Cooling issue on highway

RustyRatRod said
That's where it runs best so that's what it wants. Much hotter and it has light spark knock, so that's where it has to run.

I feel you. I started the 340 in my Duster out with a 180° thermostat and a dumb flex fan, never had a problem keeping it below 190°. Except that the engine runs better at 200° than it does at 180°, so I ditched the flex fan for the electrics with a programmable controller and ran a bunch of different fan on/off temps. Just runs better at 200°F. Obviously that's tuning, and if I wanted to do nothing but drag race I would retune my A/F richer and all that and run it colder for more power at WOT. But on the street I rarely see WOT, so, I'd rather it be happy where I actually drive it.

George Jets said
Thoughts you say?

Select the desired temperature thermostat that you want your engine to run at.

Lose the shroud and electric fan. Install this 18" silent run fan without a shroud, and let the air flow through the radiator at highway speeds.

View attachment 1715952481

This setup is working on a 440 that had electric fan and shroud, and was overheating.

Running at operating temp now, now that the restricting shroud is gone.

1st test was with a 15" silent run fan we had on hand, overheating issue went away.

View attachment 1715952490

Ordered In and installed the above 18" Silent Run fan for even more cooling.

All is good now. Took it out on the highway for a workout. Yes all is good, working like it should. Stays running cool at lower rpm also.

Funny, I got rid of a POS flex fan like that on my 340. Bottom line is, if the electric fans weren't working for you they were the wrong fans. Plenty of fancy electric fans out there that don't move enough air, and there are plenty of dumb ways to trigger fans. Build a bad system, get bad results.

SlantedDart said
Maybe not zero air flow but I took the fan off to cut all the pass throughs and at some point on the freeway the fan distorted enough to scuff and melt the plastic on the fan.. it’s not letting air through it’s flexing the fan itself to let air through.

Something is wrong with your fan or your shroud. That kind of interference shouldn't be happening. That's why I'm not a fan of aftermarket fans on aftermarket shrouds, nobody designed all that to work together they just put a couple of aftermarked fans and bolted them to a baking sheet. That's not a proper shroud.