GREGGPENN

Many of you know I swapped in a Champion dual 1" radiator last year. I posted a detailed thread on the subject (that included debates on related cooling topics).

On other issue, I didn't like how my aux fan was working. As with the OP of this thread, I found L98's have some complexity for choosing alternative aux fan operation. Specifically, if you buy a 200/on -- 185/off fan from MAM, it may not operate like you'd hoped. That's because cylinder head coolant temps are hotter than thermostat housing temps.

Cylinder head coolant temps in the 190-195 range will be very close to the opening temps of a 180-deg thermostat. IOW, when the thermostat hits 180, the cylinder head coolant is hotter -- by 10-15 degrees. I know because I've measured and seen this happen. Though it's possible mine might have a larger difference (from stat housing to heads) than a 350, the linked thread (paragraph above) indicates 350 owners are likely to be surprised by the difference.

With MAM's 200-deg (low-temp) aux fan switch, you will actually find your aux fan coming on just above the temp where a 180-deg thermostat maintains coolant temps. If you have a stock 195-stat, I guarantee your aux fan will run ALL the time with the MAM aux fan switch. I believe you will find it will run most -- if not all -- the time even with a 180-deg thermostat. That's because the cylinder head coolant temp isn't likely to drop in the 185-deg range. (For that to happen, thermostat temps would need to drop below 180-deg!!!)

After reading some posts in this forum and in the TGO, I finally decided the best option for my 383 is the 14043275 (aka D1855B) made by ACDelco. If you do your own search, here are the specs you'll find for aux fan on/off temps....
AC#14043276 238/on 223/off (This is the OEM stock fan)
AC#14043275 215/on 200/off (IIRC, This was used on SD Camaros)
MAM 609-106 200/on 185/off (This is the Mid-America unit)
(Note: These are the temps you will see on your digital dash display)

In reality (because of the difference between thermostat and cylinder head cooling temps), these switches will operate closer to these thermostat temps....
AC#14043276 228/on 213/off (This is OEM stock)
AC#14043275 205/on 190/off (IIRC, This was used on SD Camaros)
MAM 609-106 190/on 175/off (This is the Mid-America unit)
(Note: These temps are more likely seen by the ECM as it monitors the intake manifold sensor [closer to the stat housing].)

Hopefully, you can see the MAM switch is never likely to turn off. The Camaro switch should turn on in most conditions when the car is moving. (Though it may rarely shut off in the hottest climates). The stock switch will come on when at rest on hot days AND will normally shut off when moving -- even on hot days.

FWIW, some people believe it's bad to run your aux fan ALL the time because it may raise the load on your A/C unit by raising the condenser temps. (I don't have an opinion on this though. If true, you may have "less cool" A/C air.)

If/when you find yourself doing searches on the subject, you may find this thread, which states the middle sensor is the same as a (AC) D1855B and an (AutoZone) SW505. But, I became suspicious when I found post#5 of this thread. While most people would assume this is a Chinese junk issue, I looked a bit more. When I used the ACDelco cross-reference facility, I looked up the SW505 switch. And, I found it to be equivalent to the 14043276 (FACTORY) switch.

So, don't buy an AutoZone (or any other) SW505 switch -- if you want lower-than-factory on/off temps!!!!

For my own issue, I want on temps in the 215 range with off temps in the 200 range. (Thermostat readings will show 205ish/190ish -- though the display with correctly show 215/200 operation. That's because the dash display uses a different sensor ALSO mounted in the (PS) cylinder head.

Today, I ordered a BWD TFS 4 aux fan switch (from Advanced Auto). I believe BWD is a Standard Ignition sub-brand but, more importantly, this switch appears to be the same as the Delco D1855B/14043275. At $12 vs. $28 from the dealership, I hope it works correctly. In my searches of this and the TGO forum, I believe it should.

Hopefully, this will help anyone else looking for alternative operation for their aux fan switch.

Bullseye54

Thanks for the #'s.I was in the shop messing with that issue last night.I have an 85 & I want the 215/200 switch myself.I am going to change the relay wires so the aux switch turns on the main fan & the ecm turns on the aux at 228.Rock auto shows TS85 ($10) as the Standard # for Delco D1855B/14043275.I went through the thermostat/switch overlap deal on my 68 GMC last year.An adjustable switch solved it on that.Not the way I want to go on the 85..........Bob

GREGGPENN

I saw the TS85 as well. Forgot to mention that.

In the Delco online interchange catalog,
the SMP TS85 crosses to the higher D1852B (228-deg) switch.

I have no way to confirm/deny the online catalog...just thought I'd point out what I found.

SunCr

"FWIW, some people believe it's bad to run your aux fan ALL the time because it may raise the load on your A/C unit by raising the condenser temps. (I don't have an opinion on this though. If true, you may have "less cool" A/C air"

No - it lowers the temp/pressure which needs to avg about 200 psi to flow something around 25 to 32 psi through the Evaporator. Keep the high too low and the Low Pressure Switch won't have enough oomph to keep the contacts closed and the compressor shuts off. So yeah there's no cool air, but realistically, it really begins to effect operation at lower outside air temps where it might be nice to at least keep the windshield clear.

A mobile a/c system needs to maintain something around a 100 degrees in the Condenser and by doing so, Idle/Low Speed Coolant Temps will be 10 to 20 degrees less with it on or it isn't working right. That's well below any reasonable number for Coolant Temp which is one of the reasons it needs a thermostat and that's why the Condenser sits in front of the Radiator.

The real bitch with dual fan operation (on these early years) is the electrical draw can easily exceed alternator output at idle with all accessories operating. Once that happens, the fans slow down and it overheats (coolant and what's in the Condenser) - and there goes the a/c along with all the other bad things that can happen.

Bullseye54

OK I just ordered the Delco D1855B/14043275 from RockAuto ($20).I'll let you know what the on/off is on the stove & an accurate thermo.
SunCr,I wanted the main fan to stay the main fan so I'm wiring it so the aux switch opperates the main fan relay,whitch will turn on 1st & the aux will come on at 228 by ecm.Its an 85.......Bob

TTOP350

Also do some checking on the 89 TTA fan switch. It may have some numbers your looking for. I'm thinking its the same or close as what your calling the SD camaro.

oldalaskaman

excellent write up Gregg, converting my C3 from manual to electric fan(s) tomorrow and this is info I was curious about and will put to use, many thanks, bob

GREGGPENN

I should post back to this thread regarding the performance of the BWD fan switch.

Mine comes on around 215 according to the dash display. It goes off right about 200. This means it operates in a range somewhat above where I hoped/expected but it's a range I'm much more happy with. (At the thermostat, this means it's performing more like a 210/195 stat.)

Again, my car is modified with higher compression. Mine won't tolerate quite the temps of a stock motor. Through dyno testing, I determined 220ish is where I start to encounter detonation. So, keeping my temps below that is desireable -- to avoid the need for backing off my [peak] total timing curve.

I'm planning on swapping to a higher CFM fan by next summer. Since I'll be pushing temps that cause detonation in the summer, I'll want to pull idle temps down ASAP. More air from the fan is what the doctor prescribes.



EDIT: To be clear, this BWD 4 fan switch is perfect for people running a 180-stat. If you're running a 195-stat, your fan would run too often (just like the MAM switch).

GREGGPENN

Last week, I ignored the conclusion I made in this 2012 post. I shouldn't have. I ordered the MAM coolant switch to see if there was a chance it would run in the same range as my main fan....or just a HAIR above.

I have my main fan programmed to come on at 188 and off at 183. According to my dash guage, it comes on in the mid-to-high 190s. I never saw it go below 188 yesterday -- which was a hot 95 outside.

With the MAM switch installed, the aux fan came on earlier...at 186 according to my dash. IIRC, the ECM "sees" temps from the sensor in the front of the (L98) manifold. But the dash (and the aux fan switch) are measured at/in the cylinder heads. When I wrote this thread in 2012, I had been datalogging (which driving) and noticed the discrepancy between dash/ECM temps. That's how I concluded what was written above AND posted in the OP.

Since the MAM coolant fan switch was listed having 200 on 185 off, I had hoped for the numbers I posted above. I had HOPED the aux fan would operate a couple degrees ABOVE my main fan. Before ordering, I asked a salesperson if they'd had any feedback on the actual on/off points as observed by consumers. Because I was told it operated right at the advertised numbers, I ordered on.

Problem is the switch came on too low. It triggered below my main fan -- even though my fan is ALREADY LOWERED from the factory settings. Without running a new scan, I'm going to assume temps would never get low enough for the fan to turn-off -- even with a 180-stat!

I let MAM know I didn't think the switch was useful for anyone not running a 160 stat (which is rare). They said they would refund my purchase and appreciated the feedback.



The main reason I broke down and tried this switch is because the replacement TFS4 switch I just bought wouldn't come on. I installed it with copper anti-seize, then again dry. I let the engine run all the way up to 228 (according to dash temps). To me, that means head temps were into the 230's. Even if it comes on higher than 228, that's not what I'm looking for.

Either the TFS4 is defective OR their turn-on ranges are less reliable? According to the Borg Warner book, their turn-on range is listed as: 213-231. That's a WIDE range. In one sense, it seems unacceptable....or at the very least a bit unpredictable.

I suppose I'll buy another and see what happens. It's either that or wire the aux/main fans together.

In another recent thread, I proposed the need to upgrade my fan. While I drained and filled the coolant (several times) testing these switches, I noticed the need to mildly rev the engine to LOWER water level in the radiator. Maybe my "high-volume" PRL water pump isn't so impressive after all? That's what I installed in my 383 build in 2010.

I suppose an electric water pump would be another option.

Cliff Harris

One thing to keep in mind on an L98 is the coolant flow path. The water pump pushes the water into the block in the front and it basically circulates around the cylinders until it reaches the back of the block, where it's forced to go into the heads. Then it goes forward through the heads until it reaches the front water passage in the intake manifold. That's where it goes to the thermostat and then to the radiator.

GREGGPENN

So, do you think the discrepancy in temperature as seen by the ECM vs the Dash is due to sensor variation/calibration?

Joe C

could be and most likely. we've seen around 300° "dash indicated (son indicated - )" on my 85 L98 after loosing coolant. i'm thinking that temp would destroy the engine, but that temp didn't seem to have any ill effect on the engine. I ran a compression check shortly after that, that and the readings were near textbook. drove the car another 5 years or so, before pulling the heads for a valve job. both heads were within flatness spec. either the dash has a discrepancy, or the iron head L98's are truly bullet proof!

WVZR-1

You can buy switches/sensors with different engineering tolerances. Those used for ECM/PCM control are produced with much tighter tolerances than those used for analog gauge display.

As a matter of "testing" you could I imagine remove the gauge sender and substitute with a ECM CTS, jumper the leads from the ECM CTS to the device now in the head and "COMPARE" using a scanner.

You could also check the calibration of the dash gauge to see just what it's actually displaying. The numbers are in all FSM diagnostics.

I believe I know a fellow who has a two terminal CTS in both cylinder heads of his car and monitors both.

There are I'm sure switches with much tighter tolerances for fan control (open/close) than those sold/used for very generic automotive service. Fan control by switch/sender hasn't been widely used in automotive control for years.

ddahlgren

If you talk to Battee (sp?) that does the dash repairs he commented to me the dash analog gauges are very poorly calibrated and said he had seen many marked from the factory as having a problem. I would not have all that much faith in them to be honest. If they are capable of +- 3% new they are not near that now as witnessed by bad tch issues.

GREGGPENN

jfb posted (a couple years back) that cooler water can mix with the coolant that's traveling up the front of the motor....meaning that coolant is likely to show a hotter temp at the rear of the heads.

steven mack

They do make rheostat fan switches that you can adjust to what ever temp you want.

mr-natural

GreggPen back 2.5 years ago you said the following:
I have my main fan programmed to come on at 188 and off at 183. According to my dash guage, it comes on in the mid-to-high 190s. I never saw it go below 188 yesterday -- which was a hot 95 outside.
How do you program that in?

GREGGPENN

Not sure if you're asking how to change the outdoor stat? Hey God! Turn down the outdoor temp!!!!

Or...if you refer to a difference between water temp in various places inside the motor....versus the gauge.

Or...Most likely how to program fan temps? Since you didn't mention year, I have to guess on that too? Are we talking about your 58?


Short answer: I ran a 160 stat for awhile though I'm back to a 180. Changing turn-on temps has to be flashed on LTx cars (computer) or controlled via new "piggy-back" chip in L98s. The computer is up under the passenger dash. Moates sells a piggy-back board that replaces the stock chip. Using software (i.e., TunerPro), you can "burn" a chip in Moates "Burn 2" chip burner. It's a simple matter of typing in the temps (within TunerPro), burning the chip, and plugging in the new chip. The hard part is pulling the ECU from the dash. Later cars are easier because the ECU is under the hood, accessible, and flashable.


Or...You could call Stephen Colbert and ask him if he can put in a good word with God -- to lower outdoor temps.

Or...Everyone could lower their carbon footprint, reduce man-made pollution, and wait for the Earth to cool. When you get under the dash of a C4, this CAN seem like the simpler option!

mr-natural

Dah, how come you don't know what I'm thinking. It's very obvious to me anyway. So since my mental telepathy is low on battery power here's the facts. 87 L98 in a 58. I've located the ECM behind the right side kick panel so it's easy to get to. But from what I understand you to be saying it's either program or different switch. The port below 6 & 8 cyclinders I'm using for the 58 temp gauge. The port between 1 & 3 holds my CTS which I'll probably change soon to a lower temp unit. So that leaves sticking the bulb of a thermostat somewhere and I tried that sometime ago and was not happy with the result. So reprogram seems the available option unless I'm missing something. Which brings up the issue: Do I need someone else to reprogram or is that something I could do. I have a functional knowledge of electronics but haven't worked in the field since USAF days, and that was only 10 years after my car was build.

GREGGPENN

I'm not as hep to the 87 electronics but here goes....

My 89 also uses the 6/8 switch for the dash gauge. The CTS should be at the front of your intake NOT below 1/3 cylinders. Earlier L98s might use that switch (below 1/3) as the main fan turn-on/off. Even if not, it's possible to use it -- in lieu of the computer IF you don't have an aux fan (normally positioned in front of the radiator).

So...I'm wondering if that 1/3 switch is what controls your fan? If so, that's not "programmable". You select one of the desired range and screw it into the block. It "closes" at temp and grounds your fan to the engine block....then opens to shut it off.