Another Oil Cooler Question

sigchuck · 07-11-2019, 06:23 AM

Hi guys, I've assembled the majority of the parts I need to add a Carrera cooler to the front well of my 1983 SC.

I'll be using factory parts, aside from the temperature sensor, fan, and wiring.

I went with the two prong BMW sensor and a SPAL fan and relay set.

My question relates to the relay wiring - there is a single wire for the sensor, but the BMW switch has two prongs. Is one prong simply not used, or do I need to ground it to the body? Does it matter which prong is used and which is empty/ground?

Thanks for your help! The number of posts on the oil cooler upgrade have been extremely useful in preparing for the project!

HaroldMHedge · HaroldMHedge's Garage

You will need to ground the second prong to the body and it should not matter which is used for the ground.

911pcars · 07-11-2019, 08:23 AM

Post a sketch or equiv of your proposed circuit. From your brief description, unable to confirm. Avoid releasing the smoke.

Sherwood

Targalid · 07-11-2019, 08:39 AM

If you want to see it work first, set it up on a table top with a battery and test it.

1979-930 · 1979-930's Garage

The safest way to wire the sensor is make it a ground trigger for the relay so no power positive power runs through it.
So you’ll have two hots to the relay. Triggered power to the fan and the temp switch will ground the relay and activate power to the fan.

Sent from my iPhone using Tapatalk

sigchuck · 07-12-2019, 05:56 AM

Guys, attached is a wiring diagram that came with the relay. I would prefer to avoid wiring anything directly to the battery, but in looking at the relay and diagram, I'm not sure that will be possible since the relay is in a weatherpak type box that's pre-wired with what you see in the diagram (meaning only the 4 wires (yellow, orange, red and gray).

Any thoughts on making this work with the 2 prong switch (and via the frunk fuse block) would be very much appreciated!

FWIW, I don't plan to run any sort of a manual override switch. Thanks!

86 911 Targa · 08:06 AM

Quote:

Originally Posted by sigchuck

Hi guys, I've assembled the majority of the parts I need to add a Carrera cooler to the front well of my 1983 SC.

I'll be using factory parts, aside from the temperature sensor, fan, and wiring.

I went with the two prong BMW sensor and a SPAL fan and relay set.

My question relates to the relay wiring - there is a single wire for the sensor, but the BMW switch has two prongs. Is one prong simply not used, or do I need to ground it to the body? Does it matter which prong is used and which is empty/ground?

Thanks for your help! The number of posts on the oil cooler upgrade have been extremely useful in preparing for the project!

^^^^^
As per my recent post, I used this.

Have a look.

You will have to add a relay to the fuse panel.

Best,

Gerry

47silver · 47silver's Garage

oopos sorry wrong post

911pcars · 07-12-2019, 11:28 AM

The diagram includes a relay, although not identified as such. The diagram also shows an optional ON-OFF circuit switch that sigchuck chooses not to use. I assume he's connecting to a factory two-prong ON-OFF switch? One less switch to install.

However, that "sending unit" is a coolant sensor, most likely not calibrated for an external oil cooler, thus of questionable accuracy in this application. Do you know the preset tip in (circuit close) temperature? There are aftermarket, user-adjustable, radiator attached sensors/thermostats (e.g. Hayden). Even the factory oil cooler sensors are reported to be set at too high a temperature - BMW equivalent sensors have a lower ON temp. Maybe someone can chime in with a description of the temperature differences.

Quote:

My question relates to the relay wiring - there is a single wire for the sensor, but the BMW switch has two prongs. Is one prong simply not used, or do I need to ground it to the body? Does it matter which prong is used and which is empty/ground?

See the switch in the diagram? That looks to be equivalent to the factory switch you referenced. Simple ON-OFF switches open and close the electrical path in a circuit. Connect as shown while acknowledging the caveats described.

The electrical diagram shown is a pictorial current path drawing. As such, you want to avoid an octopus-like gathering of ground (or source) wires at the battery. The ground connection can be at any chassis location, ideally near a shared factory ground post instead of random locations. However, a clean metal contact is equivalent and acceptable. Keep it neat and factory-like as much as possible.

Sherwood

sigchuck · 07-12-2019, 11:47 AM

Sorry, this is just the diagram that came with the relay. I am using the BMW replacement switch that's often used in lieu of the factory switch as it has a lower "on" temperature. It's a two pole switch as opposed to the factory single pole.

I think SPAL does sell the relay set with a sensor (coolant, not oil), but I opted for one without. Perhaps it won't work for this application, but it would be great if I could make it work!

Steve Marshall · 05:39 PM

If the two prong switch is normally open, it is wired between the ignition wire and the relay. I.E. the orange wire. That way when the desired temperature is reached the switch closes, completing the circuit and firing on the fan. Or, wire it in the gray wire and ground it in lieu connecting it to the sensor which you don't have. Either of these configurations should work.