Will additives solve my overheating problems?

December 1, 2010 | By Richard Prince


I have read and re-read all the articles in Auto Restorer about parade-proofing your car. I have had the cooling system pressure checked for leaks in my 1964 Ford with a 390 cid engine and there are none. I had the system flushed, drained and refilled and it still runs at an operating temperature of 210-230 degrees in traffic. It does cool down to about 200 degrees with open road driving.

So what are your thoughts on additives such as Kwik Kool or Hy-Per Lube super coolant? Will they do any harm?

I went through the Woodward Dream Cruise in suburban Detroit and it was very stressful in traffic—I had some anxious moments with a constant eye on the temperature gauge. Not a lot of fun!


Some coolant additives do help control engine temperature but none will compensate for a problem or combination of problems that cause your engine to run 20 or 30 degrees too hot.

Were the cylinders bored? In general, the 390 cid Ford block is a stout casting, with good cylinder wall thickness, but the odd block did have some core shifting during the casting process, causing areas of the cylinder walls to be unusually thin. If your block was bored more than .060inches it may tend to run hot, especially if the cylinder walls were a bit weak to begin with.

The head gaskets for 390 engines can install in two different orientations but only one is correct. If the gaskets are installed correctly, both cooling slots will be toward the rear of the engine. If the installation of one or both gaskets is wrong and the cooling slots are toward the front of the engine a hot-running condition will result.

Radiator capacity and efficiency are, of course, crucial to controlling engine temperature. Is the radiator in your car large enough? Is it flowing enough coolant or is the flow obstructed by clogged tubes, corrosion or something else?

Is the water pump performing as it should? Sometimes the water pump isn’t leaking and has no other apparent signs of trouble but still isn’t moving enough water because the pump’s impeller is corroded or slipping.

Even if the radiator and water pump are up to snuff they aren’t as effective as they should be if there’s insufficient air flow through the radiator. Is your fan sufficiently sized for the engine and car? If the fan has a thermostatic clutch, is the clutch working properly? Are there large gaps around the radiator that permit air to flow around it rather than through it? Air will normally take the path of least resistance. Use foam and rubber radiator seals to close up gaps and direct air through the radiator. Eliminate or relocate obstructions that are blocking air flow, such as a front license plate, fog lamps and the like.

Consider the installation of two small or one large electric fan to supplement air flow through the radiator when the engine is idling or when the car is moving slowly in traffic.

Two more factors that can adversely affect engine temperature are ignition timing and fuel mixture. Make sure engine timing is correct and adjust the fuel mixture so it’s not too lean.

And, of course, don’t overlook the simple things, including checking the thermostat’s rating and function, and the radiator cap’s function.