Are these readings OK?

Or am I headed for trouble?

Background: I just replaced an Optima Yellow Top (900CCA) with an Interstate battery (850CCA). I bought the Jeep several years back with an electric fan installed. The fan is on a thermostat, and it continues to run after the Jeep is shut off. The Optima was in the Jeep when I got it, so that's 2 years under my ownership--I have no idea how old it is. Over the last week or so, I was having sporadic trouble starting the Jeep and it would not start for sure when the fan was running. I had the battery tested at the parts store and it tested bad. So I figured the fan (and years in the desert heat) had finally worn the thing out. I got an Interstate at Costco, swapped it in and wired in a kill switch (just a toggle on the dash) for the fan. The switch is rated @ 35A and it's wired inline between the battery and the fan relay. There is an inline fuse near the relay.

Issue: On the way home from work today, I noticed my voltmeter (Sunpro), which always registered just above 14V, is now reading between 13-13.9V depending on engine RPMs. When I got home, I read the voltage across the battery terminals with a digital multimeter and recorded these readings: Engine off...13.08; Engine Running, Fan Off...14.14; Engine Running, Fan On...13.63. So, the voltmeter seems a little off compared to the multimeter, but why the difference in what the gauge reads between the 2 batteries, or is that to be expected? What I really need to know is if those numbers are good enough to ensure that my battery is being fully charged. Thanks...

 

is the engine running number as idle or accelerated rpm's?

 

Idle...around 700RPM...

 

My two electric fans are powered all the time. I haven't had any problems like you describe.

 

Power to the fan comes directly from the battery + post. I just checked the battery again, engine off...12.86, so it seems OK. I'm probably worrying over nothing, just kept envisioning being on the shoulder of the freeway in rush hour traffic.

 

The alternator regulated output should be read at about 1500 rpm under load (all power acc on) and it should maintain about 14.6 volt. If the voltage slowly drops off then the amp output of the alternator is inadequate for the full load. The 50CCA diff between the two batteries should not make that much diff.

 

Been working lots of overtime and haven't had a lot of time to tinker with the Jeep, but lately, on occasion, it won't start. When this happens, I turn the key, the voltmeter reads around 8, the alternator warning light is on and nothing happens when I try to crank it. If I just sit and wait a few minutes and try turning the key every once in a while, it will start (usually 3rd or 4th try with a minute in between). I just went out and checked the battery/alternator with the multimeter.

Battery read 12.74 with engine off.
Battery read 14.14 with engine on, idling.
Alt BATT post to neg post of battery read 14.24 with engine running.
Alt BATT post to neg post of battery read 14.10 with engine idling and fan on.(voltmeter did not match...read around 13)

So everything seems to be charging OK. I think I must have a bad connection somewhere in the ignition wiring. Last week I cleaned up all the grounds I could find...engine to firewall ground strap was connected to firewall with none of the paint scraped off...I ground it down to shiny metal and reattached. What is the most likely failure here? Ignition switch wiring? When I get the time, I will rewire entire ignition circuit...

 

When it failed to crank the engine over, could you hear the starter solenoid clicking?

 

No Walt, nothing at all.

 

Note the Delco solenoid on these starters are very voltage sensitive and you will note that the original wire from the switch to the solenoid is small (16?) gauge wire. Any loss of voltage along the way (phenolic/bakalite plug-in) connector at fire-wall in engine compartment is a known trouble area due heat/rust/corrosion and will cause the solenoid to not work. You may have a switch going bad as well. I ran an additional 12 gauge wire from the S terminal on the ignition switch to the S terminal on the solenoid for peace of mind. The S terminal on the solenoid is the small terminal closest to the engine block. This is if you have the delco and not the prestolite starter.

 

Thanks...I wondered about that size of that wire before, it is very small. I'll upgrade it when I get some time off. Appreciate it...