A high-performance LS engine generates much more heat than a Chevy Gen I small-block engine or a Pontiac V-8 that originally came in many of the F-Body cars, so you need a cooling system that effectively and efficiently dissipates and manages the heat. Therefore, you need the correct components, adequate capacity, and proper calibration for the high-performance engine you have installed in your F-Body. A proper cooling system helps produce horsepower and protects your sizable investment in your LS engine. Don’t cut corners; invest in an aftermarket aluminum radiator, water pump, and related equipment that’s well suited to your engine.
This Tech Tip is From the Full Book, SWAP LS ENGINES INTO CAMAROS & FIREBIRDS: 1967-1981. For a comprehensive guide on this entire subject you can visit this link:
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Interestingly, the coolant system on the LS engine lineup is not entirely different from a Gen I Chevy small-block that was installed in most of these first- and secondgeneration F-Bodies. The LS has two major ports: One comes into the engine while the other moves hot coolant out of the engine and into the radiator. Thankfully General Motors did away with the reverse cooling LT engine that seemed more of an experiment than a wellthought-out system.
Early F-Body cars run an openbottle cooling system. However, a closed pressurized cooling system with a closed overflow bottle provides higher pressure and much better cooling than a standard open system. In addition, the extra capacity of the bottle in a closed system offers more cooling. While you can use the stock system with an open overflow bottle, it doesn’t provide nearly the same cooling capacity as the modern closed system.
If you’re scrounging the junkyard, you can pluck this system from many late-model GM cars, including the Cadillac CTS-V.
When installing a closed pressurized system, the lower line should be integrated into the return heater hose. For an LS engine this is the most forward 3/4-inch nipple on the water pump housing. The vent hose from the cylinder head should be hooked to the small upper nipple on the bottle.
Although you may be tempted to use the original radiator from your F-Body with your new LS engine, this is not the right move and does not meet your high-performance goals.
While it could work, it won’t provide enough cooling capacity, particularly if you’re using your F-Body in competition. Therefore, I don’t know of anyone who has tried reusing an original radiator from the 1960s or 1970s. It’s simply not worth using an old-style radiator and risk damaging your engine. The cooling efficiency of the old-style radiators just isn’t what they are today with aluminum radiators being the norm. I highly recommend upgrading your radiator as cheap insurance to protect against heat in your engine. Newer radiators are vastly more efficient, lighter, and use more reliable components such as electric fans and have larger cooling capacity.
While you can use a small-block radiator on an LS swap, there is one major difference. The upper radiator hose needs to be routed to the driver’s side, which requires a custom application of the hose. The standard small-block radiator works exactly the same way as the LS specific radiators do, the difference is, you guessed it, the placement of the upper radiator hose.
Keeping in mind that the upper radiator hose is the “hot” side, pushing the hot engine coolant from the engine to the radiator to be cooled, the same approach must be taken regardless of which radiator you choose.
I’ve seen it done on a few cars that wanted to retain the stock smallblock appearance and not give away the deadly secret underneath. This option might be for you, but remember it takes a bit of work to make it work properly and not look like a hack job.
A myriad of aluminum cross-flow radiators are available for LS swaps into first- and second-generation F-Body chassis. The stock LS radiators have both inlet and outlet passages on the passenger’s side of the engine. While you can route hoses to the driver’s side of the engine, it’s difficult to package all the components when running non-stock hose routes. Thankfully, several companies, such as AutoRad, Flex-a-lite, AFCO, and Be Cool, offer high-capacity aluminum radiators for early F-Body swaps.
The stock LS radiator out of a fourth-generation F-Body car installs because the first-generation’s direct mounting to the core support, but it is different than the fourth-generation F-Body setup. You have to be a bit creative when mounting the radiator If you plan on running an LSspecific cross-flow radiator (and why wouldn’t you?), Goodyear makes a number of upper and lower radiator hoses that are compatible with an LS radiator, but you’re going to have to cut and fit to install them. Those part numbers are: Goodyear MH585 for the upper radiator hose and MH1235 for the lower hose. These part numbers may have been different in previous years and are not direct-fit hoses. In addition, they may be somewhat difficult to install and may take some muscle and trimming to get them in place.
While you are at the parts store rummaging through the radiator hoses for the right one, it is helpful to know that the inside diameter (ID) of the hose you’re looking for is 11 ⁄2 inches. This is for both upper and lower sizes. You might have to cut and adjust a bit on each hose to make it fit just right but if done correctly, it looks factory.
This radiator and fan combo boasts a 40-percent surface area gain over a stock radiator and a 20- percent surface area gain for even the best radiators on the market, which is impressive. I want the capability of blasting the A/C while hitting the corners hard at the track. A radiator that can keep it all under control is a big bonus to us. In addition, if I choose to upgrade to even more power in the future, this unit is up to the task and one less thing for me to worry about.
To install this radiator, the core support needs to be replaced. If yours looked as butchered as mine did, replacing it is probably a wise thing to do. Another reason I went this route is that the stock LS radiators typically have a sandwiched design; the two side-headers are made of plastic and are joined to aluminum cores. This is typically the weak spot in a modern radiator and after repeated heating and cooling cycles those joints wear down and eventually leak and need replacing.
With all the options available from AutoRad, I opted for the dual fan setup and the A/C condenser already mocked up into place. AutoRad throws in all the hardware you need so this really was a no-brainer.
Radiator Hose Location
On an LS engine, both radiator hoses route from the passenger’s side of the engine. The accessories can interfere with connecting the upper radiator for certain engines and setups for folks who want to run a stock first- or second-generation F-Body radiator or in applications where a turbo or supercharger has been added. Dropping in a dual-pass crossflow radiator resolves this problem by connecting both hoses on the passenger’s side of the engine.
An additional benefit to dualpass radiators is that they keep the coolant in the radiator longer. This allows the fan to remove more heat, and it increases the ability of the radiator to cool more efficiently. Every LS engine is equipped with a 195-degree thermostat. The major difference is that the outlet for the thermostat is not in its typical position directly on top of the intake as with the small-block. The engine must retain the thermostat because it’s a direct flow-through design, so you don’t want to remove it and damage the engine.
The LS engine doesn’t run its coolant through the intake manifold like previous Chevrolet engines did so there are some subtle differences in operation. Many swappers simply drill and tap the water pump and direct the flow straight into the water pump and back into cooling system. This works well and I have seen no problems from many different installs.
Another way to do it is to put an inline adapter from the upper radiator hose or possibly the heater hose. Either way works equally well. The real question becomes, “How much work am I willing to put in?”
A number of radiators have a steam vent bung that comes already attached to the radiator if you choose to use it; otherwise put a plug in it. This is by far the easiest conversion method, but also the least cleanlooking way to install it.
Coolant Steam Line
Another unique feature of the LS cooling system and the LS system itself is that it uses a coolant steam line. The coolant steam line is designed to vent excess air pockets from the coolant system. Air is the enemy of any proper cooling system and this system does a nice job of removing unwanted air pockets without a lot of mess. When performing a swap, you need to route and connect the tube to the upper radiator hose. This line must be hooked up or the engine could overheat.
The heater hose outlets are pretty consistent from car to car. Even the new-style C6 Corvette and the firstgen F-Body share the same heater hose size and routing plan. The LS engine locates the heater hose outlets directly behind the thermostat housing.
When looking direct at the two plugs from the passenger’s side, the rear-most port accepts a 5/8-inch heater hose and has a matching port on the heater core, this is the “in” port as hot coolant passes from the engine to the heater core. The forward-most facing port is a 3/4- inch heater hose and is the “out,” or return, side of the system. The heater core returns the cooled coolant from the heater core back into the engine.
Coolant Temperature Sensor
For some reason my PCM and gauge cluster did not like to play well together so I had come up with another solution to gauge the coolant temperature rather than the typical places. I found a coolant adapter from Auto Meter that taps into the feed line of the heater hose and uses a 1/8 NPT fitting for the coolant temperature sensor.
Remember to ground this piece or your gauge reads zero.
Electric fans come in numerous shapes and sizes. The stock Corvette and F-Body LS engine typically comes with two fans: the main lowspeed fan and one that comes on at high speed when the engine requires the extra cooling. You might want the dual-fan setup if you’re on a budget because it’s a proven system that works well. The dual fan setup can be had from junkyards fairly cheaply.
If your wiring harness doesn’t have any relays, you have to add a couple to precisely match the situation. Relays are a great way to power something off the battery without causing any serious drain and provides safety by allowing power to be turned on only when truly needed. If you choose to use a Gen IV style ECM, you have some extra wiring to complete the pulse-width modulation system. This is the same technology used in the fuel pump, essentially only going as fast as it needs to on short electrical pulses. Since this is the aberrant situation rather than the norm, I stick with the on-off style of fans.
A lot of aftermarket kits are available today. AFCO, BECOOL, and Ron Davis are just a few names in the market now. I’m sure others complete the job adequately. All of them have a variety of setups available that include bare radiators all the way up to full kits with fans, shrouds, and wiring harnesses. It’s really up to you how far you want to go with it. If you’re planning on running some big power, you might want to look toward Ron Davis or AutoRad for your cooling needs.
The fans I had on the AutoRad system use a dual 18-amp fan system. Because my Mast ECM is only programmed to work with one fan, I simply hooked up the fan wires to both fans at once. The Mast ECM is designed with a 40-amp breaker, so I had plenty of power to spare.
The LS PCV (positive crankcase ventilation) system is a little different than the standard system that is on a typical small-block. The system on the LS engine has three ports that need to be routed correctly. The LS engine, like most other engines, makes positive pressure when in operation. These pressures need to be dealt with or the engine starts leaking profusely through the weakest part of the engine, typically the gaskets. The PCV system allows the engine to expel those gases (known as “blowby”) through three ports: one on each valve cover, and one on the front port coming off the intake valley. Do not block these ports or modify them as they provide crucial venting for your shiny new engine. The last thing you want is a sick, weeping, and puking pile of aluminum.
If you choose to order a crate engine from Chevrolet Performance or a GM dealership, be aware that their instructions are slightly different but that both work.
The strict Chevrolet Performance instructions say that you should connect the two foul side ports to the intake manifold and be exposed to vacuum at idle. These two ports are the valley port and the driver-side valve cover port. The passenger-side port should be connected to a clean air source such as the air cleaner. If you chose to use a MAF sensor on your car, the passenger-side port should be mounted between the MAF and the throttle body, typically on the intake tube. If the port is connected before the MAF, it confuses the sensor and possibly throws an erroneous code.
I set up this system as simply as you would want to. I routed both valve cover ports to a T-fitting with 3/8-inch vacuum line and then a single line to a small and unobtrusive catch can to catch any excess blowby. The can is topped with an air cleaner so that any return air or oil isn’t contaminated. The valley port is connected to a vacuum source, this can be virtually any vacuum source, such as a brake booster, but I chose the shortest and easiest route, which is directly to the intake pipe right before the throttle body.
Written by Eric McClellan and Posted with Permission of CarTechBooks