Bad Oil Cooler Symptoms

Reviewed by

Richard McCuistian, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Written by CarParts.com Research Team - Updated on May 30th, 2024

Reading Time: 5 minutes
Summary
  • The oil cooler is responsible for keeping the oil within its ideal operating temperature, which is around 230 to 260 degrees Fahrenheit.
  • There are oil-to-water oil coolers and oil-to-air oil coolers. Oil-to-water oil coolers transfer heat to coolant, which is dissipating through the radiator. Oil-to-air oil coolers have dedicated heat exchangers dedicated to oil.
  • A faulty oil cooler will leak oil, have coolant leaks, cause oil to mix with coolant, illuminate your vehicle’s warning lights, and create strange noises.

What is an oil cooler? Oil coolers function as an extra cooling device for the engine since they create a tremendous amount of heat. Vehicle engines have cooling systems that send water or coolant through coolant channels in the engine to dissipate heat. However, engine oil also needs to be cooled because it flows around the pistons, crankshaft, and valves, which can get extremely hot because of their proximity to the combustion chamber. If engine oil heats up too much, it will lose its lubricating and cooling ability. High oil temperatures also accelerate oil breakdown, causing engine oil to turn into sludge and deposits and cause a wide range of engine issues.

What Does an Oil Cooler Do?

The oil cooler is responsible for keeping the oil within its ideal operating temperature, which is around 230 to 260 degrees Fahrenheit. Oil coolers are essentially heat exchangers, which are components that function similarly to a vehicle’s radiator. These components are designed to have a lot of surface area, so that they can radiate as much heat as possible to the surrounding air or coolant, depending on the type of oil cooler. Oil-to-air oil coolers are typically located behind the vehicle’s grilles, near its radiator. This location provides the maximum amount of airflow, which is necessary for heat to dissipate effectively.

How Does an Oil Cooler Work?

There are two types of oil coolers. There are oil-to-water oil coolers and oil-to-air oil coolers.

Oil-to-Water Oil Coolers

Hot oil that comes from the engine block is fed through the oil cooler’s tubes. Engine coolant or water from the vehicle’s cooling system flows around these tubes. The oil heats up the tubes and this heat is absorbed by the surrounding coolant or water. This coolant is then directed to the vehicle’s radiator, which dissipates the heat using air.

A Dodge Durango oil-to-water oil cooler | Image Source: Richard McCuistian

Oil-to-Air Oil Coolers

These oil coolers work similarly to the vehicle’s radiator. The oil is sent to the heat exchanger, which is a set of thin tubes that have many thin metal fins connected to them. The thin tubes and metal fins allow heat to quickly dissipate through the surrounding air. These oil coolers will leak oil onto the ground but won’t leak oil into the coolant.

An oil-to-air oil cooler | Image Source: Richard McCuistian

Faulty Oil Cooler Symptoms

Oil coolers in cars wear out over time and can eventually fail. When this happens, your vehicle will show several possible symptoms such as the following:

Oil Leaks

An oil cooler adapter connects the engine’s oil lines to the oil cooler. If the oil cooler adapter or the o-ring that connects the oil cooler to the adapter is damaged, then oil can leak out of the engine and create puddles under your vehicle. The oil cooler can also leak oil.

Having an oil cooler that leaks is a serious issue because it can cause low oil levels, which will deprive your engine of oil’s lubricating and cooling properties. Eventually, low oil levels can cause your engine to overheat or even seize. If you notice oil leaking from your vehicle, we recommend that you reach out to a trusted mechanic so that they find where the leak is coming from and seal it off immediately.

Coolant Leaks

Since oil-to-water oil coolants use oil or water, a damaged oil cooler can leak coolant. When this happens, your vehicle’s coolant reserves can get low. This can cause your vehicle to overheat.

An overheating engine will cause pistons to warp, gaskets to leak, and can even crack the engine block. The engine might also make horrible knocking and grinding noises. If kept running, the engine can get severely damaged or seize.

Oil Mixing With Coolant

The oil cooler is designed to contain both oil and coolant in separate compartments. A damaged oil cooler can develop small internal cracks that can cause oil and coolant to mix.

Since pressure in the oil cooler is always higher than cooling system pressure, and the cooler is pressurized with the oil that is flowing through it, the oil tends to make its way into the coolant rather than vice versa if the oil cooler is the issue. | Image Source: Richard McCuistian
If there is coolant in the oil, this will typically be the result of a blown intake gasket. The location of the contamination is a good indicator of whether the oil cooler has failed as opposed to something like an intake gasket. Check the dipstick and under the oil filler cap for large amounts of this. Small amounts might just be a cold-running engine, so be careful when diagnosing the issue. | Image Source: Richard McCuistian

The coolant in your reservoir will turn into a thick, discolored fluid that resembles gravy if it’s mixed with oil. Similarly, your engine’s oil will also change its color and consistency.

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: The more oil there is in the coolant, the thicker and uglier it will get.

This Saturn oil cooler failed and contaminated the coolant. It took a lot of flushing and dishwashing liquid to take care of this issue. | Image Source: Richard McCuistian

Illuminated Warning Lights

Most modern vehicles come with sensors that can detect engine oil and cooling system problems. If the oil cooler fails, it can cause warning lights to illuminate on the dashboard. These can include the check engine light, the oil pressure warning light, and the engine temperature warning light. If you see any warning lights on your dashboard, you ask an experienced mechanic to inspect your car.

Strange Noises

A faulty oil cooler can also cause strange noises like knocking, ticking, or rattling. These noises could suggest severe engine damage as a result of low oil or coolant levels. You might also feel excess vibrations from your vehicle.

About The Authors
Reviewed By Richard McCuistian, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Written By CarParts.com Research Team

Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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Published by
CarParts.com Research Team and Richard McCuistian, ASE Certified Master Automobile Technician
Tags: oil-cooler