SC wont heat up

Lycaon1349

Registered User
was having problems with the sc heating up, changed the thermostat(it was stuck wide open like i thought) but now it still wont heat up, after about 10 or 15 minutes it heats up to about the bottom of the "normal" range and stops there. any ideas? all air seems to be bled out of the system, and its not the temp sensor just reading wrong, because theres no hot air coming in through the vents when i have the defrost on high heat. help!
 
Did you lock the t-stat in when installing?

The cooling systems on these cars/engines can be difficult to air bleed. If you trust the gauge (connector tight?), make sure you've done due diligence and carefully bled the cooling system after draining/filling.

Used the air bleed stand-off tube behind the thermostat housing while filling. Take care to double-check...heat it up to open the t-stat, let it cool down and then repeat by checking the level in the radiator and letting air bleed out thru the stand-off while patiently filling.

Be sure the overflow tube that goes to the overflow tank isn't blocked. Be sure the radiator cap is healthy. Fill the overflow tank to the 'COLD FILL' level when the engine/coolant is stone cold.
 
Actually i was wondering about that, the manual did say something about locking in the t-stat, and when i went to install it there didn't seem to be anything against which to lock it... then again the old one wasn't really locked in either... now I'm thinking about it, was the thermostat supposed to mount flush to the housing or the block side? i stuck the gasket to the block then mounted the t-stat then installed the housing and the t-stat kept sliding down the RTV i was trying to use to get it to stick while i mounted the housing... might that be my problem? also about the vent, i think I've got it filled right to the bottom of the tube, the radiator is full right up to the cap, and the reservoir is at the proper level as well... not sure if the coolant is making it to the heater core though? whats the likely-hood that there's air all the way back there?
 
not sure if the coolant is making it to the heater core though?
Thats most likely the problem. If you don't have a leak under the thermostat housing, (you can just feel the bottom for coolant), then be sure you are using a thermostat WITHOUT the bleed hole+rivet :rolleyes:
I don't know a way to clean residue from the heater core. I've tried flushing and tried cleaner and seems that the only way to get heat is to replace it. :(
 
the one i installed did have the bleed hole:(, so now i gotta pull it apart again and try to find one without that hole? the one i took out didnt have it. i could probably just back flush the heatercore, not something im looking forward to but whatever i gotta do to get this thing on the road with the least amount of issues as possible:)
 
>whats the likely-hood that there's air all the way back there?

Stuff happens - I've never had to go this far, but sometimes it can help to run the car up on ramps, etc. so the the radiator is higher than the heater core when filling/bleeding. Might want to select the heater and crank up the fan while filling with the engine running so you can compare the heat in the radiator to the heater output as the engine heats up - this is all before things get so hot that the cap should be in place...

As mentioned, if you're comfortable with the general cooling system operation and you've been careful to bleed it, but the heater still runs cool, it might be time to replace the heater core - not an easy task.
 
just fyi

the one i installed did have the bleed hole:(, so now i gotta pull it apart again and try to find one without that hole? the one i took out didnt have it. i could probably just back flush the heatercore, not something im looking forward to but whatever i gotta do to get this thing on the road with the least amount of issues as possible:)
In my DD, my underheating problems were solved by using a non bleed hole thermostat. Just that small bit of constant flow was enough to keep the car from heating up on a cold day. I used a Stant Superstat from Pepboys; they were the only ones that carried it.
 
Alright I think I'm just going to shoot for a motorcraft non-bleed tstat from rockauto, hopefully that'll solve my issue
 
No it doesn't come on at all cause of the low temp, unless of course the hvac system is active to cool the condenser

Edit: just picked up a non-bleed tstat from carquest, hopefully I can get some time tomorrow to install it and see how it does
 
Last edited:
Just wondering. Some folks do the #14 wire mod to run the fan all the time and then wonder why their car never warms up :rolleyes:.

Fraser
 
ok, so the new thermostat is in, its heating up to just above where it was before, just slightly above the mark in the normal range. still not enough to give me heat, although i can tell that there is temperature transfer going on at the heater core, the coolant is just not getting hot enough... im confused. anyone have any other ideas? the thermostat is working, its just not letting the coolant get hot enough to be in the proper range
 
I believe all the thunderbirds I have ever owned stayed at about the N on the engine temperature gauge. I think everything is fine, if the system is bled enough to drive the car and it doesn't overheat, then you are fine. It may take a couple days for the system to purge its air-pockets through the reservoir. My bleeder is frozen, I have never used it. I would say you definitely have to see if you can free up sludge from the heater core or you'll need to replace it. If you can free it up, my guess is you'll find out your heat works better than you could ever remember.

Now for the important part: How To Check If The Core Is Not Getting Good Flow.

There is entrance and exit hose for the coolant to flow through on the heater core. Get the engine to operating temperature, coolant always flows through the core so you don't want the heater fan on at all for this test. Now, check the two hoses going to and from the core. If it is severely plugged you will be able to tell a big temperature difference that the entrance hose is very warm and the exit is not near as warm because there is not a lot of flow through it. That will save you the pain in the arse of pulling it apart and wasting your time if thats not the problem
 
ok, so the new thermostat is in, its heating up to just above where it was before, just slightly above the mark in the normal range. still not enough to give me heat
Most of the stock SCs (those using the normal 192-195 degree thermostats) will have the temp guage between the "N" and "O" letters when completely warmed up. If yours is close to that mark, then the thermostat is doing what its supposed to. You're not running a 160, are you?

If your heater core+lines are working properly, there is enough coolant heat with the temp guage between the "N" and the L white line to get hot air.

Keep the coolant in the overflow bottle at the correct level for a day or 2 and the air will purge itself. Provided your radiator cap is working correctly. Then see if things improve. Its also a good idea to clean/tighten the connector on the temp sender on the thermostat housing, to be sure you're getting a solid temp reading.
 
Last edited:
yeah its running close to that, and no im not using a 160, im going to try to let it work itself out for a few days
 
Back
Top