’ll need a long ratchet and socket fitted to the crank pulley (harmonic balancer), removing the spark plugs will make cranking by hand easier.

In colder temperatures especially, the new belt can be a pig to handle, you know, stiff and uncooperative. If so, boil some water and submerge the belt a while to soften and expand it a little, makes quite the difference.

If your belt is still in place, use a knife or loose hacksaw blade to cut through the old one. No going back now!

Cutting off stretch fit belt

A new belt kit usually incorporates a belt fitting tool (looks like a shoe), if not, don’t panic, fitting is still possible. We’ll do it both ways.

The vehicle will need to be in Neutral (N) and ignition off with parking brake applied, it’s important as we’ll be turning over the engine. A vehicle transmission in gear or in park (P) will prevent engine rotation.

Fitting the new belt with the tool looks like this:

  • Use hot water to soften the belt
  • Fit belt to all pulleys and finish at the crank pulley (Harmonic balancer)
  • Have crank socket and ratchet and belt tool to hand, now offer the belt to the right hand side of the crank pulley
  • Place the shoe between the belt and pulley
  • Turn the crank clockwise while your free hand aligns tool and belt on the crank pulley (long handle ratchet makes it easier as to does removing spark plugs)
  • Continue to rotate the crankshaft until the belt is seated, remove the tool
  • Check the belt ribs are seated correctly

Job done!

Fitting the new belt without the tool looks like this:

Turning crankshaft
  • Soak the belt really well in hot water to soften the belt
  • Fit belt to all pulleys and finish at the crank pulley (Harmonic balancer)
  • Have crank socket and ratchet to hand,
  • Offer the belt to the right hand side of the crank pulley and hold it there firmly
  • Turn the crank clockwise while your free hand guides the belt onto the crank pulley (advise long handle ratchet and removing spark plugs)
  • Continue to rotate the crankshaft until the belt is seated
  • Check the belt ribs are seated correctly

Job done, nice work MacGyver!

John Cunningham

John Cunningham is an Automotive Technician and writer on Rustyautos.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of classic car ownership, from tires to roof aerials and everything in between.

Recent Posts