Ok so I bought this 99 Grand Marquis used I love it to death it runs great..except that my heat just went out right before I had to change the plastic intake manifold out. Below is a list of things i've done and checked to give you an idea of maybe what it could be.

I have replaced the Intake manifold so now there isn't a plastic thermostat housing.

I have flushed my radiator and heater core. Both of which are solid and have no leaks. (When I flushed them no gunk really came out either just dirty coolant and then clear water).

My vacuum switch seems to be working underneath my heater core completely fine.

There is a new thermostat in there as well.

The one thing I noticed that seems to be apart of the issue .. is if you are standing in front of the car looking down at the engine. The hose going from the radiator to the thermostat housing and the hose going from bottom right of the radiator to the engine block(maybe waterpump?) are not full will coolant. I can easily pinch both sides of those two hoses. They are getting flow through them but severely restricted flow it seems.

I know I should be getting way more flow through the tubes but what else could be clogged? Do water pumps get clogged or right inside the engine block?

Any suggestions are greatly appreciated as well as any questions or pictures you guys need to help me I can provide!

Thanks in advance and im excited to join the community,
Paul

 

A little update here..

So after a few days it seems the water flow/pressure is back in my hoses way more than before..seems like something blew through.

But still no heat.

So I guess another question for you guys would be, can a heater core go bad and not leak or give off antifreeze smell?

 

Well, heater cores can easily clog, but are you sure you are getting good coolant flow?

Are both sides of the heater hoses (input and output) hot? If not, then I suspect a clogged heater core.

Some people have used CLR and poured it into the core's input and let it sit overnight to clear clogs.

Let us know how you make out, Bill

 

Okay I have fixed my heat a few days ago and its really dumb what it was..

I had to try and replace everything else along the way to even figure it out haha..

It was the blend door actuator switch if anyone is not sure what that is I can post a picture of it.

It is an 8 or 10 pin electric connection on the top of it.. and if you have a Bench power supply with 12v/5v +/- rails you can test them but I do not..

For this power supply im talking about you can turn a ATX computer power supply into a bench power supply and be able to bench test many many electric things for your car. Following is a tutorial on building one.

http://jumperone.com/2011/06/atx-power-supply-tutorial/