asianlimodriver

OK, Corvette Forum brain trust. I've had my Dewitts radiator and fan set up for a bit (thinking 5-7 years, not sure). On two occasions now, the electric fans did not turn on when it reached temp. I've checked fused, water level but nothing obvious. Then later, they will work as expected with no issues. Any ideas of what can cause this? I plan on calling Dewitts as I'm hoping if it's the relays or temp sending unit, it's under warranty. I could use some advice related to this issue.

I'm thinking about wiring in a toggle switch that is wired to the accessory fuse. I thought that I'd just splice into the power wires after the relays and put a 30 amp fuse inline from the toggle switch. Any pros or cons to setting it up like this?

Big Block Dave

I would say, before you go and wire up a switch direct from a hot source, I would wire the switch into the ground wire for the relay that was connected to the temp sender switch (assuming this is how it is presently set up).

This way you keep the relay in play and systematically remove variables.. in this case, eliminate the sender first. If you are still having problems, perhaps the relays are bad, circuit breakers are iffy, or the fans are grounded to a poor connection.

Sigforty

Where is the temp sender? Is it in the radiator? I know I bought my setup a while back and they now put a ground wire on the fan shroud attaching screw. This will correct any issues with the radiator not being grounded.

ddsmith60

If this is wired anything like mine, then the switch should be wired from the ground side of the relays to a good ground point. You may have a problem with the radiator ground if you have the temperature sender mounted on the radiator. You can wire one side of the switch to the terminal on the temperature sender and the other side to a known good ground. Run it with that switch off and if it acts up, turn the switch on and see if the fans run. If they do, then you know the temperature sender is bad or it has a bad ground through the radiator.

Bikespace

My dual-Spal fans (via DeWitts) are wired through a pair of always-hot relays (fed directly from the alternator). The relays are switched by two IGN-on wires to the relay coils, which are grounded through a single temp switch (sensor) in the intake manifold. With the IGN on, I can jump the temp switch with a screwdriver, engage both relays, and force both fans to run. This is the simplest I could make it, with a single point of failure (the temp switch), but otherwise redundant everywhere else. I could add a switched ground to either or both relay coils to force the fans on.

If yours is wired similarly with two (or more) relays, I'd suspect the signal isn't getting there. Perhaps the temp switch isn't working because of an air bubble at the top of your engine. My fans only come on at idle, ever. I could drive for hours on the highway without the fans coming on, by design.

I wouldn't switch 30 Amps except through a relay. That is why relays exist. But you can absolutely add a switched ground to the fan relays to bypass the sensor switch and turn them on manually.

Big2Bird

I cannot answer your question since I do not know how you wired it up.

Rescue Rogers

I have DeWitts single fan setup and the wiring that came with it used an in block/head/intake temp sender. If you just disconnect that and go straight to ground the fan should come on. If it does the sender could be bad, but I had the exact same problem and the plug that connected their harness to the fan itself melted and it had a bad connection, not to mention the melted plastic. I have since rewired it and gone with a Deraile controller. THe dewitts relays caused the fan to be either on or off and the instant on created some wire heating issues. THe Deraile controller ramps up and has a cool off feature as well as a separate on off toggle wire. JKippin had a simialr issue and his relay contoller block had melted internally at the relay

ddsmith60

Mine is like Bikespace with the exception of my temperature switch is on the radiator just below the return hose. If you are sporting the dual relay setup and have the temperature switch on the intake manifold it is most likely a bad switch. Like he said grounding the terminal at the switch should turn on both fans.

Richard Daugird

This is why I love mechanical fans...

SteveG75

Dual Spals for almost 20 years. Last couple of years, would have an issue were only one fan would come. Sticking relay. Would tap the top of the relay and it would work again. Replaced with a single Lincoln Mk VIII fan and it cools better now.

4-vettes

after getting caught out far from home with no fans caused by a defective relay. Not only did I replace the relay with a gen. Bosch 50 amp.relay. I wired in a heavy duty toggle switch. said switch rated at 50 amps. fused of course with a 50 amp blade type fuse. bypasses the relay and sends power from starter solenoid straight to fans. flip the switch and fans are running, car on or off. overheating is no joke!

lionelhutz

Do not try to feed dual fans from the fuse box accessory terminal.

As noted, some info on how it's wired would help with suggestions on possible solutions.

What @bikespace wrote about dual relays and dual power and coil feeds is a good way to wire dual fans. Make it hard for a single failure to take out both fans.