Choosing and Using Engine Oil Coolers

Choosing the right engine oil cooler for a given application can seem like an overwhelming task. Setrab Oil Coolers come in so many shapes and sizes, it's hard to know where to begin. Even their application chart gives you multiple different choices for most engines. A few general tips will help you to narrow down the available options and choose the best one for your specific installation.

Before We Begin

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For the purposes of this article, we will focus on plate-type oil-to-air coolers, such as the Setrab Pro Line. Finned-tube coolers and oil-to-water heat exchangers operate just a little differently. Since we don't offer either of those types, we're going to take the liberty of ignoring them.

Also, in order to avoid apples-to-oranges comparisons, please remember that all assertions imply "all other variables being equal." AGREED, you can change another part of the equation to get the answer you want. Like a track test or dyno run, changing just one factor at a time makes the effect of that change much clearer.

Start with the Chart

Setrab USA has gone to the trouble of providing us with a very handy oil cooler application chart (PDF format) that gives us a starting point without having to do math. The chart covers engine oil coolers, transmission coolers, and even power steering and valve spring coolers. Note that the chart is arranged by part number, not by application. Browse the chart a bit and you'll see that most applications are listed under more than one cooler size.

Oil Flow Restriction and Cooling Performance: Rules of Thumb

Here are some broad, oversimplified, very general principles to keep in mind when choosing a cooler. Remember that all of these imply "all other variables being equal."

• Oil coolers introduce a flow restriction. Our goal is to minimize this restriction.
• There is a direct relationship between plate length and restriction.
  Longer plates (rows) = more restriction.
  Shorter plates (rows) = less restriction.
• There is a direct relationship between plate length and cooling effect.
  Longer plates (rows) = more cooling.
  Shorter plates (rows) = less cooling.
• There is an inverse relationship between the number of plates and restriction.
  More plates (rows) = less restriction.
  Fewer plates (rows) = more restriction.
• There is a direct relationship between the number of plates and cooling effect.
  More plates (rows) = more cooling.
  Fewer plates (rows) = less cooling.
• Two coolers with similar cooling area will have similar cooling performance.

In the list above, the only apparent conflict we have to wrestle with is in plate length. Longer plates cool better (good), but at the expense of flow (bad). Fortunately, the last point in the list above suggests a good workaround: We can choose a shorter cooler to regain some of the lost flow, and simply add more rows to regain some of the lost cooling. Even better, adding more rows simultaneously improves flow even further.

Let's take an example from the Setrab application chart and do just a little math. Say we have a high-performance engine putting out about 325 HP. The chart suggests at least three possibilities: Series 9 with 20 rows, Series 6 with 25 rows, or Series 1 with 50 rows. All three of these coolers have an effective cooling area right around 75 square inches, so their cooling performance is similar.

But the Series 9 will have the most flow restriction (longest rows x fewest rows), and the Series 1 will have the least restriction (shortest rows x most rows). As it turns out, the 25-row Series 6 will have about half the pressure drop of the 20-row Series 9, and the 50-row Series 1 will have roughly 1/10th the pressure drop of the Series 9!

Using real numbers, with a 10 GPM flow rate as an example (not uncommon for an engine running - RPM), the 20-row Series 9 will introduce a 5 psi pressure drop from inlet to outlet. (Note that a single 90 degree fitting in your oil line could cause more restriction than that.) The 25-row Series 6 will cause a 2.6 psi drop. The Series 1 will show less than a 1 psi pressure drop. The flow restriction from the Series 1 option may not even register on your oil pressure gauge.

Installation Factors

There are just two general rules when it comes to mounting the cooler. (Remember, "all other variables being equal.")

• Oil coolers require airflow to take heat away. More airflow is better.
• Cooling depends on the difference in temperature between the air and the oil. Cooler air cools better than warmer air.

The airflow equation is a little complicated. As airflow velocity increases, the additional benefit decreases (the graph begins to flatten around 40 mph). The important takeaway is that your oil cooler needs to be exposed to airflow. The largest oil cooler will be ineffective if it's sealed in the trunk or mounted flat up against the firewall. Air must be able to get into the cooler, and it must be able to get out of the cooler. This is what carries away the heat.

In many cars, this suggests mounting the cooler near the radiator. After all, Detroit / Stuttgart / Tokyo spent a lot of time and effort to locate the water radiator where it would get the best airflow. It seems like a no-brainer to follow their lead. But that leads to the second point above.

Air temperature has a direct effect on oil cooler efficiency. Hot air does not cool as well as cool air. This is why we turn on the AC when we're hot, and not the heater. Mounting the oil cooler behind the radiator can reduce the efficiency of the cooler by as much as half. A better solution would be to mount the cooler in front of the radiator. The trade-off is that the efficiency of the radiator will be affected by the air coming through the cooler, but the effect should be much smaller because the cooler is typically smaller than the radiator. An even better option would be to mount the cooler next to the radiator (assuming there is room) or below the radiator (if it can be protected from damage).

The air temperature difference also means that if we run two oil coolers, they should be plumbed in parallel, rather than in series. If you run two coolers in series, the oil in the second cooler would be cooler (closer to the air temperature) than the oil in the first cooler, making it much less efficient. Another bonus to plumbing in parallel is that it has the same effect as adding more rows to the cooler: Less flow restriction for an even happier oil system.

Much more information about mounting oil coolers for maximum air flow with minimum drag can be found in Chapter Nine of Tune To Win by Carroll Smith.

Final Tips

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An oil cooler is a fairly simple component, which means that it rarely fails. However, when doing any major engine work, it should be replaced. There are many reasons why a diesel engine can fail. And when it does, the oil cooler should be swapped out as well.

Used oil coolers are known for holding debris, making them a prime source of catastrophic engine failure. If you went through the trouble of doing a full rebuild or engine swap, a simple oil cooler replacement is the best insurance one can buy. Here are some warning signs that your diesel engine may need to be rebuilt.

As you might have guessed, the main job of an oil cooler is to bring down the oil temperature in your diesel engine. It does this by allowing hot oil to run through the main rifle on the cooler. There are several benefits to having lower engine oil temps, including better lubricity, decreased wear on key engine components, and of course, prolonged engine life.

Unfortunately, most oil coolers do not have a bypass, meaning they cannot be flushed or properly cleaned out. If debris enters the engine and is suspected to have made its way into the cooler, it is recommended that the entire unit be replaced to avoid any further damage.

Heavy-duty diesel engines found on commercial and farm equipment are commonly equipped with oil coolers in an attempt to keep engine operating temperatures in check during extremely high loads. Keeping the oil temperature within the manufacturer’s specified recommendations will not only increase power but will also help ensure a long life.

Oil Cooler Types

Oil coolers are not all the same. They come in various shapes and sizes depending on the manufacturer and its intended application. Here are the most common oil cooler types:

Filter Mounted

A filter-mounted oil cooler is attached to the oil filter itself. The hot oil is circulated through the engine and enters the cooler before passing through to the filter. Then, the cool oil is pumped back into the engine ready to start the cycle all over again.

In-Tank Filter

This method of cooling the oil is perfect for applications where space is at a premium as it uses the real estate already taken up by the engine’s radiator. It can use both cool air flowing over the fins as well as the coolant to quickly and efficiently lower the engine oil temperature.

Remote Mounted

Accurately named, a remotely mounted oil cooler can usually be mounted to the engine block or transmission. Additionally, remote-mounted oil coolers can be air or water-cooled, depending on the application.

Air Cooled

Air-cooled oil coolers are commonly put in front of radiators or somewhere that allows plenty of fresh air to cycle over them. Similar to a normal radiator, the cool oil passes over the tubes as the air flows over the vanes. The heat is then drawn out of the oil, which effectively cools it.

Water Cooled

Alternatively, water-cooled oil coolers rely on the engine’s coolant system to lower the oil temperature. One of the main benefits is that it allows the cooler to be mounted anywhere there is available space. The physical size of the cooler can also be reduced as there is no need for additional fins that draw out heat. It just needs to be plumbed to the vehicle’s cooling system.

Engine Mounted

This type of cooler can be found on most modern engines including diesel, gasoline, and even flex-fuel. They are mounted directly to the engine block and work by using the engine’s existing coolant system. Engine mounted oil coolers are ideal for high-speed applications that need additional cooling for increased workloads. If space allows, the cooler can take advantage of the engine block’s heat exchanger, eliminating the need for extra plumbing.

Oil Coolers Are Commonly Found On 

• Tractor-trailers and other vehicles designed for long haul freight
• Vehicles specifically designed for off-roading
• Certain RV’s
• Specific race and sports cars/trucks

Common Problems With Hot Engine Oil

Your diesel engine’s oil has many jobs. Most notably, it is intended to lubricate, cool, and clean the engine. However, as it heats up, the lubrication properties tend to break down. This is where an oil cooler comes in.

Ideally, engine oil temperatures should remain between 180 and 200-degrees. But the optimal temperature cannot always be maintained, especially for engines with a high amount of work. This is why certain manufacturers fit oil coolers to diesel engines. Some of our customers look to get auxiliary oil coolers installed to cope with increased workloads.

Why Do You Need To Replace The Oil Cooler?

As previously mentioned, there are several reasons as to why someone would need to replace the oil cooler. Replacing the oil cooler could help restore list power in your diesel engine. Additionally, it can prevent future issues from occurring as most oil coolers cannot be cleaned.

Final Words

Highway & Heavy Parts has a variety of oil coolers, EGR coolers, water pumps, thermostats, and anything else you might need to keep your engine’s temperatures in check. Our wide selection of OEM and aftermarket parts is sure to get you back on the road in no time at the best possible price.

Do you have any questions about oil coolers or other diesel engine parts in general? Our ASE-Certified staff is standing by and ready to answer your questions. Gives us a call at 844-304- or request a quote online today!

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