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Discussion Starter #1
Hi everyone!

My car is a '68 Mercury Park Lane with a 390. I'm running a Holley 1850 4 barrel, and the stock points-based ignition.

It runs hot all the time. This I've deduced from the dash light. "HOT" it tells me. Pretty much all the time. I've got gauges on order so that I can figure out HOW hot, but the plugs are white, so I think it's safe to say that we're too hot. The cooling system is full with 50/50 water antifreeze mix.

I've read in various places that the voltage at the coil should be 9 volts, and is stepped down by some kind of resistor? I'm running 12 volts, as measured at the positive pole of the coil.

Could that be why I'm running too hot? Is it possible that the resistor unit is still in the car, just wired out of the system by a PO? What do I look for?

Any insight is appreciated.

68M
 

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Hi everyone!

My car is a '68 Mercury Park Lane with a 390. I'm running a Holley 1850 4 barrel, and the stock points-based ignition.
HI. :)
It runs hot all the time. This I've deduced from the dash light. "HOT" it tells me. Pretty much all the time. I've got gauges on order so that I can figure out HOW hot, but the plugs are white, so I think it's safe to say that we're too hot. The cooling system is full with 50/50 water antifreeze mix.
DO pray-tell HOW just those gauges are reading. Nothing but information that we need in order to better assist you.
I've read in various places that the voltage at the coil should be 9 volts, and is stepped down by some kind of resistor? I'm running 12 volts, as measured at the positive pole of the coil.
Voltage to the coil is stepped by a resistor wire in the loom and behind the dash. If you have NOT screwed with it then you have nothing to worry about.
Could that be why I'm running too hot?
Oh hell no that's got nothing to do with running hot.
Is it possible that the resistor unit is still in the car, just wired out of the system by a PO? What do I look for?
You look for a red wire with black stripe coming out of the harness connecting to the Coil +, then, under the dash just off the Ignition switch, look for a Pink wire pigtailed into the ignition a couple inches out of the switch it's self. That is the resistor wire.
Any insight is appreciated.

68M
That's my insight, but if you put the temps out here and a picture of this WHITE spark plug, you do know they're supposed to be white right, then we can start helping you....
 

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Have you changed the sensor? If its hot all the time even when it should be cold.
 

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... It runs hot all the time.
Welcome to FM. Get those gauges to verify it's actually hot before assuming anything. Historically, the #1 cause for 'overheating' is a bad gauge or light at normal temps. ;)
... the plugs are white ...
You're definitely lean at some point in your tune. That tends to cause hotter running, but would not be the root cause - if it really is hot.
I'm running 12 volts, as measured at the positive pole of the coil.
The voltage should be measured while the engine is running, as the ~9V is an average at the coil (+) terminal. Engine off, the voltage will follow battery voltage with points open, and ~5-7V with points closed. The resistance of the PINK wire under the dash does this, and should be there and functioning for a points ignition. If bypassed, it will still run fine at full battery voltage, but with engine off and key ON, the coil will fry fairly quickly if the points happen to be closed. The resistor prevents this. And, no - the coil voltage would not affect your engine temp at all. Let's see what the new temp gauge says (and when it says it) before we start making possibly misleading assumptions.

David
 

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Discussion Starter #5
Thanks to everyone for the quick replies. Indeed, I'm looking forward to getting my gauges, and I think I'll also invest in an IR thermometer.

The hot light comes on at the point that I expect the engine would be warm (idle 2 or 3 mins), and goes off when the car speeds up and air cools the motor. I'm convinced that it is sensing heat, but I don't know temps. You're all right, it's better to know than figure.

I'll do a plug chop as soon as I'm able and post some pictures.
 

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Discussion Starter #7
Okay. I fixed it.
Turns out that 1 of the 2 passages for the accelerator pump was clogged, and causing a lean condition. After cleaning it out, the hot light is no longer coming on. I'm still going to install the gauges when they come.

In any case, I'm still worried about running 12 volts to the coil. I couldn't find that pink wire under the dash... Should I install a ballast resistor? If so, where?
 

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I think the temp light comes on at around 240. If the temp light ever comes on it is a problem.

Accelerator pump only functions when you hit the gas to cover up the temporary lean spot by the throttles opening. They don't affect anything at any other time.

Back when you said your plugs were white I would have said that your carb idles or jetting is way too lean. I just read this thread. The engine running hot is a symptom of too lean carb which leaves the plugs white. It is not the other way around.
 

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Discussion Starter #10


Oh, Kay.
There's a curious (pink?) wire running from what I believe to be the heat sensor on the block to nowhere. It's birdsnested off right above the starter solenoid on the fender. Is this my resister wire? A lead to the ballast? Can anyone make sense of this for me?
Thanks in advance.
 

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You are going to have to get your wiring diagrams. Here is one that may or may not help much. I can't identify that square plastic box bolted to your intake. It looks to be a relay that was added. I don't think that would have been original but I could be wrong.

 

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Discussion Starter #12
FE&GB, I am getting 12 volts on the + side of the coil. The coil even says "use w/ external resistor". I'm totally going to install a ballast resistor as soon as I can figure out where to put it, how to wire it, and whether or not I've got one in there already that's just been wired out.

Hottaroad, thanks for your comments. For whatever reason, the hot light doesn't come on anymore. I'm not entirely convinced that the carb is running right (and I think I'll start another thread for that very soon here), but I want to make sure that my ignition is doing what it's supposed to here.

68m
 

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The temperature sensor for the idiot lights (hot and cold on a '67) goes into the water jacket on the intake behind the thermostat housing. I have no idea what that thing attached to the intake bolt in the last picture is, but if that is measuring the temp for the gauges then that could be causing the issue. No way it should light the hot light in 2-3 mins.
 

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Do make sure that your temp light comes on with key on before you start up. If not the bulb is probably burned out so it could still be running hot.

If you can verify that somebody removed the pink resistance wire from your ignition switch you can put the ballast resistor anywhere that is convenient to the wiring along the path of the + wire to the coil.

Somebody drew this up which looks pretty good.
Code:
 

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The temperature sensor for the idiot lights (hot and cold on a '67) goes into the water jacket on the intake behind the thermostat housing. I have no idea what that thing attached to the intake bolt in the last picture is, but if that is measuring the temp for the gauges then that could be causing the issue. No way it should light the hot light in 2-3 mins.
I had a little block , like the one in the picture bolted to the intake. In my case it was a temp sensor for an electric choke conversion I installed on my original carb.
 

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Oh, Kay.
There's a curious (pink?) wire running from what I believe to be the heat sensor on the block to nowhere. It's birdsnested off right above the starter solenoid on the fender. Is this my resister wire? A lead to the ballast? Can anyone make sense of this for me?
Thanks in advance.
You sir have NO pink wire in the photographs! At least you have no Factory pink wires.
Now let me settle a score here.

The FACTORY never let the Pink wire be VISIBLE in the engine bay, it's spliced in just after or right before or right AT the plug at the firewall.

That relay bolted to your intake is NOT OEM equpiment.
 

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Discussion Starter #18
OMG OMG OMG OMG!!!!!!


If you have a PERTRONIX unit in your Dist then you will have a red (could be mistaken for pink, and looking like the wire in your pic) wire going to the coil +


Just to let you know.
Upon further review, that block bolted to the block is mostly hooked up to the electric choke so; yeah. That's what that is.

Petronix? I don't think so. That's an aftermarket electronic ignition, right? I'm running a points ignition that I gather is stock...
 

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Discussion Starter #20
Hi, again, guys!
Pulled the car out because it's sunny in Vancouver, and I'm having the hot-light problem again. I've gone to install the gauges, but can't quit figure out where I'm supposed to put the sensor for the water temp gauge? Does it bolt into the thermostat?

Here's the plugs...



Too white, right? Or just about right?

I figure I'm supposed to put this sensor... I actually have no idea. It's one of those triple-gauge deals: water temp, oil pressure, battery amperage.

Any guidance?
 
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