Midwest Muscle

Hey folks, big thanks to the community here for all the posts about cooling on these 3rd Gens. With what I learned in the Forum, I was ready to put my US Air Force era electronics training and shadetree mechanic skills to use.

Find below things I learned on my unmodified '92 Z28 convertible (5.0 / 5 sp) this weekend. Previous Q&A posts of mine have since been edited to undo things that I found inaccurate once I jumped in and got my hands dirty:

1. Don't trust the temp gauge alone. I thought my car was running the occasional 240'ish in stop and go traffic. Wrong. It's actually running 220 at its warmest. Thinking my car was running hot prompted me to investigate.

2. Primary fan = Driver side. This one comes on (alone) with the A/C switch or when the ECM kicks it on at 220. The paperclip trick (jumping A-B) for turning on the fan instantly when the key is turned to Run was very helpful.

3. Secondary fan = Passenger side. This fan comes on when the temp sensor in the head (between 6 & 8) grounds itself, 238 degrees factory. I thought my passenger fan didn't work, but saw it was fine when I grounded the lead between 6 & 8 cylinders.

4. Try as I might, I could not swap the 6 - 8 temp switch, even though I had a new 215 degree switch (compared to 238 stock) in-hand. Just not enough clearance to get to it, even from underneath, without messing with other things.

5. I like control of the fans, but I don't like a fan running once the key is off. I also don't like over-riding the factory provisions. I want manual, but not manual only! So I opted to make a tweak that allows me to control things w/o breaking any OEM designs. I spliced into the 6 -8 lead and now have a toggle switch inside the car that completes that path to ground when I want it to.

Using a simple 2-position toggle switch now mounted inside, I can activate my passenger fan anytime I like. And if I don't use the switch, the OEM design still works >> Primary driver side on at 220 via ECM, secondary passenger side on at 238, unless it's been changed to a lower temp. With my $5 mod, mine stays right where I want it, 185'ish. Thanks folks for the tips!!

Mike

deadbird

The sad part is, is once this post is half way down the page, people will be to lazy to scroll that far for this useful information because, that's effort. Then it will get lost in the archives for the select few that actually know how you use the search function.

Twin_Turbo

iTrader: (25)

Are you sure the primary fan comes on with a/c?? on all my cars the sec fan comes on as soon as you request a/c

Midwest Muscle

T_T, yeah my primary is driver's side and comes on with the A/C switch. I was expecting it to engage the secondary, but not the case on mine. But with the newly added manual option toggle switch on my secondary, I don't expect that primary to kick on much since I don't run A/C often and wouldn't normally wait until 220 for the ECM to start it spinning either.

db, I know I learn a lot from Forums, so I try to give back a little knowledge when I can. Speaking of that, I swapped my temp sender unit, the single wire to the gauge. The one I took out did not look factory OEM, but was better than the new one I put in. So took the new one out and put the original back in.

The old one shows 240 on the gauge when it's actually 220. The new one showed 260 on the gauge when it's 220. Looks like my gauge might be a bit off, but +/- 10% on a factory 3rd Gen gauge isn't terrible either. So now I think I'm done with all things cooling related. Just didn't like it creeping up to 220 in traffic. I prefer it cooler ...

Mike

Reid Fleming

iTrader: (2)

I'm not a fan of manual fan switches. I prefer a simple fan switch that satisfies summer conditions, winter conditions, while at the same time allows performance and doesn't effect emissions tests. To me, the 200-185° fan switch works perfectly. Off during the wintertime, mostly on during the summertime. Always on in rush hour grid lock. Still keeps the engine at a minimum temp of 185° and is running full blast at 200°. Works well with any thermostat.

I also like that if your car is running at let's say 210°, you can turn the A/C off, and the secondary fan will keep running with the above fan switch. Stock, it would turn the fan off.

Primary fan is on at 223°F (driver side)

Secondary fan (passenger fan) depends on year. The 1987 and earlier cars turn it on only by temperature alone. The 1988 and later cars turn it on based on temperature and/or A/C use . 234°F it's on.

The secondary fan is NOT necessarily on when the air conditioning is on. But it tends to be anyways. Once the A/C high-side pressure goes over 233 psi, the secondary fan turns on. Once the high-side pressure drops down to about 180-190 psi, the secondary fan will turn off (assuming the temperature is below the fan switch point).

I've verified this with A/C gauges as well as driving in cold/hot weather. "Cold" starting the car in summertime (ambient temp of say 80° outside), the car is obviously below it's fan switch temp. Turn the air conditioning on and the secondary fan will turn on and off every 20 seconds or so. I can watch the high-side pressures on my A/C gauges rise and fall with the secondary fan......pressure goes up to 230 psi. Fan turns on. Pressure slowly drops down to 180'ish psi. Fan turns back off.

Driving the car on a cloudy 70° day, I can pull over and pop the hood and the secondary fan will be off even though the A/C is running. Driving the car on a 95° day, the secondary fan will be all the time with the A/C running.

Secondary fan will also turn on the primary fan if it's not already on. With my car running the stock ECM (223° primary turn on) and the 200-185° fan switch, both fans will turn on at 200°.

Midwest Muscle

Reid, good input. I don't like manual only, since it requires too much effort and bad things happen if one forgets. I also had a supercharged '01 Formula with the SLP manual control, and it drove me nuts since it would run (by design) with the key OFF. I eventually changed that since I got tired of going to a 500hp+ car with a dead battery!

I'm not frugal by nature, but I did like spending $5 and a small amount of work on the '92 Z28 this weekend, which allowed me to verify all my factory-style provisions work plus adding user-controlled temp management ... Without worrying about what might happen if I forget about the switch. If I forget it, everything works as OEM designed.

Mike

Reid Fleming

iTrader: (2)

Mike, probably my biggest beef with manual fan switches are the hack jobs that occur waaaay too often. I long ago lost track of how many people show up on TGO wondering why the fan won't work or why it runs all the time. Or the wiring that burns up because it wasn't done the right way.

The other thing is that to me, manual fan switches are sort of like solid lifters. Why not go hydraulic and just let it do it's thing? Now there are some times where a manual switch is handy. Drag racing being the obvious one. Sometimes if you're stuck in traffic and the gauge is reading 220°, doing sometime like stopping for gas might make it jump to 240°.

Many years back, I was driving a 1st gen VW Rabbit (not my car, was housesitting and taking their dogs out to the park). The Rabbit had an interesting deal in that the radiator fan would keep running after you shut the car off. But it wouldn't run for more than about 30 seconds. Less if it was cool outside and you just drove a short way. There had to have been some sort of factory built in timer I'm thinking. Because it couldn't cool the car down that much that quick.

jtsk

iTrader: (3)

Excellent info here guys! I can see that my fans are working as they should. The only problem I have is that my temp gauge doesn't work since I reinstalled my engine after the rebuild. When I turn the key on, it pegs as it should, so I am guessing maybe the sending unit went bad or I damaged it somehow??? Can they go bad just laying in a box for a couple of months? It worked fine before I pulled the motor.

Midwest Muscle

Reid, totally agree on hack jobs. I've bought my share of those - Never again! No worries though, my installs tend to be a bit OCD ... I'm not much for doing anything less than 100%. Even on this simple switch to give me added control over my temps, it looks factory. At least the basics of electronics and attention to detail still apply - If you're going to do it, do it right.

Mike