76Vett

At highway speeds, my electric fans never shut off. I have a Dewitts Alum Radiator w/ dual fans. Installed the air dam today, took the car out for a 25 miles run and again, they never shut off. Car doesn't over heat - I can go for a run, shut it off and immediately restart it. Motor is new, less then 250 miles. I did receive the "foam" seal kit and will put it on tomorrow, and hope that helps. At idle and under 15 mph or so, they almost never come on. What else can I do? How big of a PITA is that seal kit to put on now that everything is already put together?

hugie82

You have to keep backing the thermostat off until the temp starts going past the tremostat setting. Say if its a 190* , back it off until it starts touching 200* than turn it up a notch.
Also, where is your thermostat reading from? Radiator fins, hose or block?

76Vett

I have the "stock" temp sending unit to my gauge and when it get just past 200, the fans come on. Dewitts Radiator has a temp sending unit in the radiator and wired thru a relay to operate the fans - per Dewitts, fans will come on at 195 and off at 180. I'm not sure I understand your comment to "keep backing off the thermostat . . . ."

John A F

I would say check your wiring. I have the exact set up and the fans never come on at highway speeds. They will come on with periods of extended idling or stuck in slow moving traffic. They are very efficient and will cool down the engine temp within three to four minutes. I am using the stock thermal switch located in the radiator. (On 195, off 175). You will have to loosen up your radiator to install the seals. They should have been installed before the radiator is mounted. Location of the seals is shown in the AIM.

MrJlr

You need the foam strips installed.
The highway speed air is going around the radiator instead of through it, thus the higher rpm and engine heat needs the fans to cool the radiator.

chevymans 77

Curious how you can tell they don't shut off at hwy speeds?

Neal

76Vett

My AMP Gauge moves to the right when the fans come on.

MrJlr

Lol......that'll do it

I went to a 140 amp alternator when I did mine.
Doesn't even twitch.

donyue

Hi 76Vett,

Keep advising how your "foam" seal kit install progresses. I had recently installed a Dewitts aluminimum with Dual Spal fans and I notice that the fans come on quite often.

I would like to know if the foam seal install is worth the trouble to install.

Maybe someone from DeWitts will review this thread and offer their opinion?

doorgunner

It almost sounds as though the thermal switch is functioning "backwards" ..... it is closing/supplying voltage to the fans when the coolant is "cool" at highway speeds......

But.....like another member said--The fans could pulling most of the air thru the "gaps" between the fan shroud and the radiator.

76Vett

Still haven't put the seal kit in, been raining here the last few days. I'm sure with all the postings I have read that this will fix it. I'll get it in soon and post results.

qwank

if the temp in the radiator where the sensor is is always at the turn on and run temp, they will never shut off. so if you arent seeing 180* cruising on the highway, why would you think they would shut off?

76Vett

Just to clear up some things, as my original posting may have been misunderstood. I can let the car idle in the driveway and the fans operate as they should. When the temp gauge gets to around 210, the fans come on and go off when it shows less the 200. The gauge isn't as accurate as it should be and I have changed the sending unit a few times. The one I have now is the closest. At hwy speeds the temp come up, fans come on, but never go off. The seal kit should help here as many other have posted that their electric fans never come on a hwy speeds. Anyway - weather permitting, I hope to add the foam seals, seal up a few other areas and get the air directed thru the radiator instead of around it.

Phil Zell

I too run the DeWitts and do not have the foam seals. Car has never been hot.

roger3

I have 76 with BBC and Dewitts rad with dual spal fans. It does the same thing as yours (works fine at idle and low speeds but never turns off on hwy as temp slowly creeps up to about 220f). I have all new seals In place.

I am following your thread to see what you come up with.

Chevyman 77 got a handle on his by adding an external oil cooler.

I want to try a couple more things before I go to that. I am going to add a valance seal like the earlier c3's had to try and seal up all places air can escape. I'm also going to remove the ac condensor.

Roger

76Vett

Made some progress today. Temps are only in the mid 60's so not the best to check progress. So I ran the car at 65 MPH for 5 miles down the hwy - Fans came on almost immediately and never went off during the run. Came back and installed the Radiator/core support foam seals and a hood to core support seal. Made the same run and the fans never came on. Car runs a lot cooler by the temp gauge. Still have a few little things to seal up but I would never have believed that those foam seals would have made that much difference - no doubt, they must be installed - even with a Dewitts Radiator.

MrJlr

For sure...

Those are there for a VERY good reason.
GM would never have put them there if they weren't necessary.