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Hot Rods wierd heat, electrical issue, need ideas

Discussion in 'The Hokey Ass Message Board' started by metalman, May 29, 2015.

  1. metalman
    Joined: Dec 30, 2006
    Posts: 3,280

    metalman
    Member

    Hey guys, got one we're having trouble figuring out, could use a few ideas to try. We have a 40 ford here in the shop, small block Chevy. Runs fine till it gets to 190 degrees then the motor dies but ONLY if the electric fan is running. Turn the fan off and it'll stay running till it get to 220 (haven't push the temp higher then that), Turn the fan on anytime it's 190 or higher and it's like a kill switch, motor dies instantly. Below 190 you can turn the fan on and off with no issues. Fan is wired direct thru a switch and relay, no termo switch. Got me puzzled, if it died always at 190 I'd say a coil or module, if it died anytime the fan was on I'd think the fan was drawing to many volts but I can.t correlate temp and electrical tied together causing an issue. Suggestions? I'm already bald enough, hate pulling more hair on this!
     
  2. Davyj
    Joined: Jul 11, 2011
    Posts: 442

    Davyj
    Member

    Try and run a hotwire direct from the positive battery post to the distributor and see if it will run with that, that will isolate whether the problem is the battery, or in the ignition wire circuit. If it stays running, then begin checking with a wire to the power wire to the ignition switch, and then at the other side of the switch. it has to be a draw from the fan circuit, the question is where does it affect the power to the distributor.
     
  3. Check your grounding, on both the fan and particularly the engine block. Temperature increases resistance, if a connection gets hot it's resistance will go up. If you have a connection that's marginal, the inrush current for the fan may be drawing the voltage down enough to reduce voltage below the amount the ignition needs to operate.
     
  4. Jalopy Joker
    Joined: Sep 3, 2006
    Posts: 26,663

    Jalopy Joker
    Member

    relay wired correct, in good condition?
     

  5. Wire high enough gauge? Try replacing the relay with a higher rated one if it is. Had a jeep once that did this. New relay (higher amperage one) cured it.
     
  6. metalman
    Joined: Dec 30, 2006
    Posts: 3,280

    metalman
    Member

    Davyj, I thought tomorrow I'd try running a hot directly to fan from the battery so it wasn't drawing thru the fuse box and the ignition circuit to see if that changes anything, it is currently wired into ignition hot so I know they are tied somewhere. That would serve the same purpose as hot wiring the distributor, separating the two circuits.
    Crazy, checked the grounds already, first thing we did.
    I'm still puzzled what water temp has to do with it, neither the fan nor ignition really has any connection with water temp. Engine compartment heat seems not to be a factor but it must.
     
  7. metalman
    Joined: Dec 30, 2006
    Posts: 3,280

    metalman
    Member

    Relay is new, rated at 30 amps. I'll bypass it as well tomorrow, when I wire the fan direct to battery.
     
  8. The 39 guy
    Joined: Nov 5, 2010
    Posts: 3,021

    The 39 guy
    Member

    You did not mention a fuse in this direct connection from fan to battery. It may be that it was too obvious ( to you) for you to not mention it...... But I thought I would throw it out anyway.
     
    Last edited: May 31, 2015
  9. GTS225
    Joined: Jul 2, 2006
    Posts: 1,188

    GTS225
    Member

    *******************************************************************************************

    This sentence throws a yellow flag and merits discussion.
    How large a wire is feeding the fuse box? (You might be getting voltage drop if it can't handle the load demand.)
    What type of ignition system?
    Seems to me that your common "interface" is that fuse box/panel. Might it be possible there's some bad work in it, internally?
    I'm leaning toward voltage drop effecting your ignition, especially if it's an electronic system.

    Roger
     
  10. metalman
    Joined: Dec 30, 2006
    Posts: 3,280

    metalman
    Member

    The wiring harness is a Rebel, I think the fuse box feed is 10 Ga. I too lean towards a voltage drop killing the ignition, it is electric. Only problem with that theory is it seems like the voltage drop would be present anytime the fan is on, I see no reason the fan would draw more current when the motor is hot.
    Geez, I hate electric fans, wish there was an easy way to put a mechanical fan on a 40.
     
  11. Won't help your electrical problem; but a mechanical fan fits on a sbc in a '40. 40.jpg
     
  12. GTS225
    Joined: Jul 2, 2006
    Posts: 1,188

    GTS225
    Member

    ***********************************************************************************************

    AH! I thought the fan was only coming on with a thermo switch at 190, and killing the motor. The fact that it runs fine until 190, even with the fan, does through a wrench into the works. More thought required. In the meantime, just for the helluvit, throw an additional 10 gauge wire on it, from the batt to the fuse panel feed terminal and give it a try It might give you some info the work with.

    Here's something else, and I may be grasping at straws; Is there a thermo switch anywhere in the entire harness? Might you have gotten a miswired harness, that happens to have the ignition hot running through that thermo switch?

    Roger
     
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  13. metalman
    Joined: Dec 30, 2006
    Posts: 3,280

    metalman
    Member

    I'll take straw grasping at this point but no thermo switch anywhere on the car.
    Today I rewired the fan to run off of a 10 gauge wire directly to the battery bypassing the fuse box (I did put a 30 amp inline fuse in) so the only thing tied into the ignition circuit is the power for the relay. Didn't help, 190 and motor died. Didn't have time to let it cool down today to try anything else, Monday I think I'll temporary bypass the relay just to be sure it's not the weak link.
    Questain since I don't deal with electric fans often. While I was warming up the motor I put a volt meter on the alternator, it was charging 13+ volts. Turn the fan on and it dropped to 11.9/ 12 volts. Is it normal for these fans to pull the power down that far, seemed excessive to me. I'm thinking maybe (a) the alternator is weak and can't keep up with the load or (b), the fan is defective and taking too much current to run. Still doesn't explain the temp issue thou.
     
  14. olscrounger
    Joined: Feb 23, 2008
    Posts: 4,244

    olscrounger
    ALLIANCE MEMBER

    alt voltage seems low--should be 14+
     
  15. trollst
    Joined: Jan 27, 2012
    Posts: 2,025

    trollst
    ALLIANCE MEMBER

    I wonder....seems you probably have a blown diode in the alternator, it should increase the voltage as needed, should run in the 14 volt range, at 12 volts it's not charging. I'm wondering if the fan draws too much when hot, causing the voltage to drop low enough the electronic ign cuts out.
     
  16. Is a 30amp relay big enough for the fan?
     
  17. We really need a bit more information.... First, do you have a watts/amp/HP rating on the fan motor? Some of these can draw more power than you might think. Motors (like cooling fans, heater/ac fans, door/seat motors) will generally be the largest single-point loads in any vehicle electrical system and all will have a large starting inrush current (300% or more of running current) that can easily overtax inadequate wiring. Second, what kind of ignition are you running? Points or electronic (what brand/style)? If electronic, does it have some sort of internal protection circuit? Keep in mind that almost all 'protection' circuits operate on generated heat (ambient and/or heat caused by an overcurrent). Third, you state that the motor 'shuts off anywhere above 190 degrees'. Now, you've already said it's manually controlled, so does the motor only shut off if you turn on the fan once the motor has reached 190, or does it also shut off if the fan is already on but kills the ignition once the motor reaches 190?

    Another issue with motors is they can have very different amps required depending on the conditions in which they're used; amp ratings don't tell the whole story. Motors are actually rated in horsepower, and that's a critical difference when figuring actual amps needed. Here's why....

    A motor is doing work, whether it's turning a fan, moving a window, or raising an antennae. You need X amount of HP to perform that work. But what happen if there's a drag or bind? Now you need more power to do this work... so what happens to motor amps? Horsepower is defined as 1 HP = 750 watts (rounded off). So let's say the motor is rated at 1/3 HP, but only 1/4 HP is needed to do the work. So the 'rated' current at the full 1/3 HP would be 20.8 amps (750/3 = 250 watts. Watts is volts times amps, so divide 250 by 12 volts). But if only 1/4 HP is needed, actual current will be only 15.6. But if a drag is present and the load needs 1/2 HP for the same 'work', now amps go up to 31.2. Don't know the HP? If you know the 'rated amps' or actual amps, simply multiply that by 12 to get watts/HP. I'll note here that if you do have an issue and the amps needed are more than expected, don't simply increase the circuit size; find out why it's higher. That motor can overheat and present a fire hazard.

    Another issue is voltage drop; as current goes up, voltage 'lost' in the circuit increases. Let's look at that 1/4 HP load again. At 12 volts, you need 15.6 amps to produce 1/4 HP. Drop the voltage to 11 volts, and now you're up to 17 amps. Drop another volt, and now it's 18.7.

    I suspect that voltage drop is playing a large part in this. I wouldn't be very surprised to find that the fan is drawing in excess of 25 running amps at 'normal' voltage, if you drop 1.5 volts current can climb to nearly 29 amps or more to do the same 'work'.


     
  18. GTS225
    Joined: Jul 2, 2006
    Posts: 1,188

    GTS225
    Member

    Might you have another electric fan laying around, even if it's a salvage yard piece? Swap the fans out with the same (troublesome) wiring scheme?

    Roger
     
  19. metalman
    Joined: Dec 30, 2006
    Posts: 3,280

    metalman
    Member

    OK, good, getting some good info, thanks guys!
    Crazy Steve,your info is good, here is the info your asking that I can answer. I have no idea of the rating on the fan. I can't even think of the brand right now but it's one our local speed shop sells, I and others have been using them with no issues before. Distributor is a Performance Products electronic from Speedway, the cheapest one they sell. I don't know anything about them other then some of my "price driven" customers have bought them, unrelated I know but one guy has 30,000+ miles on his without a hickup. Can't tell you if it has an internal protection circuit. As far as the temp thing goes, if I let the motor warm up with the fan on the motor will die once it hits around 190. If it warms up without the fan on it will climb to 220 and not die, I shut it down myself. Below 190 I can turn the fan on and off without issue, above 190 the motor will not run with the fan, period.
    I think the best info yet is the voltage drop increasing amps might be the key. My gut tells me the alternator is bad or the fan is bad drawing to much amps once everything warms up, or maybe a combination of both. I think tomorrow I'll try another alternator (the one on it now is one of those cheap generic chrome ones, I've have had lots of issues with them in the past), if that doesn't help I'll change out the fan. I'll change out the distributor as a last resort but I'm really not thinking it's the distributor.
    GTS225, I'm confidant it's not the wiring scheme on the fan causing an issue other the possibly a bad relay, I'll eliminate that possibility tomorrow as well. I'll keep you all posted what I find.
     
  20. rfraze
    Joined: May 23, 2012
    Posts: 2,003

    rfraze
    Member

    Is there a temp sender that is connected in some way to the relay or ignition (thru a ground circuit). Sounds like when the sender reaches 190, out go the lights. Try removing temp sender wire to test or replace sender with a different temp and see if it shuts off ign at that temp.
     
  21. Davyj
    Joined: Jul 11, 2011
    Posts: 442

    Davyj
    Member

    If you wish to fully check the distributor. Grab a spare fully charged battery. set it beside the car and run a ground to the intake and a wire from positive to the power side of the distributor. then fire up the car and let it run. if it shuts off , you will know that the temperature is affecting the module inside the distributor. Simple test to eliminate everything else. If it does not shut off, you then know that something is corrupting the power wire. something else must be attached to that power side of the key. Undo the wires one by one until the problem wire is identified.

    keep us posted, these problems are a great way to learn ............
     
  22. metalman
    Joined: Dec 30, 2006
    Posts: 3,280

    metalman
    Member

    Looks like it was a faulty alternator. Changed it out and it runs perfect (so far). Going to take the car to a cruise night tomorrow night, it will be a good test. Hope it works, the owner has had the car 17 years, this will be the first time he drives it farther then in and out of his garage.
    The voltage does drop as soon as the fan turns on but then is instantly jumps back up to 14 volts. Guess the old one was charging but not enough to keep up with the fan draw. Still don't know why it seemed related to water temp, I guess the warmer the alternator got the weaker it got. all I can figure.
    Sure would be nice if one could buy good parts, this make a new master cylinder and alternator on this car that failed before it even has 100 miles on it.
    Anyway, thanks for the help guys!
     

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