Cooling System

LS engines make a lot of heat in a tight bay. Plan radiator capacity, fan strategy, and oil cooling early — especially on BK1 cars with less front clearance.

Before You Start — Clearance

• BK1: get a Corvette-spacing front accessory drive. You can get away with F-body (middle) spacing, but you want as much room as possible between the engine and the radiator fans.
• BK2: much more front-end clearance — about 1.5" more.

Radiator & Oil Cooler

Run a 3.8 upgraded radiator with a fan shroud. Jason Riddle makes them — reach out to him for one. To keep temps down you can also try a push/pull setup: most run 2 puller fans behind the radiator, and some add 1 or 2 pusher fans in front.

An oil cooler is advised to help control oil temps.

Example fan/shroud: 12" HP SPAL fans on aluminum shroud with louvers (26" x 19.5").

Radiator Hoses

Future addition.

Radiator Fans & Relays

3 OEM radiator fan wires:

I cut open the middle of the wiring harness at the firewall and pulled the thick red/green wires back toward the battery, enough to reach the new fan relays. The Kiazen relays don't need a 12V trigger lead since they're solid state, but with a traditional relay you'll need a fuse tap to a 12V key-on source for both relays. Wire in 2 relays, one per fan. The Holley gray/yellow (fan #1) and gray/red (fan #2) trigger wires go to pin 85 as triggered ground.

Using the Stock Fan Relays

In the passenger-side fuse box, the two white wires with a black stripe are power to the driver's-side fan high/low relays — apply 12V key-on power here.

Each year/model ECU connector has a different pinout. The green (high) and blue (low) wires should be your fan relay ground triggers; these go to the Holley ECU fan wires.

Stop Fans Running at Key-On

To keep Holley from kicking the fans on until after the car has started: Terminator X Tuning — Disable Key-On Fan Operation.

IAT Sensor

With the radiator blowing hot air directly at the IAT sensor I was getting wildly incorrect air temp readings. I originally put mine in the 90° coupler at the throttle body since that's where the Holley harness reached and there's no spot for it in the FAST 102mm intake manifold.

I've now moved the IAT to the back of the FAST 102, tapped for 3/8" NPT. This requires grinding down the tab that's in the way.

Steam Vent Line (Don't Skip This)

The LS thermostat sits low in the water pump housing, so air gets trapped at the top of the heads. The steam ports bleed that air off. Without them you get hot spots, which can lead to overheating and detonation.

• Connect the steam ports (two at the front on later engines, four on early ones) and run the common line to a port just below the radiator cap.
• Don't route it to the overflow port. Routing it to the water pump is debated: LSX Mag lists a tapped water pump port as an option, but Motion Raceworks says the pump just recirculates the steam.
• Many aftermarket swap radiators don't have a steam fitting. Check before you buy, or have one welded in.
• An engine that sits level (common in swaps) benefits from a four-corner steam kit.

Heater Hose

The heater core inlet is on the driver's side and the outlet is on the passenger side. 3/4" hose fits great on both. The hose below was cut on the short end to fit behind the heads — use adapters and extend it to the pump. The driver's-side port goes to the smaller rear port on the pump; the passenger-side port is the return to the front port on the pump.

Swap heater hose 90° bend + 2 clamps, 3/4" ID (19mm) 5" x 25" for LS LQ4/LQ9

Community & Parts Links

• Swapped GCs (Facebook)
• Genesis Coupe LS Swaps (Facebook)
• All-year shop manuals & wiring diagrams (Google Drive)
• Sikky LS swap kit
• LOJ Conversions
• ISR Performance mounts
• Jason Riddle / Dream Machine Z