[washingtonkevin]

1994 Mustang temp guage says hot but blowing cold air. Help please.


Here is the situation
1994 V6 Mustang with 140,000 miles.

Here is the symptom. The problem is intermittent for the last few weeks.

Temperature guage goes to the red line while blowing cold air from the dashboard vents. (Heater is set to hot on dash)
Then, it will start blowing hot air and guage will come back down to the N or O in Normal.

The thermostat has been replaced and I had the coolant flushed at a shop this morning. (It was due an oil change so I had them do it)
The oil and coolant show no signs of mixing.

The temp sensor and the fan relay (ccrm module) and the fan are all working normally.

What is the problem? Radiator blocked? (I would thought that would have showed up at the shop this morning during the flush)

Which hoses to/from the radiator should have pressure in them when I grab them? Can a hose delaminate on the inside and create a blockage?

I would like to figure out what is wrong with this without just throwing money away that does not need to be. Any ideas would be appreciated.

Kevin

[EagleAutosports]

Your hoses will deteriorate from the inside, yes. I would think it's possible to cause a blockage that way but I'd check the water pump, especially if it's got 140K miles on it.

[kscoyote]

Water pump, thermostat (always fails when you install a new water pump, anyway) are number one.

head gasket #2.

radiator/hose failure #3.

[GT-EATER]

Check the thermostat forst its the cheapest fix , and I have seen them act like that before as well.

[bsintzel]

You said you replaced the thermostat, but you 'may' still have a problem there. The fact that you get heat at all is a good thing. What's better, is that the temperature gauge shows hot then goes back down when she starts blowing cold air. This tells me that the thermostat is cycling. To confirm if the thermostat is still the problem, try the following.

1 - Make sure your coolant level is topped up.
2 - Let her cool down.
3 - Take the rad cap off, start her up and place a newspaper in front of the radiator.
4 - Take a look in the rad filler and try to see if the coolant is moving around. It shouldn't be at this point as the thermostat should be closed. If it is, something is holding the thermostat diaphram open. It could be crud caught between the diaphram and the housing, or a bad bimetalic spring in the thermostat housing.

5 - Nowlet her get hot...but NOT too hot and remove the newspaper
6 - When gets up to what should be the operating temperature, take a peek inside the rad filler again and see if the coolant is moving around. If so, you know the thermostat is 'at least' opening and your water pump is doing its job. NOTE: DO NOT turn the engine off without first replacing the rad cap or it will boil over.
7 - Now take a look at the gauge and see if it's reading hot. If not, It would likely be the temperature sending unit or the connection to the gauge itself.
Another possibility, although less common, is an air lock in the cooling system. A large bubble will cause the sensor to alternate from hot to cool and cause the thermostat to close suddenly.

Let me know how it works out

[shinerstang]

I'm wondering if it was bled properly.....

[stangfreak12243]

Originally Posted by GT-EATER

Check the thermostat forst its the cheapest fix , and I have seen them act like that before as well.

Yea, try the thermostat first, some thermostats just act wierd for no apparent reason. Then I'd look into the water pump since you have 140,000 miles

[bsintzel]

About the bleeding thing. If they just opened the drain c.o.c.k (they bleeped me...lol) on the rad and nothing more, you may have an air bubble in the block. Because the thermostat is part of a 'closed loop' cooling system, it has to be removed (or open) prior to flushing it. Taking the top and bottom hoses off the block (with the thermostat still installed) can prevent the block from completely emptying out if the pin hole in the thermostat diaphram is plugged.

Like I suggested earlier, if you can see the coolant moving around in the rad when she's hot, the thermostat is open (this is a good sign). However...if you can see the coolant moving around in the rad when she's cold, the thermostat is 'stuck open' and this is definately 'not' a good sign. You shouldn't see coolant moving around in the rad filler tube when she's cold. BUT hey, there's an up-side to this -- fluid movement at all means the water pump is 'pumping'

Give it a check...it costs nuth'n. Get back to me.

GT-Eater...feel free to jump in if I've missed anything

[GT-EATER]

Just fill her up like you said and wait till she gets hot and see if there is movement across the radiator and the bleed it a couple of time it should be good to go .

[kscoyote]

Originally Posted by bsintzel

About the bleeding thing. If they just opened the drain c.o.c.k (they bleeped me...lol) on the rad and nothing more, you may have an air bubble in the block. Because the thermostat is part of a 'closed loop' cooling system, it has to be removed (or open) prior to flushing it. Taking the top and bottom hoses off the block (with the thermostat still installed) can prevent the block from completely emptying out if the pin hole in the thermostat diaphram is plugged.

Like I suggested earlier, if you can see the coolant moving around in the rad when she's hot, the thermostat is open (this is a good sign). However...if you can see the coolant moving around in the rad when she's cold, the thermostat is 'stuck open' and this is definately 'not' a good sign. You shouldn't see coolant moving around in the rad filler tube when she's cold. BUT hey, there's an up-side to this -- fluid movement at all means the water pump is 'pumping'

Give it a check...it costs nuth'n. Get back to me.

GT-Eater...feel free to jump in if I've missed anything

I picked up a stant radiator cap with a release valve.

When you hit an air bubble after refilling the radiator, you pull up on the lever -pshhhht! and the air bubble's gone.

Pretty trick!

[GT-EATER]

Originally Posted by kscoyote

I picked up a stant radiator cap with a release valve.

When you hit an air bubble after refilling the radiator, you pull up on the lever -pshhhht! and the air bubble's gone.

Pretty trick!

Yeah thats pretty sweet KS