CalOhio86Z

Hi all,

I apologize if this perhaps weird question has been covered already. I looked at the "Cooling" sticky and related messages and hope I didn't miss it.

I have a 350 Goodwrench engine in an '86 305/carbureted Z-28 from California ("G" engine code). The swap was done by an Ohio Chevy dealer in 2002 and was done well, I believe, and all smog equipment was retained. Recently, I learned that my cooling fan is not coming on when the air conditioning is off. I understand there is a coolant temp sensor, which on my car is mounted in the thermostat housing. However, my reading of other threads here shows there's also a "cooling fan switch" on the passenger-side head between the number 6 and 8 plugs, mounted low enough that it's hard to see from above.

Tomorrow I'll be jacking up the car to (1) find the cooling fan switch to make sure it's in fact there, and (2) ground it (as per my Haynes manual) to see if the fan comes on. MY QUESTION: what are the respective roles of the coolant temp sensor and the fan switch? I know the coolant temp sensor connects to the ECM to send temp readings, but doesn't the ECM itself turn on the cooling fan once it gets a "hot" reading from the sensor? In other words, why is a "cooling fan switch" necessary if the cooling temp sensor working with the ECM turns on the fan?

Alternatively, does the coolant temp sensor have nothing to do with the fan, and it's only the coolant fan switch that turns the fan on when the critical temp has been reached?

Thanks!

Jon

sofakingdom

iTrader: (1)

Coolant Temp Sensor = tells the ECM what the coolant temp is

Fan switch = turns the fan on

The ECM in a carbed setup is not connected with turning the fan on, in any manner way shape or form. So yes, you're right about that.

CalOhio86Z

Thanks!

TheScaryOne

iTrader: (3)

And the switch is just a heat-sensitive variable resistor to ground, which I believe is about the same for the sensor, as both look identical, it just seems that one has a hot wire coming from the ECM and a second wire of whatever value heading back to the ECM. The switch only has one wire that when grounded turns on the passenger side fan. My connector for the switch was broken, so I can just tap it to bare metal and turn the fan on. Not very useful, but entertaining.

CalOhio86Z

Thanks for the further info!

I did the "ground the connector" test, and my factory single electric fan came on, so it was the switch. The switch is now replaced, but the car runs considerably hotter than it does when the air is on. I had the switch replaced at the local Chevy dealer (too hard for this old creaky guy to get a wrench up there), and took it back into the dealer after driving it for a bit, pointing out the temp difference with the air on and the air off but the fan kicking in.

Perhaps it's the fact that with the air conditioning on, the fan's on all the time AFAIK. With it off, the fan only comes on when the critical temp is reached . . . (or not--I hope to find out tomorrow).

TheScaryOne

iTrader: (3)

Is your primary fan coming on? It should come on before the secondary, unless you have an '87. The primary comes on at 180, I believe, and the secondary at 230 OR when the AC is on. My fan relay (for the primary) just died after many years of use. Replaced it and everything is good again.

Stephen

iTrader: (12)

What's different about 87s? I think both of the fans on my GTA, are key on=fan on, regardless of AC. Dunno who changed what, to do that. It doesn't over heat, so I haven't paid much attention.

sofakingdom

iTrader: (1)

No, not exactly.

The switch is just exactly that - a SWITCH. It's a set of contacts, just like the thermostat that turns on the air conditioner in your house: when the temp reaches the set point, the contacts touch, and operate the relay that sends juice to the high-power elements in the system (the fan motor, in th ecase of the car).

Very different from the sensor, which is in fact a variable resistor, whose resistance decreases as the temp goes up.

Nothing is "different" about 87s, as such; whatever system they have, whether the dual or single fan, works the same as that same system in any other year.

Yes it's typical for the car to run hotter with the AC off AT IDLE, because the temp has to get up to the switch's operating point (230° or so) before the fan comes on. The temp will rise, the fan will come on, it will cool the motor, the fan will shut off, the temp will rise, .... over and over. Driving faster than about 30 mph, however, it should stay pretty much at or just slightly above thermostat temp.

CalOhio86Z

I have a single-fan setup. I've owned the car since new (bought it off the showroom floor on December 9, 1985 at the then Baher Chevrolet in Northridge, California), and it's always only had the one.

TheScaryOne

iTrader: (3)

In the Dual fan setup in 87 the primary comes on with AC, not the secondary. Other than that, roles are identical.

Sofa, I'm not too sure how the thing works, but I can tell you this, to get the part I needed I had to buy all three sensors, and all three look the exact same, with different connectors. I might be wrong, YMMV.

Cal, I thought you had the dual fan setup. Odd. With a single fan setup, the passenger side switch was usually eliminated, and the fan was controlled by a relay and the ECM. Check to see if there's another fan connector in the fan wiring harness. If there is, swap it with what you have in there. To my knowledge, the temp switch turns on the fan at 230, which is why you're running hot.

If there's not an extra connector, then just swap out the switch you just installed with the low-temperature version, available at CSK Auto or Pep Boys.

CalOhio86Z

Thanks, man. I think your suggestion of another, lower temp switch is the way to go.

It's definitely a switch that controls the fan in this car. I'll hang onto the 230 degree one that was just installed for a bit, and I think that I may go with William Weissman's pointers on installing a manual override switch inside that will allow me to turn the fan on manually during really hot days (see https://www.thirdgen.org/cool). Then at some point I'll switch over to a lower temp thermostatic switch for the fan. I'm not thrilled at the prospect of drilling through the firewall to pass the wire for the switch, but it's probably worth it.

Stephen

iTrader: (12)

What would give the best results...

lower temp thermostat
vs
lower temp fan switch?

Turn the fans on sooner? or lower the water temp quicker?

TheScaryOne

iTrader: (3)

There's plenty of holes in the firewall for wires. Just tuck it in somewhere. If you don't be sure to use a grommet!

Well, in his setup, he definitely needs the lower temp switch, and if you go lower than a 180 thermo you should really adjust the switch lower. It's more of a relationship than an either or. But hey, if you do them one at a time, let me know. I'd love to hear your experience. :yes:

ChampionN84

There is great info being past around today! Thanks also doesn't anyone have the part number for the Fan switch for a 305

TheScaryOne

iTrader: (3)

DR137W should be the low temp, DR137S should be the high temp. Can't verify that, I'll have to check the computer at work. But it's Niehoff DR137 something. The DR137S cross references to ACDelco 15-4315

Shred

I think my fan switch packed it in, the fan runs all the time as soon as i turn the key, and it turns on when i ground it. the switch is located drivers side of the block, single wire. gotta get that replaced. what part # from neihoff or whatever has a single wire sensor? Also, what do i gotta rig up so i can have my fan switch as well as make my coolant temp gauge work again? if nothing else i could get a cap with a gauge in it from mr gasket

TheScaryOne

iTrader: (3)

Driver's side sensor goes to the gauge in the dash. Passenger goes to the secondary fan. Under the coolant neck goes to the computer, which controls the primary fan.

dustpusher

Would also like a part# for low temp switch.Thanks for the info

TheScaryOne

iTrader: (3)

Four posts up. Jeeze. Can't even read the thread, can you?

Also, for future reference.

229---------------DR137S
215---------------DR137W
204---------------DR137X

dustpusher

I did read the thread you said you had to verify the numbers.Anyway Thanks for the part numbers.

KYLE87

iTrader: (5)

I have two sensors going to the coolant neck, I know one is the coolant temp sensor, but what is the other??

govenorcamaro

iTrader: (2)

hey camaro punk what kind of car do you have I also have two sensors going under the waterneck mine is a 87 iroc-z 350 tpi auto

Aaron_SK

iTrader: (1)

If you have TPI you will have a second sensor for the cold start injector. IIRC it works independant of the ECM to trigger the cold start when the temp is low enough.

It's pretty easy to tell them apart. The coolant temp sensor looks like every other GM temp sensor, but the cold start sensor is larger, and has a spring clip on it similar to the injector connectors.

Don't know what camaropunk has in his unless his engine was swapped from TPI, and not an LG4.

TheScaryOne

iTrader: (3)

Ah. I think the cold start was removed halfway through '87, so I was wondering what sensor he had that I didn't. :P

Aaron_SK

iTrader: (1)

Hmm.. I always thought cold start wasn't taken out till '89. Did you swap out your intake?

KYLE87

iTrader: (5)

No, its an lg4 with a 1 fan setup and there are two sensors going to in to the waterneck. Im wondering if possibly they put my fan switch there instead?

Aaron_SK

iTrader: (1)

I'll admit I don't know much about the LG4's. Do you have a temp sensor in the passenger side head? That's where the fan switch usually is in TPI cars.

KYLE87

iTrader: (5)

According to what ive read I am suppossed to but i cant see it from above and where i live now I cant jack it to get up under there.......Here are some pics of the sensors if that helps


Attachment 447524

Attachment 447525

ems2357

where is this located 89 camaro 305 TBI

sofakingdom

iTrader: (1)

Yellow & black wires = coolant temp sensor

Other one (vacuum lines only) = thermal vacuum switch for EFE valve