I'm running dual spals on my car, about two years old. They have worked flawlessly right up til this past summer when I started seeing them not kick in when expected. I thought it was random, but now I see it's not. Grab a beer, this is one you won't wanna miss!

First, I thought maybe a bubble had been introduced into the cooling system and it was stuck behind the thermostat, which is right near where the Spal sensor is. (the recovery bottle was about a half quart low). I burped the system and it was good for a month. Or so I thought. I just wasn't driving it hard enough (you'll see what I mean below)

Next, when the problem recurred last month or so, I relocated the sensor to a place that I KNOW is fully engaged in coolant, no bubbles. I also burped it and drilled holes in the thermostat to allow constant flow like ya do when you first build a motor and need to run in the cam.

That lasted a while too, then I noticed that it would get hot only after I got on it HARD. Normal part-throttle, running it up to 3500+ between the gears and it's fine - you could drive it all night. But I'm noticing that now, for the past month I'm seeing that pattern. I can drive it easy, or fairly hard (just spirited driving) for a long time and it runs at 195* max. Usually 190*. But for when I decide to get on it. WOT thru the gears and spinning 5500 (max my cam produces power) makes the Spals not turn on, and then it starts running warm.

Last month, I was even beginning to think the 383+ Stroker had a seeping head gasket or something like that. But I'm seeing that pattern that I spk about above; it's not just that the engine is getting hot (210+) but the reason is that the fans stop coming on!! IT's WIERD, I tell ya!

Why would the fans work all day until I decide to run it through the gears? When this happens, the only way I can keep driving it is with the A/C on. The fans come on that way just fine. ... and that saves the day so I can get home.

The fans are wired with a schematic I got off this forum. Don't remember where I put it to tell you. There are three relays; one for each fan + one to turn them on for the A/C system. There's one single ground for the circuit, and one sensor. Both fans come on at the same time the way they are wired.

I have ruled out mechanical problems; the wiring is no where near the throttle linkage, and the relay connections are tight. Everything is clean and proper. The fans will cycle on and off for as long as I drive it normal or perhaps, part throttle to 3500+ or so. But as I said, the minute I get the space to really put it through it's paces, the fans stop coming on.

Suggestions appreciated! Go grab another beer and shoot me a suggestion. I'm going to grab one and wait...

OK I kinda lied. I just bought more than one but I'm still going to wait and hope somebody here has a suggestion..... I've worked on cars & hotrods all my adult life but this one has me stumped.

-Paul in San Diego

 

Any chance that you have a marginal wiring connection (possibly between the temp sensor and your SPAL control unit, or maybe even the ground wire)?

 

Sure ... but why would it work all day until I started really driving it HARD?

 

OK a few ???

This your typical driving habits? Any change in driving habits from past to now? If you drove easy all the time before you would not have noticed this!

What is your voltage reading when you drive "easy"?
What is your voltage reading when you drive "hard"?

Curious if your charging system has enough voltage to sustain spal fan operation at high RPM.

 

Very good Q.

My NORMAL driving habits with ALL my hotrods over the years, is to 'drive 'em like I stole 'em.'

With the Vette, it an auto so it's got a tall rear end. Can't really run it through the gears at 5K ++ unless I'm on the freeway. But yea this is my normal driving habit.

RE: Charging system voltage ... dunno. I do know that at idle, it charges at 13.8 - 14.0 V

I also know that the ammeter on the dash always indicates at least a small charge while I'm driving even when the fans are on.

When I get on it I always look at the oil pressure, and obviously the ammeter is right next to it and I think I'd notice if it was discharging.

But I do NOT have a voltmeter on the dash, just the factory ammeter. The only time it indicates a discharge is if the engine is off - or if the dual Spals come on at idle then it will swing to the Discharge Side for a second before that alternator recovers.

Also, remember that it is after the high RPM bursts, that it does not turn the fans on. Obviously the high RPM bursts are only seconds long, and I see the temp gauge climbing MINUTES later, when I realize the fans are not on. So the alternator is spinning at a normal RPM when the fans should be on.

 

just for info, where are the spal and temp gauge sensors located?

 

Any chance that your sensor is too slow to respond and this doesn't show up as a problem at normal engine operation? I seem to recall past threads indicating a problem with temp sensors supplied with spal fans. If I recall, there was a GM sensor that provided higher reliability. Maybe someone who experienced this will chime in.

If you are able to turn on AC to keep fans "on", and that controls temperature; the only other control is the temp sensor.

 

OK, I got 1 question. Do the fans come on everytime the sensor closes?
Stick a jumper on there to ground several times, see if the relays are picking up. You have seperate relays for each fan?

 

Yes, Yes, Yes. That always works.

 

The AC relay bypasses the temp control system. So it's just like grounding the temp sensor wire manually.

 

Temp Gauge is in the head; stock location. I have checked it numerous times to make sure it's accurate using a radar gun style temp reader. The temp at the top of the radiator & the thermostat neck is always within 5* of the actual stock gauge.

The sensor that is operating the Spal fans is in the intake. First, it was at the location of the OEM heater hose, which is at a 45* or so angle. When I moved it as per the second paragraph above, I put the sensor right next to the thermostat in a VERTICAL opening - and of course capped off the other with a plug. Previously it held the unused sensor for the heat riser valve (EFE Valve).

 

Does this mean you will be driving it easy on the Oct 13 run....???

Just kidding...
....seems you need to analylize what high rpms mean thru your alternator/fan circuit...one of your sensors could be on the fritz...

 

Just a thought but have you checked your belts? How old is the water pump? Sounds like you might be slipping a belt or the impeller inside the water pump since it only happens when you jump on it, i.e. crank up the rpms and put more torque on the belts and water pump. Since it only happens after you get on it, it's got be mechanical & not electrical. If it were electrical I would think it would do it all the time. Do ya have any coolant leaks? Like I said, just a thought.

 

could high rpm on the alternator cause a high output voltage that could cause the spal controller to lock up? do you have to turn electric power off to get the fans to resume normal operation?

 

Water pump & belts new when I built the motor - so they have 20K miles on them. Belt is tight by the rule of thumb I have always used: Taught in the middle, and you cannot turn the alternator pulley by hand.

This wouldn't explain the fans not coming on though. As you say, if it was electrical it should happen all the time, but if it was mechanical, though, I can't figure out how it stops the fans. I'm really perplexed.

 

Yea Rich I'll go slow so you can keep up! Hate to make your 502 stretch too hard to keep up with my mouse motor.

 

Make sure the fan negative power leads/black wires are grounded to the frame directly, I use the cross support with a star washer under the wire loop end, which is soldered to the wires, so not use the rad support, it's a bolt in, and as such can be floating...

I would also check that 3 relay thing you got there, also are these really SPAL speed controllers??? if so, they appear to be junk, just use straight relays....also the two primary fan power relays....check the contacts...shoud be good for 30 amps EACH....

also, you say the a/c controll over ride has another relay into the controll of the two main power relays??? if so, it would have to have a diode in there somewhere, seems a bit strange.....I would need to see a diagram of what you DO have to make further comments....

 

Ground is provided by a wire that is bolted directly to the intake manifold. Yes, the relays are indeed 30A units. I sure wish I could remember where I got the schematic (and what I did with it too) so that I could post it. I'll have to dismantle it and recreate the wiring diagram that way. Sure is frustrating that it's worked so well for at least a year & half now. This issue sure has beat me so far.

The wiring passes the wiggle test just fine; nothing is loose. I have rechecked all my solder connections and found no problems. I have tapped on the relays when the fans are not working, that has no effect.

Relay #3 just gets it's signal from the AC clutch wire, that's all. It's no different than the other two. The ground circuit speaks for itself. Power comes directly from the Alternator, which has been updated when I had it rebuilt to 105A. One wire each from relays 1 & 2 goes to the temp sensor; I have them soldered together and into a ring connector that's screwed tightly on to the sensor.

What I am unclear of is the wiring between the two relays. There's not much to it but I've created a wiring harness for it using 1/8" zip ties every two inches. So it will definitely take some more diagnosis time to dissassemble the harness and trace where I have the circuits going, if I cannot find the road map I followed when I created it to begin with.

 

Bad temp sensor is my bet.

 

I'd go with that too.

For those suggesting the "controller", he has indicated that the sytem used (3) three relays. One relay for each fan, and the third for the AC override.

The new temp switch is only about $25, but if you want to do a test, try this:

Add a wire onto the temp switch and run it into the car to a simple radio shack toggle switch. Out of the switch to a good ground. When the problem happens, flip the switch. If the problem goes away, the only thing you eliminted was the temp switch and that would mean it's acting up. I have seen the post on these switchs loosen up.