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LS Radiator Guide

8/27/2021

LS engines have been showing up all over the place in the past couple decades. They make great power in stock form and respond well to bolt-ons and power-adders. As you run down the list of things you might need to swap one into your car, the radiator is one of the big expenses. Why do you need a dedicated radiator for an LS engine? This article will explain the differences and offer a few solutions.

Not only does a car like the Grand Monster Regal need a radiator to work with the late model engine, it also needs plenty of cooling capacity to cool the supercharged LS.
What’s the difference?

There are several factors at play here. First, the thermostat on most LS engines is on the water pump. Obviously, that puts it lower on the engine than we’re used to seeing on older small and big blocks. This means that these engines need a way to keep hot air pockets from forming at the top of the engine. GM’s solution was to add steam lines to vent trapped air back into the moving stream of coolant. There are lots of ways to do this, but one of the most common is to add a port to the radiator tank to attach the steam lines. Most LS swap radiators will have at least one fitting for this purpose.

This shot of an ICT Billet alternator and steering pump bracket also show the unique LS water pump. The thermostat housing is in the lower hose, and the upper is also pointed toward the passenger side.

Another unique feature of most LS engines is the orientation of the upper radiator hose. The lower hose still goes to the passenger side of the car like an earlier small or big block. But the upper hose no longer goes to the opposite (driver) side, instead it too comes out on the passenger side. The upper hose is also only 1-1/4”, making it smaller than the older engines. So, in addition to the steam line provision, an LS swap radiator will typically have an 1-1/4” upper outlet positioned on the passenger side.

What are my choices?

The popularity of LS swaps into older chassis means that there is a direct fit radiator for a wide variety of vehicles from companies like Afco, DeWitts, and Frostbite. Once you have found the radiator that fits your application, there are a few additional choices to make.

First, what finish do you want on your radiator? Depending on the manufacturer, you may have the option to select satin aluminum, polished aluminum, or black. This allows you to tailor the appearance of the radiator to match your taste and the components on the rest of your engine compartment. We chose a Black Ice coated DeWitt’s radiator with black fans to swap the 6.0 LQ9 into our Project Chevelle and it looked just like it grew there at the factory in 1972. On our ’52 Chevy truck, a brushed aluminum Afco radiator matched the stock LS3 quite nicely.

Here's the DeWitt's radiator in our Project Chevelle. It's beautiful and has done a great job cooling 500 horsepower on the street and at the track.

You will also have some choices when it comes to the fan. Once again, you can select the finish on the shroud, but often you will also be able to select the fan configuration. In other words, a single fan in the center or two smaller dual fans. Depending on the shape of the radiator, a big single fan may do a better job of covering the radiator core, but that can put the deepest part of the fan right in line with the water pump. If space is tight, sometimes dual fans can solve these fan motor to pulley clearance issues.

Is there a cheaper option?

The direct-fit radiators above can get expensive depending on the options that you select. In our experience, the convenience of just dropping a direct fit radiator into place and hooking everything up like it was a stock replacement part is more than worth it. But, if you’re on a budget, Speedway Motors has developed a convenient hack that offers a more affordable solution.

This little adapter can be a lifesaver. This version features the steam liner adapter. It's also available without.

The LS Swap Radiator Hose adapter is a low-cost option that can really help economize your LS swap. One version takes care of the upper hose diameter issue and adapts the 1-1/4” LS water neck to the 1-1/2” upper outlet on the radiator that was already in front of your old school small or big block. You might have to do some clever hose routing to make it across the radiator, but there are kits to help with that as well. This adapter is also available with a steam line attachment to eliminate the need to weld or braze on your radiator or tap into your water pump.

These adapters also open the door to using one of our budget-friendly universal double pass radiators. This puts the upper outlet on the correct side and offers a variety of widths. Also, a double pass radiator can offer better cooling than a single pass. (For more information on this style of radiator, check out this article.) The adapter and radiator are offered as a kitto make things even easier.

Pictured with a double pass radiator, this kit is a great way to get great cooling for your LS swapped car at a low price.
What about the radiator in my late model?

LS engines respond well to mods and the stock guts will handle ridiculous power. So, if you’ve upped the ante on your late model Corvette, F-body, or Cadillac, that stock radiator that was designed to handle 400 horsepower might not be up to the job of cooling 800-1000 horsepower, especially if it’s being driven hard. We’ve seen several late models come in from laps on the road course with dangerously high coolant temps. Fortunately, Speedway Motors has these applications covered as well. Afco and DeWitt’s both have a variety of direct-fit radiators for these late model applications.

We've seen Afco's 5th-gen Camaro make hard laps at the road course all day long, and the upgraded radiator kept it cool the whole time.
What else do I need to know?

This is just an overview of the many options you have to cool the late model GM LS in your car. The aftermarket has embraced every aspect of these engines and the cooling system is no exception. There are options to suit most applications and most budgets. It should be noted that there is a huge variety of engines in the late model Gen III, IV and V family. There are exceptions to every rule, and this is especially true when you start looking at some of the more exotic supercharged engines. Be sure to check the specs of the engine that you plan to run and make sure that the radiator and fan setup that you’ve picked is going to work.

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