I recently replaced my the alternator in my 08 LR3 (V8) with a re-manufactured Denso unit (150 A) from RockAuto. When first installed, it cranked at 14.2V or so and held there during idle. Over the past week or so, i've noticed the voltage has begun to drop by one tenth of a volt every few days. So now, within the last 10 days or so, i've gone from roughly 14.2V at idle to about 13.6V. The battery measures full at rest (12.6V), and when cranked the voltage briefly hits 14.2V for a couple seconds then drops back down to 13.6V. Do I have a bad reman on my hands? Any idea what's going on here?

To be clear, im measuring these voltages at the battery. My GAP tool is showing slightly less, 13.5V or 13.4V, which is even more concerning (though likely not as accurate as my multimeter). The difference between no load and full load (all lights, AC, radio, etc..) is about a 0.2V to 0.3V drop, which appears normal.

 

Have you taken measurements at alt post to eliminate wiring issues? (Yes, i see it starts at 14.2 at batt but corrosion and heat can do odd things).

If you rev it up a bit or drive and then let it sit at idle a bit does it creep back up? The exciter on the alt could be different than your previous one. But this is typical of really old stuff and I wouldnt expect it on something like an lr3.

it is possible you have an alt not up to expectations and they can send you another one.

 

Definitely want to check the voltage at the alternator before going back to the seller about a faulty unit. Taking readings at the battery is not as accurate. The voltage you're getting at the battery is a concern, though. You could also do the AC check at the alternator with your fluke since you have one (should read zero or close to zero). Also worth checking all connections from the alternator through to the battery and terminals, etc whilst you're at it.

 

From the service manual section 414-02A Generator and Regulator:

The 'smart' regulator controls the output voltage from the generator to protect the battery; at low temperatures battery charge acceptance is very poor so the voltage needs to be high to maximise any re-chargeability, but at high temperatures the charge voltage must be restricted to prevent excessive gassing with consequent water loss. The EMS, which controls the regulator, will calculate the voltage set point required for the ensuing conditions. The 'traditional' regulator controls voltage against generator temperature, which means the battery temperature will lag a long way behind so there will be significant periods of operation when battery charging is compromised. information received from it's various sensors, hence voltage will follow the battery's needs a lot more accurately. With this system, the EMS can set the voltage by inferring the battery temperature from information received from it's various sensors, hence voltage will follow the battery's needs a lot more accurately.

Or something like that

Seems changing voltage is normal operations
Jeff

 

That is very interesting and I was actually hoping this would be the case. Funny enough, the voltage was back up to 14.2 - 13.9 today, but my battery voltage (when off) is slowly going lower and lower. In fact, its down to about 12.2V so ill be replacing that tomorrow.

Frustratingly, the electrical burning smell is back in the engine bay, though its very light. Im hoping this is just some residual oil burning off, but i've never experienced that before. Something still doesn't feel right, but will report back after I get the new battery in and re-check connections and the belt. In other news, while evaluating the engine bay, I noticed a coolant leak from the thermostat housing. I guess when it rains, it pours.

 

At least that's an easy enough fix. Replace the entire water outlet housing would be my recommendation. The top part of the thermostat unit (which comes as part of the thermostat housing) is cheaper and easier to do (and is I think available as a separate part), but if the plastic has become brittle you'll continue to see more leaks as it breaks down.

Did you check the voltage at the alternator?

 

If you can, put the battery on a charger. Do this before you go to bed for a few nights. If the voltage drops below 12.0 volts, then look at the battery, but give the new alternator and chance to get the battery back up to a good state of charge (thus the over night charger to help it along).

These things are electron hogs. If your commute is lass than 30 minutes each way to work, you are probably operating at a deficit. Remember the car take 15-20 minutes to completely shut down AFTER you pull the key out, and then every so often through the night it will turn on and check the status of things. That is the reason to pull fuse 26 when testing the air suspension as the car will self level over night. (lowering only).

Charge it up for a few days and let us know if it is holding voltage or if you had to replace it.

As for the thermostat? I agree with what pagodo said, change the whole "y" looking thing. The plastic gets old and can get hairline cracks, and besides, the complete unit has a new thermostat and temp sending unit.

Hope this helps

Jeff

 

....not only change it, but upgrade to a brass fitting.

 

Thanks for all the great responses.

I pulled the replacement alternator on the trail and replaced it with another Denso, but for whatever reason I kept getting the same issue. I checked the belts and literally everything I thought could be related. We finally got to camp and I began getting all sorts of error codes due to low voltage. My buddy charged me up for a bit and I got back to work trying to figure out what was happening.

As I sat there staring at the engine bay, I heard what I thought were relays. It turns out, the ground Post in my new AGM battery was making clicking sounds (arcing, I assume). I took the cable off and repositioned it, tightened it down, and it fixed the problem. I have no idea why this was an issue as it looked perfectly seated on the battery post.