100 amp C3 alternator

[Michael B.]

Hi all

diagnosed my supposed "hot starter" issue to actually the drain from the dewitts dual spal fans. Had a meter running and even at speed when the fans kick in the alternator doesn't keep up. Voltage can easily drop toward 12v and lower with the headlights on. I had just replaced the starter a week earlier only to have the same thing happen a week later.

Can any one suggest a quality direct fit 100amp alternator. Is there a particular year that might have been a direct fit for a 77.

Thanks all.

Michael B.

[Michael B.]

Re: 100 amp C3 alternator

I was reviewing the thread (amongst others)
"GM one wire alternator for addition of electric fan on radiator for cooling"
which was very helpful. Its focused on the previous generation but covers a larger range of alternators. In checking the assembly manual there is no greater current amp normally available but it appears some 10si after market alternators are available. In some cases it looks like they've shoe-horned in 100+ amps into the original 10si case. Anyone able to make recommendations on a good one?

But there is a followup problem that was a very good point Duke brought up about placing the fan connections directly on the alternator to avoid running the additional current through the original wiring. Given I rewired like original using Lectrics harness I doubt this was meant to run the current from the fans. At the moment I run the fans through the starter battery binding post. This way it can run from a source with the greatest current on a large gauge wire. My concern is that in those times when the charger is not going to keep up attaching to the alternator battery lead will then have a much smaller gauge wire being back-fed that higher current from the battery. Which is worse/better?

One other approach I considered was pulling the fuse on one fan because I doubt I can over heat with this aluminum rad and the fan boost but I could be wrong.

Thanks for you guidance

Michael B.

[Michael W.]

Re: 100 amp C3 alternator

I'd go on a different tangent and find out why the engine cannot be cooled adequately with a stock fan and clutch.

[Michael B.]

Re: 100 amp C3 alternator

I'd go on a different tangent and find out why the engine cannot be cooled adequately with a stock fan and clutch.

During worst case scenarios, mostly when stuck in traffic, the original config could see temperatures go frighteningly high to the extent cabin heat was turned on to bleed off heat. I don't think this year was unique. The rad, fan and clutch are hanging on the wall should I decide to go back. This was a drivability decision when the car was fully restored. Aint goin' back ! But thanks for the thought.

[Michael W.]

Re: 100 amp C3 alternator

During worst case scenarios, mostly when stuck in traffic, the original config could see temperatures go frighteningly high to the extent cabin heat was turned on to bleed off heat. I don't think this year was unique.

'77 models were not known for doing that when new. Somethings amiss.

[Joe L.]

Re: 100 amp C3 alternator

I was reviewing the thread (amongst others)
"GM one wire alternator for addition of electric fan on radiator for cooling"
which was very helpful. Its focused on the previous generation but covers a larger range of alternators. In checking the assembly manual there is no greater current amp normally available but it appears some 10si after market alternators are available. In some cases it looks like they've shoe-horned in 100+ amps into the original 10si case. Anyone able to make recommendations on a good one?

But there is a followup problem that was a very good point Duke brought up about placing the fan connections directly on the alternator to avoid running the additional current through the original wiring. Given I rewired like original using Lectrics harness I doubt this was meant to run the current from the fans. At the moment I run the fans through the starter battery binding post. This way it can run from a source with the greatest current on a large gauge wire. My concern is that in those times when the charger is not going to keep up attaching to the alternator battery lead will then have a much smaller gauge wire being back-fed that higher current from the battery. Which is worse/better?

One other approach I considered was pulling the fuse on one fan because I doubt I can over heat with this aluminum rad and the fan boost but I could be wrong.

Thanks for you guidance

Michael B.

Michael-------

First of all, no C3 ever originally used an alternator as large as 100 amp. So, there's no alternator which could be "borrowed" from another C3 and be a "drop in" replacement. C4 Corvettes did use alternators of about 100 amp and larger. However, whether they could be adapted to a C3, I do not know. Such adaptations, though, can open up a "can of worms" that will have many other "ramifications". As far as aftermarket "souped up" alternators in a 10SI or 12SI case, I wouldn't touch one with a 10 foot pole.

As Mike Ward suggested, I think you need to get at the root of your cooling problem rather than put a "band-aid" on it by adding electric fans. There is no good reason that you should not be able to cool your application with the stock radiator, fan, and clutch. The radiator used for your application is about the same size as that used for 1969-74 big blocks. So, if they could cool those applications, they should definitely be able to cool yours. However, you could upgrade your cooling system without having to resort to electric cooling fans. Install a DeWitts "Direct Fit" aluminum radiator and you will gain about 35% additional cooling capacity. This radiator will appear very much like your original radiator. DeWitts even has a "heavy duty" version of this radiator which will provide additional cooling capacity, not that you should really need it.

Use your original fan blade assembly in conjunction with a GM #88961768 fan clutch and your idle/low speed cooling problems will be over.

If you can't obtain satisfactory cooling with the above-referenced set-up (if not your original radiator, fan, and fan clutch in good condition), then you've got some other problem that needs to be addressed. Electric cooling fans will not address it.

By the way, the most common problem resulting in cooling insufficiency is a radiator that is plugged or otherwise degraded.

[Rick A.]

Re: 100 amp C3 alternator

check heater core also - many people will do everything Joe/Mike point to and then do NOT do a complete flush to include the heater core

[Gene M.]

Re: 100 amp C3 alternator

Mike,
If you want 105 amp alternator with internal regulator DB electric produces some excellent products contrary to others on this board opinions. But be advised by me you should up grade the stock wire harness to match up with the added output and new configuration. It was advised to find the issue preventing the stock set up has for not cooling the engine. That is good advice. Adding electric fans is a band aide. If you added aftermarket air conditioning then yes more current and cooling capacity is necessary. The stock 37 amp unit is marginal at best with everything running on the car. It was then and still is now. Lights, blower, radio, wipers all running at low speed is hell on the stock 37 amp alternator. Short trips and restarting just makes the bad situation worse. Do more research prior to changes.

[Mark E.]

Re: 100 amp C3 alternator

I agree with Michael, Joe et. al.

It's risky to push 100 amps through a harness not designed for it. This fix may shift the problem from overheating to flaming.

[Michael B.]

Re: 100 amp C3 alternator

Wow, this frustrating. Thought this would be easy. Greatly appreciate the responses from everyone.
The rad and the heater core are new, as is the engine (rebuilt) when everything was restored. The issue has nothing to do with a problem since rebuilt. It had everything to do with rebuilding a driveable vette that retained as much originality as possible. The dewitts kit was to address that.

It's pretty obvious if I go to the bigger charger I need to bolster the positive lead which I really don't want to do on this beautiful new harness. And I never knew about the better clutch mentioned by Joe (was that for the L82 or just a better GM replacement). So I'd have to ditch the electric fans, put a new shroud in (accounting for the the thicker aluminum rad - which I'm guessing is an L82 setup) and the problem would be solved and look near original again.

Thanks for the suggestions.

[Gene M.]

Re: 100 amp C3 alternator

Wow, this frustrating. Thought this would be easy. Greatly appreciate the responses from everyone.
The rad and the heater core are new, as is the engine (rebuilt) when everything was restored. The issue has nothing to do with a problem since rebuilt. It had everything to do with rebuilding a driveable vette that retained as much originality as possible. The dewitts kit was to address that.


It's pretty obvious if I go to the bigger charger I need to bolster the positive lead which I really don't want to do on this beautiful new harness. And I never knew about the better clutch mentioned by Joe (was that for the L82 or just a better GM replacement). So I'd have to ditch the electric fans, put a new shroud in (accounting for the the thicker aluminum rad - which I'm guessing is an L82 setup) and the problem would be solved and look near original again.

Thanks for the suggestions.

You will need to upgrade the entire under hood harness not just the positive cable. Understand a single wire alternator is NOT the way to go. You would loose a lot of the self controlling functions of voltage regulation. As I said prior do more research prior to changes. There is tons of information on the inter web.

[Joe L.]

Re: 100 amp C3 alternator

Wow, this frustrating. Thought this would be easy. Greatly appreciate the responses from everyone.
The rad and the heater core are new, as is the engine (rebuilt) when everything was restored. The issue has nothing to do with a problem since rebuilt. It had everything to do with rebuilding a driveable vette that retained as much originality as possible. The dewitts kit was to address that.

It's pretty obvious if I go to the bigger charger I need to bolster the positive lead which I really don't want to do on this beautiful new harness. And I never knew about the better clutch mentioned by Joe (was that for the L82 or just a better GM replacement). So I'd have to ditch the electric fans, put a new shroud in (accounting for the the thicker aluminum rad - which I'm guessing is an L82 setup) and the problem would be solved and look near original again.

Thanks for the suggestions.

Michael-------

The predecessor for the fan clutch I previously mentioned was used for 1977 Corvettes with L-82 AND C-60. It was not used for L-82 without C-60, though, although it could be so-used. The part number I mentioned is basically the same as the original except it has a dual bolt pattern hub.

A stock 1977 fan shroud will work with the DeWitts "Direct Fit" aluminum radiator. Its size and configuration is the same as the stock radiator.

[Michael B.]

Re: 100 amp C3 alternator

Michael-------

The predecessor for the fan clutch I previously mentioned was used for 1977 Corvettes with L-82 AND C-60. It was not used for L-82 without C-60, though, although it could be so-used. The part number I mentioned is basically the same as the original except it has a dual bolt pattern hub.

A stock 1977 fan shroud will work with the DeWitts "Direct Fit" aluminum radiator. Its size and configuration is the same as the stock radiator.

Thanks Joe.

[Michael B.]

Re: 100 amp C3 alternator

The fan clutch has been ordered.
Does anyone happen to know an appropriate plug to replace the temperature switch on the dewitts rad.

Thanks again.

[Michael B.]

Re: 100 amp C3 alternator

I'm resurrecting this post just to get some quick insights about insertion of the original fan shroud.
I've removed the spal fan assembly and the rad sensor so all the electricals and original (new style) clutch fan are in place.
Before placing the fan/clutch on I couldn't see how the shroud could go on. I'm wondering what's the minimum equipment to remove to get the shroud back on. Looks like the water pump pulley might have to come off but want to check before I start ripping apart more than I have to in case someone has a technique I can't readily see.

By the way, with the new clutch/fan assembly, the Dewitts rad and without the shroud the temperature barely broke 150f. Love hearing the fan growl again.

Thanks all for the guidance.

Michael B.