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booneylander

451 Killing Alternators

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So on one of our 451s we have been running, we've killed it's second alternator in about 20k km. At first, when I got the car and we started driving it, I would notice that the headlights would dim when the car was changing gears. Not much, like, not enough for my SO to notice it, but I would notice it. I never really thought much of it until the alternator up and died. So fine, I swapped in a spare alternator I had from a parts car. While I was at it I removed/cleaned/reinstalled the ground strap and checked continuity from the battery neg terminal to the engine block (had no resistance before fiddling, and after as well). With the new alternator installed the headlights wouldn't dim anymore on shifts and everything seemed good. Now the replacement alternator has gone as well. 

So I'm wondering if anyone's experienced something similar? I'm wondering if there might be an issue with something else drawing too much current, or if there's anything on the control side of things (SAM?) that I might check to look for issues that might be causing the alternator to over/under charge or...

I'm going to try a few more things while I'm at it but I'm out of spare alternators which means the next one is going to be out of pocket and I'd rather not have to keep replacing them.

For what it's worth, on one of my 450s I killed a couple alternators, but in that case I had an aftermarket under-seat subwoofer to blame, which, once unhooked, solved the issue. Unfortunately no such devices to blame in the 451.

Edited by booneylander

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Can you install a good voltmeter and have it where you can see it while driving to see if and when there is a heavy draw on the system? What does the altenator normally charge at compared to a constant draw on it? What does it spike at or is it a constant draw?  Until you install something to show you this info you'll never figure it out imho....and I hate electronics....why would i buy this car then....lol.     It'll force me to learn more about the electronic side of it I'm sure.

 

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With the factory battery my lights would dim noticeably when shifting.  Alternator went at 180k km.  With an aftermarket battery and the rebuilt alternator, the lights do not dim to the same degree.

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22 minutes ago, Willys said:

Can you install a good voltmeter and have it where you can see it while driving to see if and when there is a heavy draw on the system? What does the altenator normally charge at compared to a constant draw on it? What does it spike at or is it a constant draw?  Until you install something to show you this info you'll never figure it out imho....and I hate electronics....why would i buy this car then....lol.     It'll force me to learn more about the electronic side of it I'm sure.

 

 

I had my voltmeter in the car just on the seat when I test drove the car after swapping the alternator. A good long drive and charging was normal - 14.3-14.5V at most all times.

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When the alternator on my 451 died I did a lot of looking around the web and it seems the average life of one is about 100,000km. Which was where mine quit. But 20k seems very short though you say it came from a parts car so perhaps it too was on the way out. I agree with Willys in that you should put a good voltmeter on the system and see what is going on. How old is the battery? 

 

One weird thing with my smart, my head and taillights come on automatically when I start the car even though my stalk switch is off. And I just double checked and I don't have a US car with auto headlights as my stalk only has 3 positions.

 

Since you pulled the old alternator did you get it rebuilt? That might be worth it vs trying to find a used one. Granted I bought two spares online, one came from a wrecker in Quebec and looked brand new and price was good so that is another thought, suspect the dealer is going to be horrifically expensive.

 

When my alternator bought it, we discovered that the belt tensioner was also seizing up so you might want to look at it when you are at it.  But and this is a big one, I used a new one from NAPA which failed within 1000km and because I didn't make the connection that I had also lost my fan belt I overheated my motor and blew my head gasket. A very expensive and time consuming mistake. The odd thing with the NAPA part is it was the same casting as the original but had the MB part number filed off.

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With my 451 my lights would dim with the factory battery.  I threw that battery out the first year I had it and put in a group 34 virgin lead AGM.  No more head light dimming or any alternator troubles in 140,000klm.  My theory is that those voltage drops are whats killing peoples alternators.  

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That's why I asked about the voltage meter and watching the readings....is the altenator charging full all the time? Does it have to because the battery is being over loaded so to speak? OR is there something drawing too much that the whole system can't keep up? Is the battery bank or storage quantity large enough to deal with the needs from the car.causing the altenator to constantly struggle to keep the battery up to where it wants it?

 

Like I said i hate electronics, I need something to put into my head for me to see it  so to speak.....I'm a hands-on learner  so to speak....lol...

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When I had the belt off I checked the tensioner pulley to be sure it was spinning freely, and it seemed fine. Might be worth changing it completely as preventative anyway.

It's certainly possible that the "spare" was on the way out too.

The battery is only a couple years old, Interstate. And it starts the car like a champ every time, so I'd be surprised if it was causing an issue, but you never know.

I'll run the scangauge in the car for a while after I replace the alt, so I can monitor voltage over long periods and see if I can find anything that might pull the voltage way down like turning on the heater fan, wipers, etc... something that's pulling way more juice than it normally should. 

The plan is to pull it and take both it and the old one I took out in to be rebuilt so I'll have a spare for later. Will be interested to see what if anything the rebuilder says about what went wrong with them.

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Mine drops about a volt when it shifts, headlights did flicker as well, I install a large capacitor at the battery, that seemed to fix the problem.

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