OK, so I've been able to drive my truck enough(!!) that I've discovered a small problem... Basically, I can get it started easily enough (depending on how long it's sat, but the battery always seems strong) and drive it a bit with no problems (say 5 miles or so), then if I shut it down and try to restart it the battery acts like it's almost dead (barely turns the engine, won't start).

Let's see... the wiring was replaced about 1.5 years ago and a new battery put in at the same time along with wiring harness etc. for turn signals. It's a 6 volt negative ground system with a 6 volt alternator on it which is about 4 years old. The company I bought the alternator from suggested touching a screwdriver to the back of it to check for magnetism, which it has (when the engine is running). Beyond that, I've tried detaching/reattaching a few things (horn, turn signals, heater) to see if it's a ground problem, with no luck.

If at this point it sounds like I'm reaching blindly, yeah, I'm getting out of what little expertise I have. At this point I think it may be 1 (or more) of 3 things -- bad ground/connections, alternator not quite working, or starter problem. The alternator guy suggested the battery might be the problem, but I'm stubborn and can't see how that would be the case...

Tomorrow, I hope to fiddle around with my voltmeter and do some before/after testing of the battery. Any other suggestions?

 

Hi Jeff,

A couple of things to check.

You have to have a circuit with enough current carrying ability to handle the high current draw in a 6V starter. Start at one battery terminal and trace through the circuit for the starter. Check every connection for corrosion or loose fittings. For your 6V negative ground, the circuit should go something like this:

1. Battery minus terminal to a frame or engine ground
2. Engine block to starter case ground through the starter mounting flange and bolts
3. Through the starter windings
4. Out the starter terminal and to the starter solenoid
5. Across the solenoid main contact to the other solenoid terminal
6. From the second soleniod terminal to the battery plus terminal

You might have a ground to the frame and then another one to the engine. In either case, make sure the cables are in good condition and the terminals and fasteners are all clean and tight. Make sure the starter mounting flange is clean and the mounting bolts are clean and tight. Any of these things can degrade as the engine compartment heats up. It might start when cold and then lose the current carrying capacity in the circuit as the connections and wiring heat up.

You also have to have a battery that maintains its output as it warms up. I've seen a battery with one cell shorted internally. That leaves you with only 4 volts for cranking. I suppose it's possible for the battery to lose a cell as it heats up.

Finally, you have to have a starter motor that maintains it's ability to provide torque when it heats up. Bad internal contacts or a marginal winding could cause you problems when hot but not when cold.

Good luck and let us know how it works out.

 

High starter current draw after engine warm-up is very common. If all the connections are clean and tight as George mentioned, I'd have the battery load tested. Then check the charging output. I bet you are looking at a bad starter if those check out OK.

 

Jeff
Had a starting problem with my 97 Explorer, went to Auto Zone, they wheeled out a machine and did a complete diagnostic check, free, found a bad ground and a bad battery (Both verified).

 

Dewayne has a good point on the heat up. We have all heard the big block Ch**y trying to start after driving some distance. As a matter of physics, the more heat you have in a circuit, the more resistance, the harder to push voltage through the wiring and you get reduced curent , causing the starter to turn more slowly if at all.

HAve the grounds and wiring checked as George says, then think about some type of heat shielding in the starter area or probably better in the long run --consider going to 12 volt.

Happy cruising

Hands

 

Thanks for the tips, hopefully I can get out tomorrow and poke around a bit...

 

the 6v system has to push a lot of amps with low voltage. to do this you need vary large battery and starter cables. 2/0 (about the size of your thumb) is the correct size. also check if ALL the cables in the starter circuit are the same size. if not the smallest cable will heat up very quickly causing an amperage drop.

 

Okay, I had a little success yesterday. Checked all the connections and found two a little loose -- the wire connection to the starter and the starter mount to the engine block. Drove a bit after tightening everything and it still cranked real slow afterwards but did start up. Sort of a "rowr, rowr, rowr, rowrrowrwrowrvroom" (ooh, what sound effects!) So that's encouraging. The two wires from the battery are 5-6 years old now, but the one from the solenoid to the starter is, er, much older so I'll go ahead and replace it. The solenoid is maybe 4 years old. My neighbor thinks the nearby parts store can test it for me, and I can take the battery for testing at the same time. I'll let everyone know what happens...

 

First the good news -

Cleaning the wire ends and connect spots did the trick -- the Tank starts like a champ now, cold or hot. I hardly have to push the starter button, I think a hard glare might even work...

Now the bad news -

Went out for a lil' drive today and the sob was pegging the temp gauge. Actually, the whole story is I drove the Tank to a gas station (first time I've been brave enough to do that), then went for a ride. Needle slowly went up to and settled at midpoint, where it stayed for 15 minutes or so. Then up to 3/4 for a couple of minutes, then down an eighth for a few minutes, then slowly to the right end of the temp gauge. So I pull into a parking lot, can't see anything obvious and just wait about 20 minutes or so for it to cool down a bit, then creep home.

It was 95 today, which I'm sure didn't help any. I had checked the fluid level in the radiator a few days ago when I was playing with the starter wires, so I hope the problem is just that I didn't get the cap on tight enough. We'll find out in a few days...

 

jeffh

sounds like your thermostats are not working right. my 49 is doing the same thing, but it does not seem to be overheating. i am going to get a thermometer and check the temp. to see if the gauge is off. the rad. caps on these old trucks may look ok but do not hold the right pressure any more. you should be ably to get the cap and thermostats at napa for less then $15.

let me know how it turns out