Some Like It Hot: How Engine Temperatures Have Changed

By Jefferson Bryant

There is a big difference between an old-school small-block Chevrolet and a new Gen-V LT1, and it has nothing to do with fuel injection, engine design, or even horsepower. One of the biggest differences that may disturb you is the operating temperature. If you have swapped an LS, LT, Ford Coyote, or Gen III HEMI into your classic car, you may freak out when you see the temp gauge going well passed 200°F, upwards of 220. Relax, this is just fine.

In the olden days, the target run temp for most engines was around 190°F. The main reason for this is the longevity of the engine. Most engines were built with cast iron, which expands more when subjected to the same temperature as aluminum (as much as 2-3 times), which is what most modern engines are made from. As the engine heats up, everything gets bigger, tightening some gaps, while making others bigger. This creates havoc inside an engine, so the target of 190°F kept things in the safe zone.

The biggest factor, however, is efficiency. With modern EPA restrictions, it is critical for engines to be as efficient as possible, which helps both the environment and your wallet. A hotter engine burns less fuel and makes better use of the fuel it burns. Additionally, a hotter combustion chamber burns off more of the nasty oxides that pollute our air, furthering the environmental benefits.

A modern engine, such as Gen V LT-series engine runs much hotter than an old 302 or SBC 350, about 30-degrees hotter. If you are using ECM-controlled fan, you might get concerned when the fans don’t kick on as the temp gauge approaches 200°F. The cooling fans on a Gen V LT don’t even turn on until the engine has reached 210°F, a number that would have most gearheads sweating, as we typically set electric fans to come on around 175-180°F. This is where most swappers realize that late model engines run much hotter.

In a stock late-model vehicle, this is not biggie, the components are designed for this level of heat, and are performance matched. In a swap, however, you may quickly realize that your cooling system is not ready for the higher temps. The biggest issue would be the radiator cap, which we have discussed in a previous article. A modern engine is designed to use a closed cooling system, so that it can purge coolant when necessary, and pull it back in when it is needed. An open cooling system will spit out a lot of coolant with a 7-lb radiator cap, and next thing you know, you are low on coolant. Because the boiling point of water is raised under pressure, an open system with a 7-lb cap can’t hold up to the pressures of 220°F like a 15-lb cap can, which can raise your engine temps even higher, and you end up in the danger zone above 230°F.

The point is that when you do a late-model engine swap into your classic car, you need to be prepared for some key differences that you might not expect. Your cooling system should be optimized for the engine you are running, factoring in the higher temperatures at which modern engines run. Your only change could be adding a closed-loop expansion tank and 15-lb cap, or you may need to revamp the entire system to reduce the stack-up in front of the radiator for maximum efficiency. Before you fire up your engine swap, give U.S. Radiator a call at 800-421-5975 to discuss your vehicle’s needs and they will help create a plan that will keep your temp in the sweet spot for maximum efficiency and power.