Coolant fan information please.

[Ronnie]

I have installed a 160 degree thermostat to keep the engine running nice and cool. To keep the car cool in traffic I intend to install a coolant fan control sensor kit. The kit comes with a probe that installs in the radiator fins, which activates a relay to turn on the coolant fan(s) at 185 and off at 170 degrees.

The relay may not be able to handle the amperage of both fans running at the same time. It will only handle 30-40 (not sure) amps. I have not checked to amperage of the fans yet.

If I am only able to control one fan with the relay, does anyone know which of the fans cools the best... the front pusher fan or the rear puller fan?

Any advice is appreciated.

[Roadster90]

Ronnie,

Write Padgett Peterson (Our "Padgett") a PM

This sounds interesting. My a/c in the summer in high heat at stop lights stops blowing cool (blows warm until moving again), and this may possibly do the same as having the prom re calibrated.

Nic

[Ronnie]

I have been kicking this idea around for some time. I don't like the thought of my engine going way above the boiling point when in traffic before the fan kicks on.

I originally wanted to use the fan relays that already control the fans but I found if you tap into the light green/black wire used by the ECU to control the fan relays the ECU will give a code E026 (the infamous quad driver code). If you disconnect the same wire from the relays and control them manually you get the same E026 code.

What I intend to do is control the fan(s) with an external relay (picked up by the temp sensor) wired to supply 12v power directly to the coolant fans. The way it will be wired will allow the ECU to still control the fans. The new relay will just run the fans at a lower temperature. If the new relay fails for some reason the ECU will still control the fans as normal. I have already tried this manually and it seems to work fine. now I need to add the coolant sensor kit to make it operate automatically.

I have the coolant temperature sensor kit ordered and should receive it in about a week. I will let you know how it turns out.

I do have one decision to make before installing the kit... whether to make the coolant fans run only when the ignition key is in the run position OR to make the new system independent and have the fans run anytime the temperature is high enough. That would mean the fans could run after you leave the car at night. Any thoughts on this? Anyone?

[KDirk]

Ronnie,

This sounds like a good plan to me, rather than modding the PROM to lower the fan activation temperature. Also, it provides a level redundancy as you pointed out. As far as allowing the fans to run on with key off, I don't see a problem with this as a lot of cars do this normally anyway.

That having been said, maybe some kind of time limiter (say 10 minutes, like retained accessory power) might not be a bad idea to prevent battery run-down. I know the car has an inadvertent power shut-off feature so if the door is left open for example, the interior lighting is automatically killed after about 10 minutes. At least that is the case on my 91.

This could be achieved with a pre-built timer circuit (somewhat complicated to implement), or even a time-delay relay wired ahead of the fan control relay. The latter could be purchased from an electronics supplier like Allied or Mouser as long as there is a 12 volt DC version.

Just my thoughts.

KDirk

[Barney Eaton]

Ronnie and Kevin.... if you don't have a service manual, you really need one.

In the manual, you will find the fans are controlled by the ECM. Under normal conditions, only one fan is on. When you turn on the A/C both fans are running but in series meaning they are running at 1/2 speed. Only when the temp sensor reaches the factory predetermined (panic) point, do the relays get picked to give each fan 12V.

Padgett did a eprom for me and lowered the panic point and I am very happy with the results. My temp would creep up to 1, 2 and sometimes 3 ticks past 12 o'clock with the stock setting. This only happened in traffic but it was desturbing. Since the change, I have never seen the gage go past 12 o'clock.

[Reatta45]

Ronnie… I trust you are aware that the system places the fans in series for low speed operation and parallel for high speed. You will need to be aware of this when you place 12 volts on the wiring. KennyV

[Ronnie]

Barney and KennyV:

You are probably correct on some models. My fan is wired as shown in the photo below. I have a resistor as shown in the photo for the low speed operation of the rear (puller) fan that is operated by a seperate relay. Fans are not hooked in a series for slow speed. See Reatta.net FSM 6E3-A-5.

I intend to use circuit 533 to power the fans.

[Reatta45]

Ronnie.

At will work. My 91 uses the series low speed system.

You could use a DPST relay and catch both fans the way yours is wired.. KennyV

[DAVES89]

Ronnie,

Where are you getting yours and what is the brand? I found one at AutoZone and then there is one by Mr. Gasket.

[Ronnie]

Dave, does your '89 have the same fan wiring as my '88 or do you have the fans that are in a series as described by Barney and Kenny?

I ordered a Hayden #3652 (non-adjustable - on at 185 degrees and off at 170 degrees) from Advance Auto Parts. $26.99 plus tax. It seemed to be the most simple of all the ones I looked at.

I was told by the salesman if it doesn't work as expected or I don't like it I can return it and get a full refund. OR if I want the adjustable one (#3647 $36.99) I can return it and pay the difference to get it.

[DAVES89]

I havn't looked yet. I am still in the information gathering stage. I will compare my FSM with the FSM that you printed this week.

[Barney Eaton]

I just compared the 1988 and 1989 and they are different.

The '89 and later cars do not use the resistor that is in the Puller (rear) fan and because of that are wired differently.

[D-a-n-i-e-l]

I agree running a engine at a lower temp is a way to produce more power and run more effeciantly, and I do run mine at 180.

Do however keep in mind that running cooler can cause other issues. First, if you have to deal with emissions a lower operating temp means less burn and breakdown of the gasses that will fail your test. Second, the cooler temp means more build up on exhaust vaulve and other exhaust parts.

Also the boiling point you are talking about is the boiling point of water at sea level and atmospheric pressure. The fluid in your engine is upder pressure and not all water, so its boiling point is a bit higher

Just two sense but I do like where you are going with this.

[Guest simplyconnected]

Looking at the circuit, FRONT FAN and REAR HIGH always come on together.

I understand, this happens in A/C or DEFROST modes as well.

I'm concerned about running your engine with a cold thermostat. When your engine block runs hot, two things happen. Fuel economy peaks, and engine wear (friction) is minimum. Your engine will last longer.

Fans do their best when there is a greater temperature differential between ambient and coolant temps. Sometimes they do too good. (Truckers cover radiators in winter.) If you put a lower thermostat in, that won't affect cooling efficiency. Your engine creates heat depending on the load over time. Your cooling system must be sized to handle that.

If your OEM system isn't responsive enough, the new thermostat and relay make solid sense. Sensing at the radiator is a great idea. As far as where to tie-in electrically, once your radiator comes down to 170, it will shut off by itself (whether you're there or not). I doubt if it will take even five minutes. Because you are tieing into 533 (HS Rear Fan), your added relay contacts only service one fan (unless both 533's are tied together). I just noticed both fan wires are 533 and not tied together.

Dave

[KDirk]

Barney and all,

just a disclaimer, I was commenting on what Ronnie was wanting to do only to the extent of making a design change based on what he had described in his previous post. I was not basing my remarks on the particulars of the stock operation of the dual speed fans. Nor was I taking into account the differing circuit setups, of which I was unaware until I read it here.

FWIW, I trust GM's engineering and would not likely make such a change on my car simply because I don't see the need. I respect others choice to make changes they deem necessary and try to provide useful input to that end if I have something worthwhile to add.

Anyway, if what I said is considered bad advice, my most sincere apologies. I do have a service manual (3 actually, 1 1990 an 2 1991) and always consult it if I am doing anything major or unusual to my car. Likewise, if the discussion were specifically about the way the fans were wired or how and when they ran, I would have gone to the FSM for the answers.

Just wanted to clarify in case anyone thought I was blowin' smoke.

KDirk

[Ronnie]

Barney, I do have a service manual both paper and electronic. Thanks for verify what I said was true.

Thanks to everyone for your comments on this subject. I would point out that I have not recommended or suggested that anyone should do this modification so anyone who offered encouragement to me need not apologize or add a disclaimer for doing so.

I find it amusing that after 13 additional posts I have not got an answer to the only question in my original post.

I wrote:<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">If I am only able to control one fan with the relay, does anyone know which of the fans cools the best... the front pusher fan or the rear puller fan?</div></div>

[Reatta45]

Ha … you are right. Had not even noticed it was not addressed.

The answer is the pull fan the one in the rear. That is why the factory turns it on first. That is also why you always try to mount a puller fan inside, when there is room, when you are cooling an engine in a hotrod… KennyV.

[D-a-n-i-e-l]

I agree with 45, the rear fan is the best for a single fan. You could always run a second relay and power both.

[jonlabree]

The simple way would be to modify the chip to have the fans come on at lower temps.

[Guest Greg Ross]

What's the root problem, are you overheating/ when?

May want to consider flushing the cooling system, radiator core could be toast, replacement of the rad. is obviously a last resort.

[Ronnie]

I have no overheating problems. I had a 180° thermostat installed last Summer and it ran 188° at highway speeds but sitting in traffic and not moving the engine temperature would go to 233° before both fans started running high speed and cooled the engine down. I personally don't want my engine to get that hot in traffic. It pushes hoses, seals and gaskets to their limits for no reason other than emissions. I would like to do my part in keeping the air we breath clean but I think I can find a better way to do it than melting down my engine.

I installed a 160° thermostat just to see if the engine would cool down further to let me know how well my cooling system is working. It now runs at 163° on the highway. (I'm sure this varies a few degrees with each individual thermostat and outside air temperature.) I hardly ever drive my Reatta in the cold months so I may leave it in.

I keep hearing that the simple way to change the point where the the fan come on is to modify the chip. That would be simple for someone who owns the software and hardware that is required to reprogram the chip. Of all the threads on this forum where I see someone say how simple it is to modify the chip have I never seen anyone offer to do a chip modification for anyone. I have seen where it was suggested that GMtuners could do the job.

I will get it done the hard way and if I'm not satisfied I can undo it simply removing what hardware I have installed and be right back to the factory setup. Other than tapping into circuit 533 that powers the fans I will not be modifying any stock components.

[KDirk]

Ronnie,

Regarding the chip, if anyone here has a ROM image they can send me of a modded PCM PROM that is known good, and has the lower fan activation point, I could burn the chip for you. I do have a programmer, and AFAIK, the chip is just a 27C128 or 27C256 type PROM. Or, if anyone can send me an un-modified ROM image that matches your model year and tell me which bytes to change and what values to put there, I could do it that way also.

I don't have a UV eraser presently (have been working with EEPROMS, not UV EPROMS, so no need for it) but you could always just buy a "blank" chip new, and burn it. That way you keep the existing one as a fallback.

KDirk

[Ronnie]

Thanks for offering your help Kevin. I really appreciate it. I may need to go that route if I fail in what I'm trying to accomplish.

I would also like to raise the speed at which my torque converter locks up. Right now it locks at about 47 miles per hour. I would like to delay it until about 52 mph. That is something I have not found a way to do with relays yet.

With all due respect to everyone... is it really simpler to modify the chip than add a sensor and relay? What you said may in fact be simple but it sure sounds complicated to an old mechanic like me.

Thanks to everyone who has commented about the cooling fans.

[jonlabree]

Yes it is and Ryan at GM tuners can modify for you.

He can also change the lock-up speed at the same time.

[Guest Greg Ross]

ECM PROM tuning is the way to go, clean and simple in the right hands!

First mods done on mine prior to manual Tranny and S/C was to push out the Lock-up and also alter the % TPS shift points.

I got educated on what parameters the ECM PROM responded to as far as shift points were concerned. Gave a noticeable improvement IMHO.

[Ronnie]

<span style="font-weight: bold">This coolant fan modification may only work on the '88 models. Other models may be wired differently.</span>

For anyone interested, I installed the Hayden fan control relay kit (#3652) today. Everything went as expected. All wire connections were made underneath the fuse/relay block under the hood and the relay fit inside the fuse/relay box. However I did run into a problem. The probe that is inserted into the radiator would not sense the temperature properly. The fan would not come on until the temperature was past 210°. That was too high.

To correct the problem I drilled and tapped, (6-32 tap), the center of the bolt that holds the thermostat housing in place and screwed the thermal snap switch, that came with the kit, into the head of the bolt. Now the fans turn on at 191° and turn off at 176°.

I'm happy with the outcome but looking back I would spend the extra $10.00 to purchase the adjustable model of the fan control relay. That might allow the probe to work in the radiator as intended.

Probably the better way to go is to get someone to modify the PROM if you can get someone to do it. Sometimes there is a little satisfaction to know you did it yourself the hard way.