wwilme

My 1997 4Runner 3.4L w/ 235k trouble free miles is showing signs of what might be a bad alternator. After sitting for not very long it is slow to crank. I had the battery (35/72 months) checked at NTB last night and they said it was still fine. That leaves the alternator. Every other vehicle I've had with a failing alternator has showed a glowing dash light indicator. The dash light does work - I checked. I have an elcheapo plug-in-cigarette lighter "battery/alternator condition analyzer” that lights up showing a slow charge. No idea if this thing is even worth acknowledging.

Some other threads have suggested cleaning the wire contacts going into the alternator with CRC and/or replacing brushes. Regardless, I'll be doing the labor myself, but I can't help thinking that any auto parts place I go to will tell me that of course the entire alternator is shot. With so many miles on the vehicle, is it worth just cleaning or rebrushing, or is something else in the alternator likely to go soon? Any advice appreciated!

quattro

Alternators are cheap relative to getting stuck and having an expesive tow to get to service. I'd say swap it with a replacement unit. If you're strapped for cash check prices at a yard on a used sub-100k mile unit, else get a reman unit.

Rick F.

Something doesn't add up... it's slow to crank AND the battery is good (by "good" I'm assuming also fully charged...)...

The alternator has NO role in cranking the engine other than ensuring that the battery is charged. . Regardless, if you've never replaced the alternator, then you're overdue. Replace it anyway! Even if it's not bad, it's probably not long for this world.

MTL_4runner

Slow cranking on startup can be a few things, but I doubt the alternator is at fault there. Most often slow cranking is an indicator the battery may soon fail (that doesn't mean it won't load test ok at the time). Other possibilities may be corroded or broken battery cables, the starter armature or other source of battery drain. You can check your alternator with a digital multimeter, it should remain above 14V at 3k RPM with all the acessories on (fans, AC, highbeams, etc) at the battery terminals.

wwilme

The battery place put a tester on it and it had plenty of cold cranking amps. They said it must be the alternator or a bad connection. Last night I took the terminals off, cleaned them and the battery posts, checked the cables for wear and put them back on. Then I tried a cheapo testor I had lying around and it said battery - ok, alternator - low charge. I should go get a real test done on the battery and alternator. To me, it makes sense that if the alternator is is failing, it would not charge the battery fully.

MTL_4runner

What voltage did you see on your DMM?
Was that under load?
What was the engine RPM?

Sure you can take them out and bring them over to a shop for testing but using a DMM under the correct conditions can be alot easier.

wwilme

It wasn't a DMM, it was cheapo thing I've had lying around the garage that you plug into the cigarette lighter. A combination of little lights tell you the condition of the battery and alternator. Looks like a typical plug in house electrical outlet tester - one of those things that tells you open ground, etc. I need to get a real tester or stop by a garage.

Rick F.

Do as MTL_4Runner suggests and get an inexpensive DVM. Heck, Radio Shack has 'em for under $15. They're good to have anyway... A simple voltage test with as much load as you can put on the alternator should help, if not resolve, what the problem is. I'd put $$ on the alternator, but no sense replacing it without having more basis (with the exception of my previous post that it's probably near end-of-life anyway...).

frodin1

If you have a battery place check your battery,see if they have a refractometer,and or a load tester.Load testing alone will be give you a true test.Voltmeters will tell you it's charging but if your battery has a low gravity it won't do you any good.By the way if you mention a refractometer to most people they wont know what your talking about.They're aroud $250 bucks for a good one!

MTL_4runner

My brother just had a similar issue with his car slow cranking and eventually it ended up being a combination of things, but the first thing I told him to do was to go get himself a good multimeter and he found this at Sears (I tried it when he finally came up to visit and it's very decent for the price). He first tested it at idle with no load and got 13.8V so I then told him to put a load on the alternator (turning on all the items in the car....esp highbeams put alot of load on it) and he got about 13.3V which to me is usually the sign of a dying battery (ie fairly heavy alternator load). So about 2/3 of the way up to visit me he had a new battery installed and about 3/4 of the way up his car completely broke down, no power at all in the car. We got it towed up to my house and I immediately put the new battery back on a charger. Tried to start the car the next day and it fired right up but now it only read 12.48V with the engine running (RPMs had no effect on voltage so we knew the alternator was toast). Well, on his car it ended up being a dying battery (BTW, that is the #1 cause of alternators going bad, by far, on a lower mileage vehicle......ask any auto-electric motor service technician) starting the domino effect, but that battery drawing a constant load also fried his alternator later since he waited too long to change it. So now we are getting it all fixed for him this week for his trip back to the US (also auto-electric motor service places are great at doing alternator/starter rebuilds super cheap if the stator is in good condition).

I was lucky to actually able to rebuild the alternator myself (bought the correct Hitachi brushes from the autoelectric motor service place.....bearings were in good shape and felt smooth when spun) by just replacing the brushes because they wanted crazy money for a rebuilt alternator for these Subaru Outback vehicles with a 2.5L motor (I got one price of $850 CDN from the dealer for a new part and $500 for a rebuild)! The design on the alternator was pretty poor because it had plastic brushholders which obviously melt at high temps (created under heavy loads like charging a dying battery). Thus the brushes began to stick where they should slide free and no longer made good contact with the stator field rings. Soldered out the old brushes, cleaned out the slides with a small file and soldered the new ones back into place. I also had my brother pick up a spare from a junkyard (ask them for the mileage since some actually put the mileage next to the part listing......ended up getting one with about 43k miles for about $135 CDN) for the trip home. If you have a spare this would be an easy roadside repair. Only thing subaru did right was to put the alternator right on top of the motor so changing one is a snap. He made it the full 10 hr drive home and the alt still showed 14.4V at the end of the trip....success!