I have a 92 park ave that has several problems. First, most of the time I have trouble getting it out of park. I usually have to tap the throttle, mash the brake pedal immidiately and jerk the column shifter. Works most of the time. Second, I have some sort of vacuum problem, I think. When I have the A/C on in the summer, it works ok until I accellerate hard or pull a hill, then it switches from the vents to defrost. Same thing with the heater, will always switch to defrost under a load. A year ago, I found a small leak in the square vacuum box on the firewall, so I sealed it and it seemed to work fine last summer. This summer I had the problem again, so I super glued the whole seam, but it didn't help the problem. I replaced all rubber sections of vacuum lines at the ends of the metal lines, and looked for leaks in the engine compartment, couldn't find any. And when winter hit, defrost only now. Sound like a vacuum problem?? Third, the car never heats up to temp in the winter, not very warm air and temp guage shows cold. I have the entire radiator covered and it helps a little, but not much. I replaced the temp sending unit a year ago, and the thermostat 3 times in 3 years. ok, any help will be appreciated, thanks in advance

I am sooo disappointed no one here could help

dont really know your car but it does sound like a vacuum issue, you should take the control unit out and see if theres anything obvious there. another trick is to spray brake or carb cleaner around the line ends and see if the engine changes pitch

Regarding the lack of heat in the winter, I hate to say, but it looks like you are due for thermostat #4. The only other possibility is that there is no o-ring on the thermostat, but that means it was not put on with one. Either case, you may as well just replace the thermostat again.

Coming out of park: if you try pulling the shifter out of park with the ignition unlocked, but not on (first click, no power to radio, dash, etc) do you still have the problem? Do you park on a hill? Does it help if you rock the vehicle back and forth without revving to come out?

The vent issue, it sounds like there is a vacuum leak, somewhere. Have you looked in to simply replacing the vacuum reservoir? Probably would be a good idea to replace all of the vacuum lines, they would be coming up on 20 years old after all.

the t-stat does have the rubber seal on it. If I replaced it 3 times with no improvement, why would you suggest I do it a 4th?

Because it was my understanding that the problem would be resolved, and then return. Reviewing your post, I find that assessment to be mistaken.

Now, I am proceeding under the assumption that the vehicle is not actually coming up to temperature. The thermostat controls how cold the engine can run. As long as it has a proper seal, there should be no coolant going through it. I will run down the possibilities, and you pick which ones may apply.

O-Ring not properly installed/seated, allowing coolant to flow right past the sides of the thermostat. You indicated it was properly installed each time, that'* great.

Wrong thermostat. You know, wrong size, for the wrong engine, etc. I hope this is not the case as you have replaced it twice so far.

The thermostat is locked open. Many advertise Fail Safes, which lock open if the thermostat opens wide enough. Could also simply be stuck, etc.

One scenario comes to mind. You install Fail Safe thermostat. You start engine and let it come to temp, only to have a giant air pocket behind the thermostat. The engine becomes raging hot, and you have no indication. The thermostat finally opens, and releases the air pocket, and the raging hot coolant hits the thermostat, and trips the Fail Safe. You have now just killed a brand new thermostat on your first start, it stays open, and you continue to curse the car.

Something else that was mentioned to me elsewhere, was thermostat orientation. You sure you didn't put it in upside down?

One thing I would be inclined to do is check the running temp of the car using an external means. I use an infrared thermometer on the thermostat housing. This confirms the car is actually running cold. If it is coming up to temp properly, you may want to check the temp sender unit (I believe there is two, but am not sure), the dash gauge, and for your lack of heat, the air mix actuator (a common failure point actually).

Others like to check the thermostat operation by sticking it in a pot of water on the stove, and checking what temp it opens up, as compared to what it should be.