How to Choose the Best Radiator for LS Swaps on a Budget

There are several things about LS engines and LS conversion radiators that are different. 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.

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.

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.

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.

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 our Toolbox article on multi-pass radiators. The adapter and radiator are offered as a kit to make things even easier.

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.