I have an '88 all stock motor and cooling system and concerned about the cooling temps on hot days sitting in Florida traffic. Currently my coolant and oil temp run very close together at about 218 at the peak.

I found the temp switches that turns the fans on earlier in 180, 190, 195 and 200 degrees variants. Naturally I leaned towards the 180 but upon reading the description the 180 version says to use with "high modified cooling systems only" while the others say use with "stock cooling systems only" of which I have.

I'm confused. I know these engines are designed to run hot but maybe I'm just paranoid. Why isn't the 185 degree good for my stock engine.

Thanks as always for the education

Bob

 

The auxiliary fan will not really fix any overheating issue (actually your temps are fine), it just doesnt work as good as the main fan at moving air. The switches you see there are for the aux., not the main, which is ECM controlled.

You can use whichever one you want, mine is a 185. Just dont expect it to drastically lower your temps.

 

And chances are, with the lowest temp fan switches the fan will run excessively, maybe never turning off after coming on, wasting fan motor life and gasoline. Also, at speed, a running fan can actually impede airflow.

RACE ON!!!

 

Bob: Suggest you consider changing the t'stat from a 195 deg F to a 180 deg F. In addition, install a manual switch for the main fan. The only downside to this mod is that once you manually switch on the main fan......it stays on until you turn if off. The mod is easy and cheap.

 

I have a 88. I have one fan. I thought that the fan shut off at a certain speed. That's why I wasn't concerned about starting it at 175 degrees. Am I wrong about that? I just want to get the facts straight before I give any advice. And yes, I'll check the FSM when I get a chance.

 

218 is perfectly normal. You're radiator is doing all that and doesn't even have airflow across it, so rest assured, the radiator will have no problem cooling the car when the temp creeps up enough to trip the fans on. And putting a lower temp stat in will do absolutely nothing to reduce those peak temps.

 

218 = normal

 

The computer turns the fan off at 30-40 mph, exact number changed over the years. If the fan was running at highway speeds it would actually become a restriction to airflow.

Not sure what you mean on starting it at 175 degrees.

You want the fan shut off temp to be above your thermostat temp. I would say probably 10F higher than the rating, because they're never full open at the rated temp. This way you have some deadband. It is pointless for the temps to overlap, you could potentially have the fan running, cooling coolant that isn't even being circulated because the thermostat is closed. The fan ON temp should probably be about 15F higher than the off temp. If it's only say, 5 F higher, the fan would short cycle, it'd come on for 30 seconds then shut off. Then come on again right away. This can kill the fan motor because the motor coils heat up the most when it's first turning on, that's when it sees the most torque.

 

Thanks, Kevin. I had my chip burned by Ed Wright at Fastchip. I'm sure he did a good job. The chip is programmed to turn the fan on at 175 degrees. As you know I have a 160 thermostat. I will not recommend a 160, which seems to fit my needs. I will give a link. I think it's a good article, but I didn't write it. http://gmtips.com/3rd-degree/dox/tips/cool/cool.htm

 

The fan does not turn off at speed unless specifically programmed to do so. This seems to be universally misunderstood.

This can only be accomplished by the setting of greater AC off fan on/off temperatures compared to the AC on fan on/off temperature settings as the AC on settings are used exclusively below 11 mph. This also only works when the AC is off. Otherwise the AC on fan settings will be used independent of speed.

The 35 mph speed threshold only influences the duty cycle choice when the AC is on and the AC high pressure flag is set. It does not turn the fan off.

With factory tuning the fixed duty cycle and variable duty cycle table values are all set to 100% so there is no effect unless the programming has been modified.

 

Tequila, I understand but not completely..
Which constant(s)/table(s) I have to change in order to turn off both fans at 40 mph?
I changed the constants related to these speeds on both fans (I have 2 fans). I never knew that some interaction was present with the A/C (deleted on my car..)
-Beppe-

 

What year are you talking about specifically? I'll doublecheck the book when I get home. Although I expect even the descriptions there are oversimplified compared to what's actually on the chip.

 

That has never stopped you before. Get back to us AFTER you do.



The 160° stat fits your misinformed wants, not your needs. Even your own link, which I don't totally agree with, says, "There is evidence that the 160° stat is too cold for these engines".

RACE ON!!!

 

(assuming the AC is off)
The manuals say it shuts off at speed, but his data suggest otherwise.

So unless I actually see that mine does not shut off at speed, I'll have to continue to say that it does.

 

My comments apply to 86-89 L98s.

85, 90 and later may be different.

Beppe, sorry I don't have a 90 bin or disassembly on hand to provide specific instructions, but the same approach is likely to work.

Assuming the 90 follows the same design: (Wrong)

Raise the A/C off fan on/off settings relative to the A/C on fan on/off settings, even if your AC is gone, the AC settings will still be used below 11 mph. I would suggest you go about 20F greater than the A/C on settings to provide a reasonable window.

You may also want to shorten the fan minimum on time down from 15 seconds. This should have the effect of turning off the fan above 11 mph when the coolant temperature is below the A/C off fan off temperature after the delay time expires.

You could raise the 11 mph threshold to 40 mph if you want, but I think its better to turn the fan off much sooner. The delay time may also be tuned for the desired effect. Your car probably gets to 40 mph in 2 seconds.

Edit: For 90 disregard the above info since the design is completely different than previous years. For 90 there are fan specific enable mph thresholds of 35 and 50 mph that can be used for this purpose.

In my case, I have shortened the delay time down to 2 seconds, and reduced the 11 mph threshold down to 5 mph. Now my fan will turn off 2 seconds after exceeding 5 mph, when the coolant temp is below the AC off fan off temperature, instead of 15 seconds after exceeding 11 mph.

When the AC off fan on temperature is exceeded, the fan will turn back on independent of speed. As long a this is set fairly high relative to the T-stat, it should be unlikely for the fan to reactivate at speed.

When scanning: observe the fan duty cycle to verify the behavior.


Here's an example of how it looks in the disassembly:

;*************************************** ******
; >>> Cooling Fan Tables & Params <<<
;
;
; TYPE $32 ECM MY 87
;
; COOL CAL VAL'S = = (deg c + 40) * (256/192)
Page 30
ABTC_HAC.SRC
;*************************************** ******
LC2F6: FCB 35 ; Fan D.C. = LC2F9 if MPH < 35 & A/C Press Hi
LC2F7: FCB 11 ; 11 MPH, If LT THRESH MPH USE AC ON CALS
LC2F8: FCB 75 ; 15 Sec, Min Fan On Time, (sec * 5)
LC2F9: FCB 255 ; 99.6 DC, Fan D.C. If A/C Pres Hi & MPH < LC2F6
; A/C ON
; COOL FAN SETTINGS
; 107c/105c
; HYST PAIR
;
LC2FA: FCB 197 ; 107 Deg c, Fan ON if Cool >= THRESH & FAN OFF
LC2FB: FCB 193 ; 105 DEC c, FAN OFF if Cool >= THRESH & FAN on
; A/C OFF
; OOL FAN SETTINGS
; 07c/105c
; YST PAIR
;
LC2FC: FCB 197 ; Fan ON if Cool >= 107c, (226f), & A/C OFF
LC2FD: FCB 193 ; FAN OFF if Cool >= 105c (220.5f), A/C OFF
;---------------------------------------------
; Fan Duty Cycle
; D.C. vs Coolant Temp
; Tbl Val = %D.C. * (256/100)
;---------------------------------------------
ORG $92FE ; DC Deg C
;---------------------------------
LC2FE: FCB 255 ; 99.6 80
FCB 255 ; 99.6 92
FCB 255 ; 99.6 104
FCB 255 ; 99.6 116
FCB 255 ; 99.6 128
FCB 255 ; 99.6 140
LC304: FCB 255 ; 99.6 152
;---------------------------------------------


;*************************************** ******
; >>> Cooling Fan Tables & Params <<<
;
; COOL CAL VAL'S = = (deg c + 40) * (256/192)
;*************************************** ******
DF82: LDF82 LDAA L0065 ; Filtered MPH
DF84: BRSET L0037,#$40,LDF94
; ... else
DF88: CMPA LC2F6 ; 35 MPH, Fan D.C.=LC2F9 if
MPH LT THRESH & A/C Press Hi
DF8B: BCC LDF94 ; BR IF MPH GT THRESH
; ... else
DF8D: LDAA LC2F9 ; 99.6% FAN DC
DF90: BEQ LDFC0 ; BR IF Z
; ... else
DF92: BRA LDFB9
;
DF94: LDF94 LDX #$C2FC ; A/C OFF FAN PAIR (ON/OFF)
DF97: BRCLR L0037,#$80,LDFA0 ; BR IF b7,
; ... else
DF9B: CMPA LC2F7 ; 11 MPH, If LT THRESH MPH
USE AC ON CALS
DF9E: BHI LDFA3 ; BR IF Vss GT THRESH
; ... else
DFA0: LDFA0 LDX #$C2FA ; A/C ON FAN PAIR (ON/OFF)
DFA3: LDFA3 BRCLR L00F4,#$FF,LDFA8 ; BR IF NOT $FF
; ... else
DFA7: INX ; INCR INDEX TO FAN
OFF VALUE
DFA8: LDFA8 LDAA L005B ; COOLANT TEMP
DFAA: CMPA 0,X ; GET FAN ON/OFF THRESH
Page 153
ABTC_HAC.SRC
DFAC: BCS LDFC0 ; BR IF COOL LT THRESH
; ... else
;---------------------------------------------
; Fan Duty Cycle
; D.C. vs Coolant Temp
; Tbl Val = %D.C. * (256/100)
;---------------------------------------------
DFAE: LDAB #$A0
DFB0: LDX #$C2FE
DFB3: JSR LF337
DFB6: TSTA
DFB7: BEQ LDFC0
DFB9: LDFB9 LDAB LC2F8 ; 15 Sec, Min Fan On Time,
(sec * 5)
DFBC: STAB L00F5
DFBE: BRA LDFCD
DFC0: LDFC0 BRCLR L00F5,#$FF,LDFC9
DFC4: DEC L00F5
DFC7: BRA LDFCF
DFC9: LDFC9 CLRA
DFCA: BCLR L0034,#$08
DFCD: LDFCD STAA L00F4
DFCF: LDFCF RTS

 

Tequila, If I good understand your bold edit descriptions, my 90 will shut off the fans at 40 mph because the fact that the 90 has specific "enable mph thresholds" ??. (I changed these thresolds some time ago from 35 mph and 50 mph to both at 40 mph...).
-Beppe-