I have a 95 voyager that does not maintain heat. It will get fairly warm when you start it and let it sit and warm up. Then when you go somewhere it starts cooling down and blows cold air.I checked the top radiator hose and seems close to 190 degrees. I checked the vacuum fittings and all the lines and didn't notice any leaks and there was vacuum pressure.I tried covering the front grill with cardboard and this didn't have any effect.I'm thinking either thermostat or heater coil ? Also is there a website that anyone knows of that has free auto/van repair guides that are illustrated? Thank you for any info Scott

Well when it starts blowing cold air, is that when your driving or is that when you turn off the engine?

It slowly turns cold while your driving it, but when you stop and leave it running it still won't warm up. It only gets warm when you start it the first time, almost as if it doesn't have enough of something to keep the temp up.The radiator is full.

Replace the thermostat and radiator cap.

I can see changing the thermostat, but why the radiator cap? It seems to be fine, no leaks.Just curious. Thank you for your opinion.

Scott,
If the radiator cap has lost spring tension that would cause system pressure to escape
Into the overflow or steam out through the cap. If your coolant level remains full then it is
Likely good. The system needs to be sealed tight to work effectively.
Buy a HAYNES repair manual at the parts store for around $ 16 it will guide you with
Info & pictures on almost everything for your van.
Also check the temperature of the hoses going in and out of the heater core that they
Are hot ensuring good flow through the core.

This site might help you a bit too: http://www.misterfixit.com/

Ok,Ive changed the thermostat and the cap is sealing just fine and it seems to have done nothing to change the temp. On a warm day the heat seems to work,and on cold days it starts warm and then quickly gets colder when you start moving and doesn't get warm again until you shut it off and let it sit for awhile.Thanks again.