79 924 porsche charging issues

Question

MY 79 924 2.0

History: this spring

removed engine, rear main seal, clutch, oil pan gasket, A/C pump removal

Summer

head gasket blew and replaced with valve guides, valve cover gasket and valve clearance reset

new battery and rebuilt known good alternator along with new alternator mounting bushings.

Symptom.

charging at 12.6 at idle voltmeter on battery and on gauge in car.

with all accessories on it dips to 11.4 (heater fan, rear window fog, LED headlights and fog). turn signals make it really dip.

Engine temp gauge climbs quickly while the charging is at 12.6v-11.4v but the fans do not turn on. pegs out at HOT

oil pressure is Normal in all instances on gauge. It charged normally before I started the clutch/head gasket. It would charge intermittently with normal temp setting. (the reason to check Alt and Battery Issue)

I've checked the connection to the temp sensor on back of head and it is connected.

driver fan worked when jumped at radiator fan switch albeit noisy at start.

Passenger side worked quietly with battery jump

open circuit on radiator fan switch when cold.

fans did not come on when i turned on the A/C. (normally do)

I'm headed out to pull the battery/starter/alt cable for testing. tested ok 14.2V at Alt 12.1V at battery..

Any ideas are going to be appreciated

Doc · Accepted Answer

I agree with Heyinway, sounds like a poorly rebuilt alternator, or bad voltage regulator (internal). With a meter on the battery, your should be getting 14-16v when you idle up. Also, check all major grounding points, battery to body, engine block to body, etc., for looseness or corrosion.

heyinway · Answer

Battery voltage is too low, it may have a bad cell.

I've had new batteries that tested bad before installation. Engine off...fully charged battery voltage should be close to 13 volts with a new battery...no matter where in electrical system you check. Engine on...turning on all 12 volt items, the alternator should constantly maintain no less than what the battery is with engine off.

Ensure that alternator has a good ground. Alternator is putting out minimum voltage...and likely not much amperage. This failure can happen when alternator is trying to charge a dead battery...alternator internal components overheat and fail. In your case, it probably a bad rebuild to start with.

Anything 12 volt that is trying to operate at less than 12 volts and enough amperage is going to overheat and fail. Same happens with too high voltage and amperage. It has to be within a narrow range of both.

nillezeiger · Answer

replaced engine to body ground   Problem solved

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[Solved] 79 924 porsche charging issues