How many amp Alt needed with Jeep fan mod?

[Arl37]

69 C10 with 350 crate HEI auto trans and no AC. Installed Jeep Fan mod and now when ever fan kicks on the needle on voltage gauge pops over to max as long as fan is running. Gauge is original. 195 thermostat and 195 temp sensor for gauge. Fan runs pretty much all the time once it kicks on. Fan supposedly draws 30 amp. Have 78 amp alternator from 93 Silverado. ( Got that alt off forum as recommendation). Before fan mod, gauge was in middle of gauge pretty much all the time. Afraid my alt is not keeping up with draw and battery not fully charging.
What size amp do I need with jeep fan?

[Jonlopes]

My favorite alternator mod Is to add a 12SI unit from a 1985 Buick Regal. They are a very easy mod, have a 9:00 wire orientation and the 85 Regal had a 94 amp option that costs $75 at Pep Boys. Summit has a $18 conversion kit to mod the external regulator alt to the 12si internal.

You have to remember that a 78 amp alternator puts out that amperage while spinning at highway speeds. I am not sure what it will put out at idle but you may end up draining the battery if you are in stop and go traffic.

My question is if you have a 195 thermostat it will not let the engine go below that temp so if your fan temp sensor is set to kick in at 195 that is probably why the fan is on all the time. I would either set the fan at 205 or run a 180 degree thermostat.

[RichardJ]

A 93 Silverado would have had a CS130 with 104 Amps or higher. Next generation after the SI alternators.

The original gauge on your C10 is an Ammeter, not a volt meter.
With a hand held voltmeter, measure the battery voltage at the battery.

[Arl37]

RichardJ- My typo. Is is an alt for a 83 Silverado

Johnlopes-The only way to set the fan for 205 would be to have a 205 sensor in the block. I can put a 180 thermostat in but would the fan ever come on?

[Jonlopes]

Originally Posted by Arl37

RichardJ- My typo. Is is an alt for a 83 Silverado

Johnlopes-The only way to set the fan for 205 would be to have a 205 sensor in the block. I can put a 180 thermostat in but would the fan ever come on?

The thermostat is a mechanical switch. Right now below 195 your current thermostat is closed stopping all water flow and allowing your engine to heat up. Once it reaches 195 it opens allowing the water to run through the radiator cooling the engine. If the radiator is able to cool the engine to a temp below 195 the thermostat will close starting the process again. through the open/close/open process the engine will always be at 195 or higher. The switch on the fan if it is set to 195 would never see the water temp go much below 195 because the thermostat will not allow it. This is why your fan is on all of the time.

If you install a 180 degree thermostat it will open at 180 degrees (15 degrees cooler) and will not let the engine go below 180 in the same process as above. With this thermostat if the temperature is between 180 and 194 the fan will not turn on because your motor is running at a safe operating temperature. If you go above 195 it will turn on and run until you are below 195 again and it will turn off.

I hope I was clear in explaining this. if not please let me know.

[Jonlopes]

Also if you have the alternator from an 83 truck then the Buick alternator will fit right in, you cannot tell it apart from the housing or the way it mounts electrically or mechanically.

If you want to upgrade to higher amps just go into Pep Boys (or any other auto parts store) tell them you have an 1985 Buick Regal, any engine, with the 94 amp alternator. You can give them your current unit for the core if you want or just eat the approx. $10 core fee if you want to keep it as a back up.

[67 chevelle]

Originally Posted by RichardJ

A 93 Silverado would have had a CS130 with 104 Amps or higher. Next generation after the SI alternators.

The original gauge on your C10 is an Ammeter, not a volt meter.
With a hand held voltmeter, measure the battery voltage at the battery.

My thoughts exactly , the whole truck system probably pulled less amps in 69 than that fan by its self ,, would peg the gauge ,, check volts at fuse panel ,, many have converted to volt meters ,, hows your headlights look with the fan running

[RichardJ]

First he needs to find out if he needs a bigger alternator. A bigger alternator will not give a lower Amp reading.
Only if the alternator can't supply the proper voltage at the battery would he need a larger alternator.

I don't know what " Jeep Fan mod" he is talking about. A 30 Amp fan would only draw 30Amps at startup for 1/2 second, then drop to 15-18 Amps.
Need to know battery voltage before and after fan kicks in and how it is wired. Would also be nice to know the specifics of the SI installation wiring.

[Jonlopes]

I am not sure what he is using but I have been using this type of conversion kit for over 20 years with no issues at all. Could not be easier

http://www.summitracing.com/parts/aww-27555

[Arl37]

Jonlopes- My thoughts exactly on using a 180 thermostat. Called Painless and they also said that was the solution.
JRichard- On this site google "another cheap fan mod". will tell you all about "Jeep fan mod"
Initial question was do I need a bigger alternator. I would say yes from responses and will either get the Buick or have a local shop build me a 100 plus amp alternator.

Thanks to all for your help.

[71meangreenc10]

My 2 cents.

I have done the MOD and here is what I have found. I have AC also and wired in a pusher fan on the condensor. When you hit the AC, both my fans kick on. With the AC on, lights on, HEI, fan at full speed, I measured about 62 (will have to verify that again, may have been 22) Amps with a Amp Clamp on the Alt. My Alt is from a 92 GMC so it puts out over 100 AMPS. If you decide to put in a 100 AMP Alt, ensure you check the red wire that goes across the radiator to the battery for over heating. I found mine by accident and it was really hot, I upgraded the wiring to either 10/12G wiring and no more issues. I have good grounds and a lot of newer wiring, so there was no corrosion build up in the wiring.

I can get you the part number for the adjustable relay I used for the fan. It is a very nice piece from Summit and it allows you to add in other circuits if needed.

Smitty

[71meangreenc10]

Originally Posted by RichardJ

First he needs to find out if he needs a bigger alternator. A bigger alternator will not give a lower Amp reading.
Only if the alternator can't supply the proper voltage at the battery would he need a larger alternator.

I don't know what " Jeep Fan mod" he is talking about. A 30 Amp fan would only draw 30Amps at startup for 1/2 second, then drop to 15-18 Amps.
Need to know battery voltage before and after fan kicks in and how it is wired. Would also be nice to know the specifics of the SI installation wiring.

Here is the Mod RichardJ.

http://67-72chevytrucks.com/vboard/s...d.php?t=254617