Hi guys,

Is it a known issue for a starting motor to gradually lose its cranking ability and taxing the battery in the process? Here's the rundown:

Cold start, a little difficult, voltage at battery (in trunk) drops to 10.6V but at the engine bay, it's dropping to about 9.2V. Whilst it has a difficult initial crank, it does pick up the pace with each revolution as though the motor itself were stuck and coming unstuck with each revolution of the starter motor. Odd stuff but I'm certain there's nothing wrong with the engine given it's only 110,000km old.

Measured across 300A fuse at battery and read a 0.4V drop.
Measured difference between battery and starter (on a battery voltage of 12.5V) and found a drop of 1.6V.
Measured difference between battery negative and body ground strap and found a negligible 0.05V drop.

So the action is on the +ve lead it seems but given I've tried another battery, I've even jumpered directly from the battery +ve to the engine bay +ve terminal and no change. This leads me to believe that there's a problem with the starter motor.

So, has anyone else experienced or seen this happen with starting getting progressively weaker and weaker? Just want to get everyone else's take on this before I decide to buy a new starter.

 

I'd put my money on a starter motor as well.
Try starting it while jumping off another vehicle, and see if it takes as long, that may lead you away from the starter motor being at fault....

 

That was going to be my next move. Since I have my original yellow top Optima (which obviously wasn't the problem - $300 gone to a red top for nothing!) charged up and waiting, I think I'll whip it out with a set of jumpers and see how we go with that.

 

The important bit of info there is "Measured difference between battery and starter (on a battery voltage of 12.5V) and found a drop of 1.6V"

Lets say under starting load your Bat voltage drops to 10.6V while the starter voltage measured is 9.2V and lets say your starter draws around 300A+ (typical), then you are feeding 300x9.2=2.8Kw to the starter to crack with while you are putting more than 15% of the available battery power out as heat along the length of pos cable (1.4x300=480W).

Go sort that cable and see to it that you have an adequate guage good quality wire there able to drop less than about 50W on the length of cable from the boot and your starting miseries will be solved.


................and all of that is only with the positive cable.

alsoI don't know if you are saying you actually effectively feeding the starter via the body, but I am willing to bet that the negative side suffers some energy loss of equal proportions because the "body" is not a real good conductor of starter sized currents.

If you want to prove all of that, remove the battery from the boot and dump it somewhere in the engine bay temporarily - fit serious jumpers to the starter poss terminal and engine metal itself - I will guarantee you have a completely different experience to " I've even jumpered directly from the battery +ve to the engine bay +ve terminal and no change. " .................. you have to do it properly



Moving the battery to the boot from its original engine bay location is often an exercise in futility if extreme care is not taken with quality cabling and connections and anybody suggesting you start replacing the starter without first sorting all the voltage drop issues simply don't know what they are talking about

 

LvR what about putting a capacitor in the starter circuit to supply proper voltage current to the starter while the battery remains in the trunk?

 

Nope - starter load way too big - no way around this one - have to fix the cables

 

I had a starter do that a few years ago as well.
Finally replaced it with a used OEM starter, and it cranked over twice as fast.

 

Actually, the starter draws under 100A according to the FSM. So if the starter is drawing anything greater than that, then there's something horribly wrong with the starter anyway. One thing I have not measured is the resistance across the cable or otherwise the current being drawn, as per Ohm's law, to determine one of those two values by calculation. Assuming the starter is not drawing more than 100A, the cable is exhibiting 1.2V / 100A = 0.012 ohms across the entire length which isn't all that bad along with the 0.4V / 100A across the fuse being 0.004 ohms so a total resistance of 0.016 ohms in that path.

Which couldn't possibly be happening as the cable is not even warm.

I overengineered that with 0GA welding lead. The insulation doesn't appear to have developed any defects along the entire length of it.


You're right. My bad there. I meant to say chassis ground, where we have the OEM ground lead that comes from the battery (if it were in the engine bay still), tied to the chassis rail and then continuing along to the engine. Point being, I grabbed more 0GA cable and jumpered directly from the battery's negative to the engine ground effectively and got no improvement so we know the grounding is fine.

As in my previous reply, that's what I intend to do next, even though I know that it should have worked with the 0GA jumper cable. If anything, that will be just for my own peace of mind.

As a matter of fact, the battery was relocated just over two years ago and totally reliable because I overengineered it in the first place, with the 0GA cabling on both feeds and solid 0GA ring terminals for welding gear, not some cheapie car audio bits. It's only in the past few months that it has developed this problem which is why I'm very confident in the set up after inspecting it and leaning towards the starter.

 

Not a chance. A cap is there only for rapid transient bursts of energy which is why they're only really useful for large stereo systems. Even if you had a bank of 10F caps or more, it still wouldn't be able to satisfy the amount of current drawn for that lengthy period of time (as it's not just a transient energy burst).

 

gotcha.. i know someone who has a trunk'd battery and a cap for their starter, but i don't give even 1/4 of a crap about car audio, so i don't bother to learn about the electronics behind it, or what else they could be used for

 

Mine did what you said in the original message for a long time then got slower and slower to the point it did the intermittent click sound and nothing. I replaced the starter with 2 reman units and they both failed - one burnt up in smoke. It depends on the source of the reman, but someone told me the reman units do have 'some' old internal compenents that don't get changed out, and they could pose problems.

Then I paid $190.00 Cash (I was sick of running around back and forth with another car) and got a brand new one with new solenoid and everything (WPS brand). It cranks so fast with so much power, that I can only just touch the key briefly in the start mode, where as if I hold it even 0.25 seconds too long it grinds the ring gear. Works perfectly since SEPT now.

Oh and my battery was ruined around the same time. I don't know if the dying starter caused it but it's posisble.

 

Indeed ............. but with no load.

Guess you never had a current probe on any starter before? - imo 300A during starting may actually be conservative - especially if you actually sort the voltage drop along the cable feeding the starter and have more voltage on the starter armature itself.
Well - how much copper is in those fat cables of yours and how long do you "crank" before giving up? - copper is one of the best heat conductors out there . Ever tried to calculate how long it would take that amount of copper to heat up appreciably (so you can feel a difference?) with an estimated input of 480W?

Now that you have posted ....................... I have to say that if you are so sure that your cabling is fine, how come the positive side shows a 1.4V drop to the starter but the negative cable don't - presumably the same "quality" setup?

IOW - if the one cable is so much better than the other don't you ask "why"?

Dropping 1.4V over any cable feeding the starter is bad news irrespective of the actual starting current drawn - your maths is fine to determine the cable length resistance, but you have no actual value on the current - power-wise the % lost power on the cable is directly proportional to the voltage loss over it meaning irrespective of the actual current measured you are still losing 15%+ of your starter's power/torque.

If you feel your cabling is up to snuff then fine - imo your "over-engineered" cabling/connectors needs a seeing-to to decrease the power loss there because that could very easily be the real reason why your starter may have packed it in if it turns out to be faulty now

 

Sorry, I stand corrected there. Took another look at the FSM and it did quote no-load figures.

Never needed to until now but I assumed that twice the amount of current would be drawn during cranking, hence, my choice of a 300A fuse at the battery.

Not if it isn't blowing the 300A fuse, surely?

As stated before 0GA, so 50mm^2.

I have. Now if the cable is not even warming up, that would suggest that the cable is not too thin for the task. In fact, it would take a long time for that amount of power lost through heat to actually become noticeable in a 0GA cable of 6m length. Given that for the 6m, the volumetric heat capacity of copper is about 1035J/K (from a starting temperature of approximately 25C), which would suggest 1035J per second or 1035W would need to pass through that cable to raise the temperature by just 1 degree in 1 second. So a cranking time of 3 seconds won't produce any noticeable change. Therefore, if the difference cannot be felt, the cable is well suited to the task and the voltage drop of 1.2V over the cable (not accounting for the 0.4V drop across the fuse) is for all intents and purposes something which would have appeared across the cable from over two years ago if it were not suitable at all when in fact it was presenting no more than 0.3V drop before this issue came to light.

Because I broke the rules and earthed the battery at two points, risking a possible ground loop - which did not occur in the end, thankfully. The battery -ve is tied to body ground at the rear (where that extra weight bar is in the middle of the trunk) as well as to the chassis ground in the front engine bay. Excessive, perhaps but since we both agree that body ground is a more resistive path than chassis ground, that was my basis for deeming it necessary.

Therefore, the losses experienced would be far less for the -ve side as opposed to the +ve side.

After trying out the other battery jumpered as close as possible to the starter motor this morning on the cold start and then this afternoon after returning home from work, I've had the same results.

Prior to this problem, the vehicle always exhibited a starting voltage of no lower than 10.2V so if anything, I was losing approximately 0.3V. That to me suggests that my cabling at least was up to scratch at the time. Having inspected it, nothing has changed. Therefore, I'm of the view it's not the cabling that caused the death of a 16 year old starter motor. Especially after today's test and the previous test of jumpering another run of 0GA cable from the rear battery to the front, effectively forming a 2/0GA +ve cable, making no change to the situation it looks all the more like a bad starter.

I just wanted to hear from others who may have had a similar experience. I should have also mentioned that when the car is hot, starting it is almost impossible until it has cooled down. I guess I was a little hasty in my original message but after checking the terminations and making sure there wasn't any expansion taking place, that's what happens.

I appreciate your suggestions and have taken them on board though I think you need to be a little more tactful in your responses in some parts. Like this for example:

Unless you're absolutely aware of the entire situation (and clearly you weren't since I admittedly neglected to mention the extra details noted in this message), it's one thing to say that you're confident it's a cabling issue and another thing to say that it can only be the cabling and everyone else is a fool.

Anyways, thanks for your help. I'll start looking for the spare starter motor I hopefully have. Otherwise, time for a brand new one.

 

Hi all,

Quick update. Found my spare starter motor (about 8 years old at the time of its removal). Cleaned it up and bolted it on. Starts are back to their usual crispiness. Found the battery terminal/bolt of the magnetic switch is loose in its fitting so that's the first suspect but there could be more to it inside.

At any rate, I doubt it would be worth getting this one repaired though I might get my auto electrician to check it out for me anyway and if it's no good, I'll buy a new starter motor as a spare anyway.

Now the only thing left to do is to get a thread repair kit for the bottom bolt. When I removed the bolt to get the starter off, I found bits of alloy in the threads. DAMMIT!!!!

Since so many of you here have been so helpful (with the exception of one, not to mention names), I can't be bothered taking the bottom bolt off to measure it up right now ... any ideas what size and thread the bolt is?