Cadillac Owners Forum banner

1 - 12 of 12 Posts

·
Registered
2010 CTS (Elvis) 1964 Impala (Betty) 1991 Miata (Dolly)
Joined
·
14,333 Posts
Discussion Starter #1
I'm getting very little heat in my '91 DeVille. Even though I have the temperature set to 90º, the air coming out is barely warm. The blower is working fine, and if I put it on defog/defrost, the air comes out the defroster vents.

I flushed the cooling system over the weekend, put in new coolant and replaced the radiator cap and thermostat (195º). All three hoses from the T fitting are warm to the touch after driving, so I don't think the T fitting is clogged.

The only thing left that I can think of is the heater core. I had hoped that flushing the cooling system would clear out any blockage. I drove the car for about 20 minutes with the flush in it, then another 20 minutes with plain water to rinse out the flush. I had the heater going with the temperature set at 90º the whole time.

So what do you guys think? Bad heater core? Or could it be something else?
 

·
Registered
Joined
·
40 Posts
Before jumping the gun on the heater core, I would remove the thermostat and place it in a pan of water on the stove with a cooking thermometer in the water, heat it up and make sure the t-stat is working properly. Sometimes even new ones don't work right.
 

·
Super Moderator
White Diamond '03 DHS (with DTS floor shift)
Joined
·
86,781 Posts
Did you replace the "T" fitting? It is supposed to have a restrictor in it. If you replaced it with a generic one without the "T", it will not heat properly.
 

·
Registered
2010 CTS (Elvis) 1964 Impala (Betty) 1991 Miata (Dolly)
Joined
·
14,333 Posts
Discussion Starter #4
I have not replaced the T fitting. All three hoses that plug into the T fitting are hot after I've driven the car.

If I need to replace the T fitting, is this something that I need to buy from the dealer? Do you know the part number? Or can I buy at NAPA so long as it has the restrictor?
 

·
Super Moderator
White Diamond '03 DHS (with DTS floor shift)
Joined
·
86,781 Posts
Just so long as it has the restrictor, or you make one. Not sure if Napa has it or not, but if you did not remove it, then it is must still be there. Perhaps an air mix door hanging up. Try running the temp to max and min several time to see if thet frees anything up.
 

·
Registered
2010 CTS (Elvis) 1964 Impala (Betty) 1991 Miata (Dolly)
Joined
·
14,333 Posts
Discussion Starter #6
Thanks for the advice Ranger.

Driving home this evening, I had reasonably warm air coming out of the right side of the defroster vents; the left side and rear seat vents had cool air. It didn't seem to matter if I had the temperature set at 90º or 75º. If I put the system on Econ, just cool air came out from the floor vent.

I'm going to try replacing the T and flushing the heater core, possibly tomorrow.

BTW, the past two days when I've gotten in my car after work, the windshield is all fogged up. None of the other windows are. The car is parked facing north, and according to the Weather Channel Web site, the temperature is 37º, the humidity is 91%, and the dew point is 35º. If my heater core is leaking, would that moisture cause my windshield to fog up? I can also smell a little bit of anti-freeze, but I don't know if that smell is leftover from flushing the cooling system.
 

·
Super Moderator
White Diamond '03 DHS (with DTS floor shift)
Joined
·
86,781 Posts
A leaking heater core definately will cause the windows to fog up and produce a coolant smell in the car. Rub your finger on the fogged windshield. Is it oily? Is the carpet damp on the passenger side? It may not be if the leak is small as the coolant will just evaporate and enter the cabin as vapor rather than a drip.
 

·
Registered
Joined
·
17 Posts
The heater core in the 91 is famous for plugging up. I hope it isn't your problem but if it is, search this site for helpful directions on how to remove the core. I have found some quite detailed step by step with photos here. Wish I could tell you exactly where. Not an easy job but possible. Good luck in finding the problem. My 91 has the same problem but in Phoenix I rarely need the heater.
 

·
Registered
88 Sedan Deville, 89 Eldorado, 11 SRX, 18 CT6
Joined
·
130 Posts
there is also a hose that goes from the core back to the heater pump. usually if you look, the heater core does not care the position of the thermostat because it goes through the T's prior to Tstat. Tstat controlls flow to radiator. on my 90 fleetwood, the hose that came from the core back to the pump was clogged with crud, changed that one hose (4 bucks) and all is well again. hope it helps.... also, the Valve to the core the lil metal type thingy on the top back of engine area,,, see if that opens and closes as you set from (in econ) 60 to 90. if it dont, you may wanna change that as well. also if theres even a drop of antifreeze in the hole the metal valve goes through, replace.
 

·
Registered
2010 CTS (Elvis) 1964 Impala (Betty) 1991 Miata (Dolly)
Joined
·
14,333 Posts
Discussion Starter #11
I was doing some other work on the car this weekend, so I tried flushing the heater core without much success (I think I got more water in the engine bay than anywhere else). Replace the heater control valve since ends from the old one broke when taking the hoses off. Can't believe I had to pay $16.99 for a piece of plastic that probably costs 50 cents to make. But it does have the restriction on the line going to the heater core.

Anyway, I still have weak heat, except for the passenger side defroster vents. So I'm planning to replace the heater unless there's something I missed.
 

·
Registered
94 Fleetwood Brougham
Joined
·
7,534 Posts
Does the T have the restriction in it? If not, the coolant will bypass the core causing low temps. Verify thermostat operation on the diagnostic, no need for a pan to boil it in. P.0.4 is coolant temp. Look for 90C or higher while driving. A slight temp boost may be found by plugging the line that goes down out of the T (this is the bypass) Noise and core eroision are rumors to why the bypass exists. Reversing the hoses may help, IF you can get to them.

If that all is ok. Heater core likely needs to be flushed. You will note that more heat is common the pass side of the car than driver's side. Again, sign of the core getting plugged.

http://www.cadillacforums.com/forums/showthread.php?t=33642

I came up with a way that you can flush the core w/o getting to the hoses at the core itself (on a 91-up that is nearly impossible).

Easy and enjoy the heat!!

Tom


gdwriter said:
I was doing some other work on the car this weekend, so I tried flushing the heater core without much success (I think I got more water in the engine bay than anywhere else). Replace the heater control valve since ends from the old one broke when taking the hoses off. Can't believe I had to pay $16.99 for a piece of plastic that probably costs 50 cents to make. But it does have the restriction on the line going to the heater core.

Anyway, I still have weak heat, except for the passenger side defroster vents. So I'm planning to replace the heater unless there's something I missed.
 
1 - 12 of 12 Posts
Top