1993 Cadillac Seville STS Northstar Overheat w AC and No Heat?

Posted by admin on Dec 25th

I’d REALLY appreciate some insight to a problem Ive been having with a car I just bought. Its a 1993 Caddy STS with a Northstar 4.6 V8. I bought the car yesterday (For a steal I thought 1500!) it has 99K original miles and excellent service records.
However, When I bought the car it was about 85 degrees outside. So, when I tested the heat in the car (very important when buying any used car) just room temp air blew out. The owners neighbor (who was in charge of handling sales while he was on vacation) said it was probably not blowing out “hot heat” because of the climate control system.
So, this morning it was around 70 here and i put the car inside temp to 90 degrees. Still NO HEAT.
Also, nothings coming from the vents just blowing from the dash and doors onto side windows.
Here is part 2….. the car is running around 220-245 when driving down the highway according to the computer. Is this normal? Because when I put the A/C on (which does work well) It will cause the computer to say “Engine Hot” and it turns the a/c compressor off. I turn off the a/c and it goes back down to the 230-40ish range and drives fine. There are no error messages other than a suspention message which I believe may be a bad strut on the passengers side. There is No white smoke from exaust. No water or gas in oil. No sign of gas in coolant etc.. the motor is very quiet and purrs.
Ugh…..Im so upset! My last car didnt have heat ALL winter and I swore I would never buy a car that didnt!!!!! Me and the kids FROZE! I finally got rid of that other pc o crap from last winter (that at least the a/c worked in summer) Now I cant even use the A/C in this car in fear I will overheat the engine. No Heat. Cant use A/C. And Im all out of Money!! I would really, really appreciate anyones help.
when i said running around 230-240 on the highway I meant the coolant temp…lol not speed…just thought Id mention that!

Filed Under: Water for Gas FAQ
Tagged: 1993, Cadillac, Heat, Northstar, Overheat, Seville

4 Responses to “1993 Cadillac Seville STS Northstar Overheat w AC and No Heat?”

Dec 25th at 12:20 am By: Crazydave

NOTE… The heat and AC are both controled by the climent control system you could have a bad control panel.very comon. Have it checked first before changing it.

Dec 25th at 1:07 am By: Edwin

220 degrees is usually tops for engine temperature. Anything above this is considered running hot. I recommend you run the engine and check to see that your fan is kicking on. If it is kicking on check the temperature and see how far in the hot before it kicks on. Most thermostats open at 182 degrees at the most I’ve seen thermostats that open at 192 degrees. So you might have a defective thermostat. When you turn the A/C on the fan should go into high speed if equipped with on fan or with a two fan system both fans should be on. You might also have a faulty sending unit giving the wrong reading.

As far as the heat inside your vehicle, it sounds like either your blend door is not opening properly or the valve that permits hot coolant to go into the heater core could be stuck shut. For this you might want to contact a shop since this might be a little more than you’d want to deal with at home.

Dec 25th at 1:14 am By: Old guy_64...

Check your coolant level ice COLD..don’t go by the plastic jug level, it means nothing if the rad pressure cap is bad, because the rad level could still be low. Get the rad cap changed or buy a new one for ten bucks it’s worth the money. Hot temperatures could also cause A/C mis ups on the computer in car, so don’t go nuts there until you check the basics god luck

Dec 25th at 1:28 am By: anthentherwasi

it could be a bad heater control valve or thermostat, but it could still be the head gasket failing that motor is known for it i have had at least 1 cadillac from 77-99 and never wanted the northstar engine

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1993 Cadillac Seville STS Northstar Overheat w AC and No Heat?