Temperature difference between upper and lower radiator outlets

[Adam G]

Just curious what an ideal temperature swing would be between the radiator inlet and outlet. My scenario is a LS1, CBR aluminum radiator with two 12” SPAL fans. Delphi computer cuts the fans in at 201 and out at 185 if I recall correctly. With the engine idling in 90° ambient air, my upper radiator fitting reads 205ish with an infrared temp gun (aluminum AN fittings upper and lower) while the lower reads about 180°. My fans run constantly once the engine reaches operating temperature in this scenario. This has lead to the occasional burned up fan relay. For reference the computer did have triggers for the fans to come on separately, but they have since both been wired together on the cooler circuit. The temp gun on the cylinder heads reads about 187~190.

 

[Goatpoker]

I’ve never quite understood why people make the On-off ranges so wide. The goal is tight temp control, not a 20-30degree range.

Trying to cool the water from 200 to 185 takes a lot of air. That’s why the fans run so hard. Might consider putting the trigger range tighter together, like 205-200.

Your original question on what is a good delta T for inlet depends a bit on the conditions. 20deg delta is really good. Is that with the fans on? Or just after they shut off? Where the water temp sensor is located has an effect as well. (Note: if you are trying to get the water temp in the cylinder head to 185 and your radiator outlet is 180… that’s only a 5 degree delta inside the head)

 

[Sandkist]

With or without a tstat?