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SuperRallyRoo

Overheating when headlights are on.

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On my 1981 hatchback it overheats when I turn the headlights on, like goes right under the red and I am pretty sure its telling the truth because if i'm on the freeway I can barely maintain what it says is 50mph (27" tires) and it starts top sputter and cough. So I turn the headlights off on the freeway at 12 night, and just drive cause my tail lights are hardwired to the acc. So Anyway it cools down after I turn the lights off. The heater on full blast on hot seems to do nothing. But it also doesn't seem that hot! So I really have no idea whats going on. At first the radiator was a little low, but that didn't help when i put some water in it. Should I try to dump some more anti freeze in there, change the radiator, change the thermostat? Look at the head light wiring? I'm thinking about rewiring the headlights and seeing if that does the trick. Please help!

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Just taking a stab at this. How is the fan,water pump, alt belt. (Assuming it's all one belt.) Is it tight? If it's tight, is it riding low in the VEE pullies? Even if flat serpentine belt, they wear to the point that even though tight, they won't grab well onto VEEs of the pullies. When head lights are off, this belt has to transfer less horse power to the accys it's driving and may turn the fan and water pump better with what HP those need. Adding the extra HP the altinator requires to keep up with the lights being on, may cause it to slip more. Do you have a volt gage on the dash? If so, is it dropping bout the same time the temps going up?

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My friend Fabio who knows his wiring shizit... Found the problems. It was 2 major voltage drops 1 at the headlights itself where someone (previous owner maybe?) cut the headlight low beam wire and crimped it togethor by hand! So we fixed that, there was alot of bogus junk wiring held togethor by black duct tape that we soldered togethor and fixed... The battery terminals where cleaned, and we fixed the ground going to the engine and to the body. It actually idles smoother and does not have a 2 1/2 volt drop when the head lights are turned on! It doesn't overheat anymore either. So ya wooo hoo I'm happy now :) Sounds like I have a sticky lifter though because sometimes it just ticks like mad! I have full oil and magic marvel mystery oil... So i don't know what the problem is there. Anyway gonna go test drive it some more.

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I was having a simaliar problem with my 81 wagon, turns out that one of the fans doesn't come on when the lights are one.

 

Lights on = 1 fans

Lights off = 2 fans

 

give it a try when your car is hot, watch the fans and turn your lights on and off.

 

I guess the engineers thought they could get by with a weaker alt if they did this little trick.

 

Hope this helps

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ea81's only have one fan, just so ya know, unless they're equipped with a/c, then they'll have 2 fans, and I believe one of them will be permentally on.

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The secondary fan comes on only with the AC, (Both MIGHT kick in when the temp sensor turns teh main fan on, but I am not sure) however, the secondary fan only kicks on if the headlights are off. I had a similar problem with my 83, someone had wired the second fan in as the main one, to kick on with the temp sensor, however, they wired it to teh sub fan relay, so the secondary fan would only come on if the temperature rose AND the heater switch was in AC or defrost, and the headlights were off.

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that sounds interesting, if I ever get an a/c car, I'm modifying the secondary so the headlights have no effect on it's function:brow:

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