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Estimates last updated October 16, 2025

1991 Mercedes-Benz 420SEL Coolant Leak Diagnosis Cost

The average cost for a 1991 Mercedes-Benz 420SEL Coolant Leak Diagnosis is between $61 and $90.

Labor costs are estimated between $61 and $90.
This range does not include taxes and fees, and does not factor in your unique location. Related repairs may also be needed.

For a more accurate estimate based on your location, use our Fair Price Estimator below.

Coolant Leak Diagnosis

What is a coolant leak?

The engine cooling system is made up of a set of components that circulate coolant through the engine to keep it from overheating. If one of the components fails, it can result in coolant leaking out.

What are the symptoms of a coolant leak?

Common symptoms of a coolant leak include:

The engine runs hotter than normal, or overheats

You see a puddle of coolant under the car, or on parts under the hood

You notice the somewhat sweet smell of coolant in or around the car

The check engine light or temperature warning light comes on

Can I drive with a coolant leak?

If you notice a coolant leak, or if your car is overheating, don't drive it — doing so can cause serious (and expensive) damage to the engine.

How often do coolant leaks happen?

Engine coolant leaks are typical for all vehicles, old and new, without regard to mileage. Driving conditions, driving style, age of the car, and lack of maintenance can all make coolant leaks more likely. Maintaining the cooling system will dramatically reduce the number of leaks the vehicle will have over time.

How are coolant leaks diagnosed?

The first thing mechanics check when dealing with coolant leaks is the radiator cap. This part keeps the cooling system properly pressurized, so when it fails, problems ensue. After the radiator cap, the vehicle will be inspected for obvious leaks, damage to cooling system components, and contamination in the coolant reservoir. If contamination from combustion exists in the cooling system, the engine cylinder block, cylinder head and head gasket are suspected. If no leak is noticed, and there's no obvious sign of damage, the technician will apply a pressure tester and UV dye to the cooling system, causing the leak to become visible with a UV flashlight.

Mercedes-Benz Coolant Leak Diagnosis Cost Estimates

The average cost for a Coolant Leak Diagnosis is between $61 and $90 but can vary from car to car.

Mercedes-Benz 420SEL Coolant Leak Diagnosis Cost by Year

The average cost for a Mercedes-Benz 420SEL Coolant Leak Diagnosis is between $61 and $90 but can vary from car to car.

1991 Mercedes-Benz 420SEL

$61-$90

1990 Mercedes-Benz 420SEL

$61-$90

Coolant Leak Diagnosis

Jump to:Commonly associated repairs Cost estimates by vehicle Cost estimates by year

What is a coolant leak?

What are the symptoms of a coolant leak?

Common symptoms of a coolant leak include:

The engine runs hotter than normal, or overheats

You see a puddle of coolant under the car, or on parts under the hood

You notice the somewhat sweet smell of coolant in or around the car

The check engine light or temperature warning light comes on

Can I drive with a coolant leak?

If you notice a coolant leak, or if your car is overheating, don't drive it — doing so can cause serious (and expensive) damage to the engine.

How often do coolant leaks happen?

How are coolant leaks diagnosed?

How is a coolant leak fixed?

Repairing a coolant leak typically requires draining the engine coolant from the entire system, removing the faulty part, and either cleaning or replacing that component before reinstallation. Internal leaks tend to mean expensive repairs — a new head gasket or a new or refurbished engine being the most likely. Most often, though, repairing a leak involves a simple hose replacement and coolant flush.

RepairPal recommendations for coolant systems

On older vehicles, it's often recommended to flush the cooling system every two years or 30,000 miles. Many newer vehicles have extended-life coolant that can last up to 100,000 miles. It's always recommended to follow the service intervals in the owner's manual. Following the required services listed, whether it's a coolant change or coolant flush, will help ensure the longevity of the cooling system, as well as the rest of the vehicle. Outside of routine maintenance, coolant may need to be drained and replaced when repairing a cooling system leak. In that case, a full coolant flush should be performed if excessive corrosion is present, or if the factory scheduled service interval has already been passed.

Can I fix a coolant leak myself?

The average DIYer can maintain the engine cooling system without much trouble, but diagnosing the point or cause of a leak can be tricky. For instance, replacing a leaky hose is extremely low in difficulty. In contrast, replacing a water pump requires the removal of timing components and is not recommended for the DIYer. Don't use stop-leak products, as they can eventually cause clogs or contamination in the cooling system.