Howdy,

While not a Corvette question per se, that’s where the problem is.

Bottom Line: The electric cooling fan turns off when the coolant temperature is high.

Detailed Sob Story: My 1978 came to me with electric cooling fans (side by side) on what I assume is an aluminum radiator. The car’s temperature gauge appears to be working properly so I am basing my observations off that.

I start the car and let it idle. At a temperature of about 190 degrees (if not lower), the fans come on. They stay on for two and a half to three and a half minutes. The temperature gauge may show a slight decrease in temperature. After the fans cut off, the temperature gauge shows an increase in temperature to just above 200 degrees. The electric fans come on again. This time, they stay on for about one and a half minutes. I do not see a noticeable temperature decrease from the gauge. After the fans cut off for the second time, the temperature needle starts a steady march to the right. The fans may or may not have a chance to come on again before I shut off the engine.

Why don’t the fans stay on?

What I have: The car came advertised with a ZZ6 crate engine. However, there have been modifications as the intake manifold doesn’t match the documents that came with the car. What do I really have? I wish I knew enough to answer.

The fan control switch is installed in the front of the manifold. From the manufacturer's site, the switch is supposed to close (turn fans on) at 180 degrees (Temperature & Pressure Switches - Electric Fan Engineering). The owner of the manufacturer told me the switch location was wrong and that this would cause the switch to read incorrectly. Though I told him of my problem, he did not indicate if the cycling of the fans was a potential result of the switch’s current location.

Could it be as simple as moving the temperature switch? If so, where would its new home be?

I’d appreciate any thoughts on fixing this.

 

Remove the entire electric cooling fan system,......reinstall factory clutch fan. And of course, the entire cooling system would and should be as designed and properly working. Simple, easy.....and has worked for millions of cars, and still can. My stock system works every time.......no problems.

 

How about posting some pics? Switches fans shrouding etc..

 

 

I posted a picture of the water pump along with the current engine layout. Do both look like they would support a clutch fan? Could you send me a picture of a stock set up?

 

I think the best course of action may be to test the switch. There are many ways to do so but it depends on the tools at hand.

I would first hook up a multimeter to the switch and measure voltage on the terminal going to the fans. Then run the car and monitor the temperature with an IR thermometer. It’s important to validate the temperature with another instrument.

See when it turns the fans on and off and measure the temp at the switch and sensor. If the temp is actually above when the fans should be on, verify that the switch is getting power from the source. If the fans are off but the switch is on, then look to relays.

If you don’t have an IR thermometer, you can pull the switch, connect it to the multimeter measuring resistance and put it in a pot of water and bring it up to boil. Verify that the switch opens and stays opens at higher temps.

From the pics, I doubt the sensor location is the issue.

 

Faulty switch / perhaps it's failing intermittently.
Buy a new quality switch that will turn on at the temperature you feel is best.
Example: 180*F or 190*F or 200*F.
I prefer 190*F (the fans usually turn ON at 190-195*F and turn OFF at 180-185*F)

 

Clean engine!
i would consider getting those fans shrouded so they pull through the radiator, they are probably far less effective as they are..
pic of fans with shroud example..it helps pull air across entire radiator and efficiently

 

can the fans be jumped to run continuously to prove they will cool the engine adequately without adding shrouds? my '59 had the coolant temp monitor mounted at the upper rad hose, and i see Dewitts radiators come with the fan switch mounted to the "end tank". is there a factory bung to mount the fan switch on your radiator, maybe under the upper rad hose?

 

A switch in the top of the intake manifold should be fine. No, there is no provision for a switch in the rad.
most of these thermo switches kick on at a set temp. Say 190. And then don't shut off until they reach about 10 degrees lower that that.
So, you have a defective switch, or a relay that isn't working properly. Most likely a defective switch.
And yes a shroud is ABSOLUTELY the correct way to go.
No need for you to test this. Thousands before you already have.
Ask yourself if you've ever seen a factory built car that didn't have one.
Ask yourself if all these factory's all over the world believe in wasting money on something that just isn't needed.

 

My fans. Note full shroud coverage

See my engine temp switch. Right in front of and to the drivers side of the thermostat housing. Before I installed a computer to run things I had a basic fan thermo switch right here. Never an issue with that.
but believe me when I first went to electric fans I made every mistake one could make. But this is a fine location for your thermo switch.

 

I installed a new ZZ6 turnkey crate engine in my 75. I also have an electric fan setup. Mine works flawlessly. My vote is to sort out what you have vs going back to a mechanical fan clutch.

I have a double row aluminum rad from Champion along with a single shrouded Spal fan.

I wired mine so the fan has power no matter the ignition switch position. On a hot day at max temp with fan running… turn off the ignition and my fan will run about 5 minutes. That single Spal moves a lot of air and I like the idea of it blowing while the engine cools.

I also have an easily accessed battery kill switch so I can shut it all down instantly.

Can post some pics later.

 

If you go to an engine driven fan it will have to be off of a late 80's..early 90's GM truck as it is rotating in reverse.......

As mentioned....skip the switch and wire direct.....see how it cools and if the fans stay on......if they do, then you need a new switch......

Jebby

 

I have no issues keeping my LS cool with a single un-shrouded electric fan. I've noticed even if I leave the fan off, it doesn't get much higher than 190.

The reason I mention this is because we have a similar radiator and fan setup. Sounds like in your case the switch is going bad, and not properly kicking the fans on and off. You can easily replace the switch, or wire it direct so it comes on when the key is turned.

I personally run my fans direct key on. I've never had problems with the car being unable to get up to operating temp in the cold months, and in the summer I dont have to worry about switches taking a dump and the cars getting hot in traffic. Super simple to wire. Use a relay and an inline fuse, and tap the key on power from the fuse box to run to the relay. That way you're not pulling all that amperage straight from the fuse box.

 

My switch is a simple single pole unlike the dual pole on the op’s car in this pic. All mine does is provide ground to the relay when the switch hits the specified temp.

1 wire. Seems much simpler and less failure prone to me.



why the 2 wire system?

 

@michaeljbush here is my ZZ6 cooling system setup.

I seem to remember the water pump on this engine spins backwards or something like that if you’re still considering going to a mechanical fan.

Your intake manifold looks just like mine.



I think the water pump on a ZZ6 spins 180 from a normal small block


keep it simple!


1 wire! 1 wire only!

the op’s manifold looks just like mine

 

My .02?
On my LS swaps I have the ECM control the single 16" Spal fan.
Having said that one of my first LS swaps, a 98 Wrangler I had a NPT bung welded into the lower left side of the radiator tank. Painless kit. On at 205 off at 195. Been flawless for 15 years.
The Painless kit sensor grounds the relay turning on the fan or fans. Since you are running two fans double check the amp draw. You may need two relays.

 

Update:
Will the fans run continuously if the wires are jumped? With the help of a few staples, the answer is yes. I had them running continuously for just under 15 minutes, which is about 5x their best running time. From what I gather from y'all's responses, a new switch may be in order.

Kie asked why the two wires? Yeah! WHY the two wires? Most of the switches I see are one ping only. Uh... I mean one pole. The fans do come on if I engage the A/C. Does that have anything to do with it? I don't know. However, the A/C suddenly stopped working. I haven't tried to use it since the A/C clutch still wants to engage (if I'm even using any of these terms correctly). Meaning, I haven't explored that further.

Can I go to a single wire system? In one of my pictures, I circled two relay switches. I have assumed that both were needed for fan operation. Can I simplify this? Do I need to?

What I didn't find was in-line fuses. Nothing told me I should find them but thought they'd be there. A thought.

 

Edit I read the previous post and answered my own question

 

The switch choice is probably is due to the A/C, so that you can switch the fans in via a positive signal. The same that is used for the A/C clutch.

Thats worth investigating, you would need a diode to prevent back feeding the clutch from the temp switch. Unless you doubled up relays… I’m curious how this was wired.