Mark VIII Fan Relay Size?

[ZephyrEFI]

So, I've decided to add an oil pressure switch to my Mark VIII fan with DCC controller. I wanted to get my fan to not continue running after the engine is turned off. It does that presently, but not for too long. I messaged the company, but didn't hear anything back, so I assume they must be defunct or something, so any solution is going to be up to me to figure out. Looking at the wiring for the DCC controller, there is nothing that tells this thing whether the engine is running or switched power is turned on, or anything. Maybe it can draw its own conclusion based on the radiator temp sensor starting to see a decline in temp to tell it the engine is off or something; I don't know. And the company was always pretty mysterious, so we may never know. There are a bunch of unused pins on the controller, I have no idea what they do.

ANYWAY, the oil pressure switch will go to a relay that will cut the power to the controller when the engine is off. The Mark VIII fan is notorious for pulling a crap ton of amps, but the DCC controller uses soft start and stop to mitigate that. So that leads me to my question. What amp rating relay would you use for this? I remember my old Dakota Digital controller used 75 amp relays, maybe in parallel or something I don't remember for sure.

[Broncojunkie]

Pardon my ignorance, but why is the fan controller not triggered by switched power? Is there a reason you need to have it triggered by oil pressure switch as opposed to regular key-on?

[ZephyrEFI]

Pardon my ignorance, but why is the fan controller not triggered by switched power?

Good question, I have no idea. I just followed the directions to wire it. I've heard that previous versions of the DCC PWM controller used a switched on circuit, but apparently from the FK-45 onward, they don't.

Is there a reason you need to have it triggered by oil pressure switch as opposed to regular key-on?

I just thought I would because I was adding an oil pressure switch to turn on my stupid hyper-sensitive Innovate wideband to make sure it doesn't fry itself if I wait too long between turning on the key and starting the engine.

[Broncojunkie]

Ah. Ok. That all makes sense lol! I can't remember what brand my wideband is. Thankfully, I haven't had issues with it being hooked to switched power. Maybe it's something I should be worried about.

I do recall talk of an oil pressure switch. I believe it was a discussion about electric fuel pumps and racing. In a crash, the lack of oil pressure would ensure the fuel pump would shut off. I've been meaning to look up that thread so I can work on adding that feature to a couple builds. Anyway, the same switch should do what you're wanting.

[Broncojunkie]

Here's an example of an oil pressure safety switch that should do what you're wanting. There are 4 or 5 different examples on Summit's site (Holley, Mr Gasket, etc)
https://www.summitracing.com/parts/crt-a68301

[massacre]

Ah. Ok. That all makes sense lol! I can't remember what brand my wideband is. Thankfully, I haven't had issues with it being hooked to switched power. Maybe it's something I should be worried about.

I do recall talk of an oil pressure switch. I believe it was a discussion about electric fuel pumps and racing. In a crash, the lack of oil pressure would ensure the fuel pump would shut off. I've been meaning to look up that thread so I can work on adding that feature to a couple builds. Anyway, the same switch should do what you're wanting.

To turn off the fuel pump in event of an accident, i just installed a stock Ford "inertia switch". Mounted in the trunk, wired between the fuel pump relay and the fuel pump itself, any significant impact will kill power to the fuel pump. Readily available, cheap, and easy to wire in.

Never heard of an oil pressure activated fan, but it does make sense. I do have a Markviii fan stashed away, i know the stock Markviiis had a CCRM that controlled the fan, and that they were prone to many problems. I am using a black magic 185 fan now, operated by the Terminator X. With the Holley, the fan can be set to only turn on over a certain RPM, say 500RPM so that it will not come on KOEO.
Not sure what you are using for tuning, but could your fan parameters be set in a similar way?

[gr79]

Chevy Vegas had that switch setup.

http://wallaceracing.com/electric-pu...oil%20pressure.
https://documents.holley.com/199r9680-1rev.pdf

[ZephyrEFI]

Yeah, I have the inertia switch still in my stock '90 chassis harness. I'm not concerned about fuel being a problem.

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[OX1]

So, I've decided to add an oil pressure switch to my Mark VIII fan with DCC controller. I wanted to get my fan to not continue running after the engine is turned off. It does that presently, but not for too long. I messaged the company, but didn't hear anything back, so I assume they must be defunct or something, so any solution is going to be up to me to figure out. Looking at the wiring for the DCC controller, there is nothing that tells this thing whether the engine is running or switched power is turned on, or anything. Maybe it can draw its own conclusion based on the radiator temp sensor starting to see a decline in temp to tell it the engine is off or something; I don't know. And the company was always pretty mysterious, so we may never know. There are a bunch of unused pins on the controller, I have no idea what they do.

ANYWAY, the oil pressure switch will go to a relay that will cut the power to the controller when the engine is off. The Mark VIII fan is notorious for pulling a crap ton of amps, but the DCC controller uses soft start and stop to mitigate that. So that leads me to my question. What amp rating relay would you use for this? I remember my old Dakota Digital controller used 75 amp relays, maybe in parallel or something I don't remember for sure.

Supposedly two different Mk VIII fans, with the earlier version being almost identical to the Taurus fan.
Anyway, this is what I measured off Taurus fan back in the day.

"Taurus fans draw 62 amps startup and 23 amps full speed continuous
(I measured them both back in the day)."

I also run one of the older DCC's with dual Taurus fans on my FSB Rock Crawler.
I would think you should be Ok with a 30 amp relay due to soft start, even with the better MK VIII fan.

[ZephyrEFI]

Cool, thanks. Yeah, I'm pretty sure mine has a '97 part number on it.

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