1991 GMC S15 Jimmy Coolant Leak Diagnosis Cost

If you have a problem with the coolant level dropping, but no signs of an external leak, the issue may be an internal engine leak. This type of leak may be due to a leaking intake manifold gasket, head gasket, or oil cooler. A shop will need to conduct various tests to find these types of leaks.

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

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.

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.

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.

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.

A pressure check of the cooling system should be performed to determine where a coolant leak is originating. After repairs, the system should be pressure tested again to verify that the repair is successful.

When a coolant hose is found to be leaking due to age and/or condition, you should replace all of the coolant hoses in order to prevent failure.

After the cooling system has been serviced or repaired, it's important to verify that the system is not leaking, the radiator fans are operating properly, and all air bubbles and air pockets are bled from the cooling system.