Remove all the engine belts and see what happens. I've seen bad alternators cause this problem many times.

Thanks for all the ideas.

I had time to check the car today. First thing I did was spin starter without first allowing glow plugs to work. It spun over just fine. Then started car in normal way, again no problem.

I think I will wait until symptoms show up again and then do some checks. IOW, if it ain't broke don't fix it.

May be back later

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Well, it is a year later and I have same symptoms again. Just drove car. It initially started, but didn't spin freely. Drove about 20 miles to pick up some propane. When I got back in car, it barely turned over. Luckily it is very easy starting, so it fired and ran. Didn't think it would. Drove back home. Checked voltage and it was at 12.7 right after pulling in. Connected load tester - It showed battery in green (good condition).

So I guess, I go back to post #1 and start again

Job#1 is to check and clean battery/starter terminals.

Job #2 is to measure starter current draw. I have clip on DC meter, but don't know what current should be.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Did you check the voltage of the battery as the car was idling? If so that is to low, something is draining the battery and/or the alternator can't charge the battery...

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Yes and not only check the battery with the meter set on dc, but also take an ac reading.

You should have less than a couple hundred mV ac. (2-tenths of a volt for you non EEs)

If your ac measurement is above this, you have a bad diode(s) in your alternator. This seriously reduces the energy output of the alternator and actually can discharge the battery.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

I didn't check it while idling, but just did! (It reads 13.35V). I also checked DC amps at idle and they were in the 10-7A range and dropping (after car had been started a couple of times.

Some other things I have checked:
- battery voltage after car had been sitting for a while. 12.45V
- current draw with glow plugs and starter active ~35-40A
- current draw glow plugs only ~8.5-10A
- current draw starter only, after glow stops - ~24-25A

These mostly measured with Stop button levered to STOP position.

Meter is a clamp type that can measure both AC and DC. Measured on ground cable from battery. Reasonably warm day.

Starter current draw seems low, but I double checked that several times on both positive and negative battery leads. Motor was spinning freely, so may explain low draw. I think I recall this being a 2.3KW starter. So max current would be about 200A. Maybe in winter!

As happened last time around, the engine is spinning fine again! Makes troubleshooting difficult.

Have Hagerty Classic Car insurance. Thinking of adding their Roadside Assistance, just in case! Then have to remember to take my cell phone with me when driving

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I would remove the negative cable from the battery(car off of course) and check with a check light and see if you have any current draw(i've used a rear dome light) If the bulb lights with the car off and all doors shut you have something drawing current from the battery when the car is off. If it doesn't glow, I would pull the alternator and stator....have them tested....

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The amp numbers are not credible, they are too low. If the engine was cranking at normal speed, your clamp amp meter is wrong. You have a load tester? If you know the specs on it, use it to check your amp clamp meter.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I hate working on washing machines and dryers & usually give them a quick test per professor Google then throw them away and buy another. They are little money for trouble free operation that working on them isn't worth my time.

Mechanics on the other hand charge $75/hr and are incompetent.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Not sure if I could use load tester. It's out in garage, but will have look at it tomorrow.

I have used same meter to check output of my 55A boat alternator when charging house batteries. Also checked output of our marine charger. In both cases readings were credible, but that was a while ago.

How about the 8-10A for the glow plugs when hot (value decreases the longer they are on). Is that credible? I might try that when engine is cold. I read that plugs + wiring measure about 1 ohms cold. So current should be 5x12/1.0=60A cold.

Meter does show a small current when everything is off. Those meters don't work well at low currents. Could just be draw from radio and clock. I can check leakage with DVM. Battery does not seem to run down anyway. Problem is just ultra slow cranking on occasion. But then everything is good again.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Glow plug should draw 8 A each full hot. X5 should be 40 amps. 5X your measured starter current is 100 A, which is more like it.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Found some more on glow plug resistance here

Seems like this is ending up to be a meter trouble shoot

Maybe I will have to read the meter manual or even check it's battery

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I did check again after putting new batteries into meter (old ones still seemed good) and re zeroing meter. I got much different numbers! Might be that last night I was working without much light and without my specs! I may have missed the decimal point!

I only did a rough check, but glow plugs registered close to 100A and starter with glow plugs in the 200A range.

Regardless, motor is spinning fine again. Connections at top are all good, but I have not yet attempted to get at connections on starter/solenoid.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

get new readings on the battery at idle, with engine just shut off, and after the car has sat for a few hours.

the numbers given didn't make sense... now I know why! good tools are the best at finding problems!

ok... if the 12.45v after sitting is right, your battery is shot. needs to stay above 12.65 below that, the battery is discharging, and needs replacement.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Car has not been driven nor battery recharged except for just before load test which was done twice.

Since then, the battery has been used to start car while doing testing 3 or 4 times and the glow plugs have been cycled about 6 times (and a load test was done twice). Battery voltage is now ~12.33.

I measured the leakage current using DVM on mA scale between ground cable and battery negative.It jumped around in 8-15mA range. Probably due to radio being connected. I guess I could pull a fuse, but I don't think the memory maintenance connection drawing current would be fused.

I tested battery acid SG. 5 cells were at 1.21 (middle of white band) and one slightly lower, maybe 1.20 (at edge of white band) Corresponds with 12.33 battery voltage and indicates battery is at about 62% charge. I need to redo once fully charged.

My battery is still under it's free replacement 9yr warranty but is 4 1/2 years old. They won't replace unless battery really IS bad. That's why I am doing these tests!

Next step is to recharge battery, then retest. Before that, I need to check alternator charging voltage/current with battery in present state.
Done. 13.77V, 7.2A. (13.3V, 3.3A after a 20 min drive)

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5