Please help! car overheating

Maintenance/Repairs
1

Ok I’m new so I apologize ahead of time for mistakes.

The problem I’m having is with a 1994 mercury sable 3.8

Let me start off with the things I’ve fixed, water pump, thermostat, radiator, complete head job done profesionally, and fan is straight wired to run on high all the time.

Now the interesting part. The car immediately overheard when the AC is turned on and only when it’s on. It only overheats when your moving, not when your in park or in stopped traffic. What the heck is going on with it? All fluids are changed regularly and full. i unplugged the temp gauge sensor when running and it did not drop the needle does this mean it’s bad?

2

complete head jobonally done,

What is this ???

Yosemite

3

I fixed the typo ok got any advice on the car…

4

Confirm “complete head job” means new head gaskets.

5

New gaskets, shaved head, the works.

6

Is it really overheating, or only that the gauge says it is?

7

The gauge is my only insight on the overheating. It hadn’t driven different. But I’m not sure.

8

How do I tell if it is overheating other than the gauge

9

The mechanic you used should be able to measure the heat of the coolant. I think, but don’t know for certain, that the gauge should go to cold when unplugged. There has got to be a way to measure the actual temperature of the coolant, regardless of the reading on the gauge.

10

It just continued to read high when unplugged, my gauge doesn’t have degrees, it says
N O R M A L. Spread across the gauge, and when it acts up is well above O and sometimes above N.
Buy when unplugged just stays that way like it’s still working. When I turn the A/C off it takes 31 seconds to go back to M which is where it should be for when it’s warmed up.

11

Sounds like a faulty gauge or possibly a bad thermostat. New ones can be bad too.

12

If it’s not the thermostat, and not the gauge is there anything else that is possibly the cause of it?

13

It’s been a long day and I’m tired, but if the needle is on the N or O, wouldn’t that be cold?

14

Yup. I noticed the same thing.
OP, are you sure you’re interpreting the gage correctly? Can you post a photo of the gage when the needle is in the area that’s causing you concern?

15

Are you sure your radiator fans are turning the right way, that is pulling air in through the rad and not pushing it out the front?

16

Picture at bottom right of this link is the gauge

17

Also, are you sure you disconnected it from the correct temp sensor. If you have a guage there should be one for the guage and one for the engine. I’m getting beyond my competence level but I think the computer will read the engine temp sensor so you can see if it really is over heating or use the infrared gun on the radiator/engine. Sure sounds like an electrical issue instead of a cooling issue though from the weird symptoms.

18

When the needle hits N or O on NORMAL it’s hot. The link shows the gauge

19

As far as I know there is only one on the sable. And it’s mounted directly on the thermostat housing.

20

Are you sure? I don’t see N O R M A L on that gage. OOPS! I see it now. I had to zoom the photo.

The N and the O are within the normal range still. And it would not be unusual for an engine to run warmer with the A/C on. The compressor places a lot of load on the crankshaft.