Another check for Hot Start problems

[Paul Reynolds]

I have another thing for y'all to check when having hot start problems.

I've been battling this for a couple of months now. Rebuilt the carb, changed the coil, etc..... Today I think I found it.

As you know, a stock C2 ignition system uses a ballast resistor to lower the voltage (about 8V) to the coil in normal running conditions. When starting, there is 12V supplied to the coil from a terminal on the starter solenoid.

Here's what I found... Running, I have about 8V at the + terminal of the coil. When starting, I have 4V. I checked the 12V coming from the starter (during start) and it was 0V. All the wires in the harness checked good, so it's got to be the starter solenoid.

I took a cruise for about 1/2 hour, then sat for 15 min. As usual, it wouldn't start. I jumpered across the ballast resistor to give the coil full 12 volts, and the car started right up. Turned it off, pulled the jumper and tried again... no start. Put the jumper back on, started right up. Looks like I need a new solenoid.

During cold start, it appears there's enough voltage through the ballast resistor to the coil to fire a cold fuel mixture.

So, there's another check to make if you are having a similar problem.

[Gerard F.]

Re: Another check for Hot Start problems

Paul,

I'm having similar problems with a newly rebuilt 3810 on a 67/327/300. Thought I found it yesterday but maybe not. The problem is that it gets very hot after a long run, at idle. Runs real good at high speed and just cruising, goes up to 190-195 uphill with the A/C on but trims off to 180 downhill just doing 55. Then when I slow or stand at idle the temp goes up to 210. This never happened with the double-pumper I took off. The outside temp is about 100 these days.

Thought I found it yesterday when I checked the battery. Seems I cooked it, had to add about a pint of distilled water. Then charged it for about 8 hours.
Thought I solved the problem as today, it idled pretty good (I also tightened all the belts), but after a long run, the same thing. Maybe I really cooked the battery.

Still scratching my head!

Jerry Fuccillo
#42179

[G B.]

8 volts is low

You might want to change your ballast resister too. With your alternator charging at 13 volts, you should have about 10 volts at the coil.

[Paul Reynolds]

Re: Another check for Hot Start problems

Check the archives for "overheating". You will find a number of troubleshooting tips. I went through them all and for the symptoms you describe, it ended up being a number of items. Yours sounds like one of, or a combination of, timing, fan clutch, and/or radiator.

On mine, the timing map was good. The car would run hot at highway speeds. The radiator was an original, so I replaced it. It fixed the hot highway problem, but still had a bit of heating in slow traffic/idling. New fan clutch fixed that.

Everything has to work together and correctly for the cooling system to work properly. There's not a lot of room for deviation. I don't subscribe to "modifying" things to make them work. I put it together the way GM designed it and everything works well.

[Paul Reynolds]

Re: 8 volts is low

Thanks Jerry. That was the nominal voltage at low idle. At higher speeds it runs a little higher (9-10V) The ballast was replaced with a correct one last month when my aftermarket replacement went south.

A quick check to see if the starter is giving 12V at startup is to remove the wire going to the coil from the ballast resistor and try to start the car while measuring the voltage at the coil + terminal. If the car starts, there is voltage coming from the starter. The engine should stop when you release the key. Of course, this didn't work in my case since I have nothing coming from the starter solenoid.

[Gerard F.]

Fan Clutch

Paul,

Is there a test for the fan clutch? Mine seems to be turning at all speeds, perhaps maybe not enough at idle.

Jerry

[Paul Reynolds]

Re: Fan Clutch

Jerry, here are the "quick" checks.

With the engine off, see if there is any side to side movement of the fan in relation to the waterpump. Should be none.

With the engine cold, start the car and get it running at normal idle speed. Turn off the engine. Watch the fan as you do this. Fan should continue to spin about 5 revolutions after the engine stops.

Start the engine again, drive around and get it up to full temp or above (180* +). Maybe as high as 210. Open the hood. Turn off the engine. The fan should rotate no more than 2 revolutions after the engine stops.