Heat not working properly

Disconnect the heater hoses and flush the heater core. Be very careful removing the heater hoses to prevent damage to the core by excessive flexing of the inlet & outlet tubes. You may have to cut the old hose off to get it off.

Next inspect the heater controls to make sure the air temp flapper isn't stuck so that it sources air from the A/C-vent side. Check the vacuum lines to make sure none of them are cracked or broken.

Note that both the images are reduced size. Clicking inside them after they are opened will give you the option of enlarging them.

The diagrams are for an 89 Mustang, but shold be similar for 87-93 model years. It is a good idea to use the sig under the user control panel (User CP) option. It allows you to post your car year & mods, which help greatly when troubleshooting things. No, it is not there for us to snoop and see any "Secrets" you have hidden away under the hood. Be a good stangnetter and update you sig for future reference & don't keep us guessing.

savegoodautonfg said:

my car temp guage seems to stay very low but my car runs fine except my heat never really gets hot and i have the thing on high. it doesnt want to get hot. sometimes its gets warm but doesnt seem to stay warm. something is definetly wrong. any suggestions?

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Is your thermostat in working order? When was it last replaced? When some of them fail, they have a "safe mode" of partially open at all times.

flushing would be the best idea. air pockets have a tendency to not allow the car to reach its full heating potential.

4u2nv said:

Is your thermostat in working order? When was it last replaced? When some of them fail, they have a "safe mode" of partially open at all times.

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This is the very 1st thing I would do as it is the likely culprit. And it's cheap too. If it still doesn't get warm, do the heater flush thing.

savegoodautonfg said:

Would do i get the stuff to flush the system and how?

I am only 17 years old and I dont know much about theses cars yet im still learning.

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Your local parts store will have flush-n-fill kits from reputable manufacturers.

You're fine! Everyone was "new" once.

While flushing the heater core or even replacing it if possible isnt a bad idea at all, this is definitely the thermostat. Its stuck open which doesnt allow the coolant to get to the right temp which keeps the guage low and the heat low because its always circulating through the radiator.

The local auto parts store will sell you a flush kit with instructions and the flush chemicals. The flush kit is about $5-$7, the flush chemicals are about the same. This will flush the whole cooling system, which is a good idea.

Carefully look the cooling system over for swollen or deteriorated hoses, rusted clamps or obvious leaks. Write it down so when you make the trip to the auto parts store you get everything you need in one trip.

Plan on spending some $ for 2 gallons of new antifreeze. Get the full strength stuff, buy the mix and you are paying $$$ for water. Mix it 50% antifreeze and 50% water and you will be good. The Chilton's shop manual says the cooling system holds 14 qts, so that's 3 1/2 gallons of mixed antifreeze if you have a dry system.

What typically happens is that there is clear water left in the system after you flush it. That means you need to add 7 qts of pure antifreeze (not antifreeze mix) to the radiator. I recommend that you remove the bottom hose from the radiator and drain the water from it. Reconnect the hose and then add the 7 qts of antifreeze, it may not all fit. Once the engine gets warm, the coolant level will drop, so add the rest of the 7 qts of antifreeze and more water to top it off. Check the coolant level after you have run the engine for 30 minutes or so. This will get all the air out of the system and allow you to top off the system with water.

Don't forget to empty and refill the overflow tank with the 50/50 mix to the proper mark. It holds the extra coolant that heat forces out of the radiator. When it cools off, the vacuum inside the radiator sucks it back in. After a while, everything balances out, and the radiator has the right amount of coolant and the overflow has the right amount of excess coolant.

You probably will have some antifreeze mix left over, just keep it away from cats and dogs. It is poisonous and animals will drink it like soda pop. Killing your favorite pet (or your neighbors) isn’t a good thing. This means you need to thoroughly wash down your work area when you finish to clean up all the traces of antifreeze.

A new thermostat is a good idea, but the lower thermostat bolt can be hard to get to. Make sure you have the tools to get to it before you purchase a thermostat. I have a 1/4" drive, shallow 1/2" universal socket and it is the only tool that makes the job easy. If you change the thermostat, you will need some blue silicone sealer for the gasket area.

Plan on spending $20 or so on a Chilton's shop manual. It is the best tool investment you can spend on a Mustang. You may not be able to do everything, but you can do a lot of the work yourself and save major $$$.

Sounds like a clogged heater core. I just had this happen a couple weeks ago on my daily beater. If not the heater core, the thermostat.

jrichker said:

It holds the extra coolant that heat forces out of the radiator. When it cools off, the vacuum inside the radiator sucks it back in. .

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Joe, my system still won't suck back the coolant from the overflow. I let it sit for 3 days, and I lost about 1/2 gal. coolant through that leak developed from the broken water pump bolt.
Could that leak also be de-pressuriaing the system and prohibiting the system from sucking the overflow back in?
The overflow was still between hot and cold full, but I was 1/2 gal. low in the rad.
I don't get it...