Voltage drop when car is warm?

[Nik0las]

Hi

Friend of mine has strange issue with the volatage. On cold start perfect voltage 14.5++ no issues with turn lights or heaters etc.. When engine reaches optimal temp of 90*C the volatge starts to drop to 13 and if turns cosumers like lights heaters the cars dies from loss of voltage.

We checked the alternator even we swap few same result. We even added aditional battery direcly to alternator to boost up the voltage but same thing.

the guy swapt his positive gable with new one and the installation of the car is brand new so it's unlikely to have any leaks.

Engine has only one ground cable - the one from back side of the head. Is it possible that he needs one more or maybe thicker positive cable?

[quattro swb]

hi there he needs a negative <earth cable> from the battery to the body as the engine/gearbox is rubber mounted as such so it will have a poor condutivity.....................shaun

[Nik0las]

Hi,

He does have a negative cable from battery to the body, from head to the body only missing bottom one from engine mounts to the geaebox or to the body - could this be the problem

[John.]

With the engine running and consumers switched on, use a volt-meter to check for volts drop;- go between the battery positive terminal and alternator output, the reading should be very low(like 0.1v), if it's reading for example 3.5v then you have high resistance on this part of the circuit. Moving the volt-meter probes around different points you should be able to pinpoint where the fault lies. The same can be done on the earth circuit.
Most automotive multi-meters explain these sort of tests in the instruction book.....probably better than what I can!!
Or what about attaching the volt-meter to the battery terminals and use a jump lead as a temporary earth lead, connect between various points and when the voltage improves then here lies the problem area ?
Good luck .
John.

Does it only do this at idle speed? If you keep the revs up is it ok?..... if so alternator suspect.

[Nik0las]

Yes when you keep the revs UP is OK...

[John.]

When engine reaches optimal temp of 90*C the volatge starts to drop to 13 and if turns cosumers like lights heaters the cars dies from loss of voltage.

How soon after the consumers are switched on does the engine die? Does the engine restart again ok?
Is it possible you have an idle/air fault?
J.
What car is this on?!

[Nik0las]

No it's electrical issue not related to air fault - this happens only when car is in optimal operational temp arround 90*C. As much consumers you switch on that much voltage drops and this of course reflects the idle and engine dies. If you keep certain revs everything is ok but voltage is still bellow 13.5v.