Crumpler

So I was sitting in stop and go traffic on a hot and humid afternoon. I noticed (because I'm paranoid) that my temp gauge was climbing up slowly. She usually runs at the first hash if she is moving and can get half way to the second hash in the summer in a slow moving traffic snarl. Belt driven fan replaced with electric, 16 inch Spal, which runs off coolant temp sensor in radiator hose with setting 185 F.

So I see her hit 3/4 and I'm waiting for the auxiliary fan to kick in and save me because there's no end in sight for the traffic. I then see the gauge needle starting to tick and drops to zero -- with several sweeps back up to 3/4.

After crapping my pants-- I got off the highway and checked everything. Seemed fine and ran at 1/4 hash for the rest of my three hour trip at 80 mph on the highway. I do have water wetter in system.

So first question: When does the auxiliary fan actually come on? What sensor controls it?
Like some other S3 guys, I have jumped it and validated that it is operational.
It does not power on automatically when a/c is on.
I have heard, but not validated, that it does kick on at 3/4.

Second question: My primary cooling fan is electric already. What's the downside of wiring power off that to secondary fan? In that, both fans run whenever coolant temp over 185.

Thanks ahead of time.

WallyP

The earlier cars have a pretty poor control system for the aux fan.

The Temp control is OK if functioning as designed.

The AC control of the aux fan sucks - there is a temp switch mounted on the stem sticking up on the receiver/dryer, so the fan kicks on when the Freon gets hot enough to trigger the switch.

I much prefer a system where an added relay is installed that is triggered by the HVAC controller turning on the AC compressor, and that added relay also turns on the aux fan any time that the compressor is running.

davek9

The S3 Aux Fan is also triggered by a Temp Switch on the Intake, if the intake temp gets Heat Soaked (rarely happens) the hood also needs to be closed and or jump the hood safety/alarm switch when testing.

Usually the Aux Fan is triggered via the Temp switch in the Left Rad side tank or as Wally said only when the Freon Temp gets hot while AC is running. This is not the recommended way to run the AC fan with R134 as the heat curve is not as gradual w/ 134 as it is w/R12.

Any additional electric Fans should be wired to the Jump w/ an in line fuse and supporting relay.

hope this help,

Dave

The Fixer

Dave,

in my old Jag i used to own i had my aux electric fan switched inside the cabin.

i'd just flip it on in traffic scenarios like you describe (worst feeling btw) and watch the temps drop.

also it can never hurt to carry one of the mini IR temp devices on the market with you when your gauge acts up.

i found a really good one at Hobby Town USA (my Son has a nitro fuel RC 4x4)
they are about 1" x 2.5" x .75" in size and about $25 and very accurate.
i keep one in all my glove boxes.
They are used by nitro fuel RC hobbyists to determine mixture while running them, extending their tiny high revving air-cooled motor's lives.

Crumpler

Thanks you guys, for your time and the awesome help. It means a lot to be to be able to get some veteran support.

Matt, that's a cool idea. I like the concept of being able to control when I use it.

Dave, I have new temp. sensor on intake, but have not jumped hood safety to see if operating at pig roasting temperatures like the other day. A/C function is questionable so I have not been using.
I do have dedicated in line fuse and relay on primary fan, would I be okay running both fans on that?

Wally, appreciate the feedback. My Plumley "De Re 928" was the first thing I think I ever took the time to put into it's own binder.
It's pretty beat up now, and covered in oil fingerprints, but I still use it consistently.

Regards.

missile2511

I am old school. I put a switch on the dash to turn on the secondary when needed. The fan was 24/7 so I simply bypassed the auto feature.

The Fixer

^

Dave,

my Jag's electric fan was set up with a temperature switch,

but i could override the switch like the gentleman above from inside the cabin.

That is a nice set up.

dr bob

Strolling through the WSM's on the way to finding something else, I cruised through the section on testing the thermostat. It reminded me tha the thermostat is't expected to be full open until 210º or so. I know we all get our butt muscles clamped up when we see the gauge move off any higher than 180º or so, but it really is OK and in fact perfectly normal for the car to occasionally run at 200º+ on hot days.

My 'new' Honda Pilot has OBD-II diagnostics available, and you can't let an opportunity like that go to waste, right? A bluetooth reader plugs in, and links to my tablet for datalogging, diagnostics, and the ability to display a LOT of parameters in realtime. One of the more interesting is coolant temp. The dash gauge is very consistent, stays at the low side of midrange, well away from any warnings. It doesn't seem to be affected by much, including changes in load, road speed, AC operation, etc. Meanwhile... The ECU shows coolant temps between 185º and 215º, a 30º normal operating window. Like the 928, the fans speed up and slow down to stabilize temps, but their operation is purely reactive. They cycle speeds based on coolant temp at the engine.

Meanwhile the 928 runs fans to stabilize the temp of the coolant returning to the engine, so the mechanical thermostat can regulate circulating temperatures within the engine. We watch that internal temperature carefully, and sometimes wonder why the fan opertion is a little out of sync with what we see on the gauge. Meanwhile, it seems many add-on fan conrollers want to read the engine outlet temp. That's to let you gear the fan cycle more I guess. Reading and responding to return temps makes a lot more sense to me.

Crumpler

Follow up on Aux. fan.

To avoid certain death this summer in traffic, and have a failsafe back up, I kept moving on the fan.
I ended up running a switch into the cabin, with in line fuse and relay.
The only place it didn't look jinky was next to my wideband gauge.
I confessed to a fellow 928'er, that for some reason it reminds me of the old Adam West batmobile.
Was that a jet or a rocket motor?



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