When I drive at night with the lights on, my car runs hotter. But during the day it is fine. Any ideas?

Cheers,
heb.

 

Wild *** Guess, airflow/drag. The headlights either change how air flows into the rad or them sticking up requires the car to work just a bit harder to get the air moving.

How much hotter does it run?

 

actually, i had the same problem on my 81. i couldnt figure out what caused it but i am positive it never overheated. i just ran it and ignored it. if it doesnt overheat with the lights off, you may want to install an aftermarket temp gague.

 

With your lights on at night, this places additional load on the electrical system that is usually overcome by the alternator. Additional draw on the Alt is also going to increase drag on the belt that powers the Alt, possibly leading to lower engine rpm and also possibly causing a slightly higher engine temperature.

Some confounding variables are that at night, the air temperatures are normally a lot lower, which should aid cooling quite a bit. What you may have going on is that your clutch fan is getting close to going out, and with the additional load on the pulley system from the headlights being on, the fan isn't turning fast enough to draw air through the radiator and cool it efficiently.

This is a long-shot, but the symptoms that you describe are pretty strange to begin with.

Airflow around the front end would be very unlikely to cause this, since I've run ribbon tape along the front end at speed (under video) to observer airflow and the headlight lids being up do direct airflow OVER the car, instead of to the sides of the car, but this is on TOP, not in front of the radiator. The front bumper isolates airflow from above and below the bumper, preventing any impact from the headlight lids being up.

 

all cooling aside, LongDuck, i think it is more of anelectrical issue to where when the light switch is in the on position, something causes the temp gague to ground out and max out. mine did this and it never overheated or came close for that matter. you seem to be very knowledgeable. perhaps you have more insight.

 

Mine is doing this as well. I've concluded it's the fan clutch.

I drove during the day with the lights off, and hit the button to raise the lights. Waited, no change in temperature.
Turn on the lights, temperature gradually rises past 1/2 way. Off it is around 1/3.

I can stop the fan spinning with my hand. Spins longer than the 1 1/2 turns I'm told it should. Not sure if this is supposed to be measured cold or hot, but I'm pretty sure I've done both.

Strange, because when I got the car, it had a 15lb radiator cap, and it was under 1/3 on the gauge. Switched to the proper 13lb, and it's run hotter since.

 

If the voltage is not being properly regulated, the electrical gauges will not have the proper reference voltage and will give spurious readings. I'd check the voltage with the lights on and off and see if there is a difference.

 

I believe the voltage on the in-dash meter drops when I turn the lights on. Shouldn't it?

 

the belt might be slipping when the alternator is under load(ie lights on)
do you still have the smog pump belt hooked up? if not you might need a double belt pulley to keep the waterpump from slipping

 

The voltage drops on the in-dash meter when I push the brakes, turn on the fan, the lights, basically anything electrical. It only drops a little for each thing. For instance, stopped at a light at night, with lights on, foot on the brake, it sits around 12 volts. It's around 13 volts when I'm driving with the lights on.

All my belts are new, and tighter than when I bought the car with the old belts.

Oddly enough, sometimes at night with the temp near 1/2 on the gauge, it'll drop down to 1/3 or so, where it normally is during the day.

 

next time you drive at night and your temp starts to climb turn your lights off and watch the gauge, if the temp drops emmediatly then climbs when you turn them back on, its electrical. look for a current draw, ck connections at temp sender, ck that alt. is putting out enough charge, voltage should never drop below 12.5 with lights or accessories on if regulator working properly.

 

lol, why at night?

 

Well, lets see, sun hot, moon not. lol
it was late, had a brain fart, anyway just simulate the circumstances

 

anyone come up with a solid answer, i'd like to hear the cause

 

Tried driving during the day with your lights on and see what happens?

 

I drive during the day with the lights on in the rain, does the same thing.

Recently I tried the fan stopping thing again. Appearantly I chickened out too long before, and the engine had cooled too much. Now when I do it, I can't stop the fan with the car warmed up. BTW- doesn't hurt if you can stop the fan; I couldn't stop the blades, and I could see them deflecting inward. That hurt ):

 

check grounds. it is a common problem.

do any other gauges read strange or lights flicker.

try adding a ground to the engine and 1 to a strut tower bolt....

 

All the returns for the affected circuits above go through ground path X-13 which according to the wiring diagram is on the left suspension tower and under the left dash. not much help.