Engine Swap Fluid & Tire Fitment Guide: Coolant, Oil, and Wheel Size Tips

Dan writes: Good morning Sajeev, I am doing a double engine swap—installing the good engine into a good car and the less reliable engine into the less reliable car. This involves a lot of fluid replacement, so I have a few questions.

Coolant Selection for Mixed Engine Materials

One engine is a small block Chevy (SBC), all iron except for the intake manifold. The other is a ZZ3 SBC with aluminum heads and intake manifold. Both have aluminum radiators. What coolant should I use? Does the iron or aluminum component determine the coolant type?

Oil Capacity Confusion After Engine Swap

How do you determine the correct oil amount when dipstick tubes are modified or the oil pan is unclear? For Gen 1 SBCs, I assumed 5 quarts and marked the dipsticks, but now I’m second-guessing my decision.

Finding Replacement Tires for Classic Cars

I have four old cars with 15-inch and 16-inch wheels. Years ago, I replaced tires that aged out despite minimal tread wear. Now, I prefer used tires, but 15- and 16-inch tires are becoming scarce. What wheel diameter is most common for passenger cars with 5×4.75-inch and 5×5-inch bolt patterns?

Sajeev’s Answers: Straight to the Point

1. Coolant Choice for SBCs with Mixed Materials

I love it—these questions are right to the point! Let’s answer in kind.

OATs for SBCs? In theory, coolant is dictated by the vehicle’s owner’s manual. For crate motors, a quick call to the manufacturer—GM Performance, in this case—is the fastest way to confirm the right coolant.

The engine material does influence coolant selection. Older 100% cast iron engines (and brass radiators) typically use traditional green coolant, formally known as Inorganic Acid Technology (IAT). Organic Acid Technology (OAT) is far superior for aluminum components. GM’s Dex-Cool is an OAT, and mixing it with non-OAT coolants is a bad idea. Hybrid Organic Acid Technology (HOAT) is mixable with other coolants, and Si-OAT is common in European engines.

Both of your SBCs can safely use OAT or HOAT to simplify your garage’s fluid inventory. You might even use it across all your vehicles, but research thoroughly before switching. If you do, flush out all IAT coolant from components like your heater core.

2. Oil Capacity: Trust the Oil Pan Specs

Oil capacity is determined by the oil pan’s specifications. Dry sump systems depend on plumbing and reservoir size. Always verify the oil pan’s capacity rather than relying on assumptions.

3. Tire Fitment for Classic Cars

For passenger cars with 5×4.75-inch and 5×5-inch bolt patterns, the most common wheel diameters today are 16 and 17 inches. While 15-inch wheels are still available, they’re becoming harder to find in used tire sizes. Consider upgrading to 16 or 17 inches if possible, as they offer more modern tire options.