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  #1  
Old 04-30-2022, 11:44 AM
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2007 X5 4.8l slow crank especially hot

I'm at about 97000 miles with very low usage currently, in a well maintained X5, but having a new problem.

I am just barely over 3 years on a new battery (39 months), and starting to have issues starting. I am in S. Florida so used to batteries not lasting long, but this is garage kept and a bit young to be dying.

The symptom is slow cranking, which gets worse if the car is hot. Last time out I made 3 stops over about 6 miles and the last time (after sitting maybe 20 minutes) I really did not think it was going to start.

Took it to the shop, they said the battery tested good (800+ cranking amps), they spent a long time and two computers without finding anything in specific wrong, other than my trips are too short and infrequent to give it a good charge. I know that, and always put a trickle charge (2A) on so the battery is topped off when I leave.

They suggested the starter may be failing; I am only familiar with starts that seize or just fail open, not one that gets weak, is that an expected failure mode?

Last time I parked it after a long drive I monitored voltage under the hood over 4 days with no charger, it went from 13.06 to 12.95v, so there is no unexpected drain. When the car is in a warmup mode (e.g. open the door) the voltage at the front drops to about 12.6, presumably from all the computers starting up though a larger drop than I would expect. But I have no idea what is "normal" in that case (anyone ever checked? E.g. car off, hit the start button again so radios, etc. go off, but other systems still active).

My inclination is to put in a new battery even through 3 years is pretty young even in Florida for garage kept.

But 100k miles also says maybe I do have a starter issue. But do they fail slowly by starting slowly?

Advice welcomed.

By the way, the repair shop said make an appointment to leave it, and they would do further testing (this was a courtesy check while I waited - nice folks, have used them for a while). But I wanted to do some homework first.

Thanks for any advice/experience.

Linwood
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  #2  
Old 04-30-2022, 12:16 PM
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I'd start addressing your issues with the change of the ground straps.
Cheers!
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  #3  
Old 04-30-2022, 12:20 PM
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Specific places? I have done little service personally on the car, are they fairly accessible, or something I need to get a shop with a lift to do?
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Old 04-30-2022, 12:46 PM
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OK, I did some reading and found the recommendation to test by grounding from a good frame ground to the engine with jumper cables. Did that, and no real change in how well it starts, so it sounds like that may not be the cause?
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Old 04-30-2022, 12:51 PM
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To test the ground strap measure voltage from the engine block to the negative jump bolt on the fender while cranking. It should be far less than a volt.

Also: get a measurement of the current draw on the starter. A common failure is the starter will take far more current as it fails. The increase in current provides far less torque combined with the voltage drop at the battery due to the increased current. Very often people incorrectly diagnos the battery not the starter as the fault.

One more possible fault: the B+ jump point it can get loose and be a very high resistance that will cause your symptoms.
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Old 04-30-2022, 01:48 PM
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I'll need to get someone to help, or take it back to the shop. I did measure the resistance (I realize not a good test since that's done at such low current) and got a very near zero between engine and frame.

All the connections I can readily get to, on the battery and the jump points, are solid feeling and no visible corrosion (though I think the main engine one is out of sight without a lift).

So if a starter can have higher draw and lower torque as it fails, does that get worse with heat? I'm trying to reconcile that this problem is much worse as the engine gets hot, meaning it turns over much slower; it starts very quickly regardless once it turns over, it does not seem like any kind of engine problem, it is about getting adequate turnover on start.

Is 100k miles a reasonable lifetime for a starter on this car? And 15 years.
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Old 04-30-2022, 03:05 PM
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Mine failed about 160,000.

There are a few good reasons for heat to be involved mostly that something is either opening or shorting inside the starter motor when hot and not when cold. Also the B+ terminal may be loose when hot not when cold that's an easy one to check.

Resistance across the ground strap is very hard to measure.

0.1 Ω would be a terrible value.

(200A * .1 Ω = 20v (out of 12)

.01 Ω means 2V lost. It really needs to be on the order of 0.005 Ω. Something that you can't directly read in ohms.
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Old 04-30-2022, 03:26 PM
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Quote:
Originally Posted by andrewwynn View Post
Mine failed about 160,000.
Resistance across the ground strap is very hard to measure.
That's why I didn't mention that at first, measuring with a DVOM meter is not very meaningful.

I've checked the fit and visual state of everything I can see, I think it needs to go back into the shop. I am reasonably convinced at this point it's the starter but with a possibility a ground strap I cannot see, but I think further testing takes two people (or a recording meter which I do not have), and probably a lift as I think the main engine strap is underneath. I have digital detailed system manuals (not sure what they called them) but so far have not found anything to show the grounding cables for the engine.
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Old 04-30-2022, 09:20 PM
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Two things you can. Do with a DMM:

1) measure voltage from B- jump bolt on the fender to the engine block while starting. It should be well under a volt.

2) measure the voltage from the positive of the "cigarette port" to the B+ while cranking the car. That value should be about 1/300 of the starter current. Eg .75*300=225A.

It helped greatly if your dmm measures peak reading.
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  #10  
Old 05-01-2022, 01:21 PM
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Thank you.

I did the B- to Engine, and got 90mv when starting, so well under 1v.

For reasons unclear neither cigarette port is working, even with the car started (testing center to ground). Probably a fuse blown somewhere, I never use them, they could be simply broken as well. It was more than I had time for to troubleshoot and/or find another good 12v interior source. I may be able to reach a jumper cable from the battery to the B+ back near the battery and clamp onto it with the DVOM (which does have a max display). But more than I had time for, have to run out for a while.

But the 90mv to me seems like a good indication the engine ground is solid, and the positive line from the battery is insulated all the way and less likely to be corroded (and I've already checked the battery terminals, clean and solid).
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