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Discussion Starter #1
Have a 95 Plymouth Voyager that only rarely has heat.
•will occasionally have heat for a minute or two.
•temperature gauge will warm up some then goes dead
•may be unrelated but factory stereo stopped working around the same time
•has new thermostat
•testing seems that if the temp gauge begins rising it has heat, gauge goes dead then pretty quickly the heat go cold.
○so could it be an issue with the temperature sensor at the thermostat ect? I cannot be sure what is electrically controlled and vehicle is not home right now although the heater control valve apears to be vacuum controlled.
Thoughts? With our current finances I cant blow money but cannot have small kids in a freezing van at 6am. Thank guys! Dave
 

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Welcome to Allpar. Does the upper radiator hose up front and heater hoses into the vehicle get warm to the touch?
The vacuum valve is only to close off the warm coolant in the Max A/C-recirc position. Otherwise it should allow coolant flow through the heater core year 'round.
Is the radiator cap holding pressure? Don't remove it on a hot engine, but squeeze the radiator hose to feel if it is under pressure when the engine is warm.
Does it have heat if it is sitting still and running, but loses heat shortly after driving away?
How is the health of the cooling system in general? No coolant leaks or coolant smells? If it is low, there may be a leak. Building and holding pressure when hot? Recent flush?
At 22 years old, has it ever had radiator/water pump/heater core replacement?
The heater core may be restricted and plugging with debris/corrosion. Sometimes a reverse-flush will clear debris if it is soft material.
The blend door in the dash is cable operated and should slide between cold and warm with the dash lever. Is it sliding freely and do you hear the door 'thunk' at one end of its travel?
I doubt that this is electrical. It sounds like when the temperature gauge drops to 'C' and you lose heat at the same time, that it is telling you the truth.
Did the thermostat replacement make any difference in temperature and was it installed correctly with an OEM part?
 

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I believe your temperature gauge going dead and not indicating true engine temperature is an electrical problem either at the sensor or in the instrument cluster. If the engine is running too cold and does not reach proper operating temperature a diagnostic code 17 will be set. Use the key dance (ON-OFF, ON-OFF, ON) and count the flashes of the CHECK ENGINE lamp.

Let the engine run 15 - 20 minutes. Feel the heater inlet and outlet hoses at the firewall. They should be hot to the touch. If the inlet is warm and the outlet cool or lukewarm or both are cool, then you have lack of circulation through the core. The heater inlet hose should originate at the intake manifold in the area near the transmission bell housing.

I have seen a partially plugged core provide heat for a short period of time and then go cold as corrosion breaks loose and blocks flow and heat transfer.
 

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Have a 95 Plymouth Voyager that only rarely has heat.
•will occasionally have heat for a minute or two.
•temperature gauge will warm up some then goes dead
•may be unrelated but factory stereo stopped working around the same time
•has new thermostat
•testing seems that if the temp gauge begins rising it has heat, gauge goes dead then pretty quickly the heat go cold.
○so could it be an issue with the temperature sensor at the thermostat ect? I cannot be sure what is electrically controlled and vehicle is not home right now although the heater control valve apears to be vacuum controlled.
Thoughts? With our current finances I cant blow money but cannot have small kids in a freezing van at 6am. Thank guys! Dave

Are you SURE the cooling system is completely full? Don't just rely on the overflow jug level - remove the radiator cap when the engine is cool and see if the radiator is also full. If not, fill it and check for leaks. I suspect you have air trapped in the system, due to low coolant.

If the coolant level is low, and it is not being drawn into the radiator from the coolant overflow jug, you may have a defective radiator cap.
 

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I 2nd 1999 White C5 Coupe's suggestion. If the coolant level is too low, coolant won't circulate through the heater core, and thus you will get no heat out of it. And before the thermostat opens, coolant is directed to the heater core, after the thermostat opens, coolant is directed to the heater core and Radiator. So getting a little heat before reaching full operating temp and then no heat is still perfectly consistent with low coolant level.

The overflow jug catches coolant forced out of the system when the coolant expands with temperature, after you shut down the engine, the coolant cools and contracts and forms a vacuum that sucks the coolant back in from the jug. If the cooling system is working perfectly (and your's is NOT) the overflow jug would indicate the relative coolant level. If you have a leak in the cooling system, not only would you be loosing coolant, after engine shutdown, the vacuum that forms as the coolant contracts would suck air in through the leak instead of sucking coolant back in from the overflow jug. So the level of the overflow jug can fool you with a poorly operating cooling system.

Your electrical issues "may" be unrelated to a cooling system leak, and the temp gauge going dead is probably an electrical issue.

It doesn't cost anything and can't hurt to check the coolant level under the cap, well unless of course you foolishly remove the pressure cap while the engine/coolant is hot, then you could get burned badly. Wait until the engine is cool before popping the pressure cap and see if the coolant level comes up to within an inch under the cap opening. If not, you need to add coolant.
 

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Discussion Starter #6
Thanks to everyone for the help. The hot air does seem to die after starting to drive a short distance after being warm at idle. I believe the water pump was in fact replaced at some point a few years ago. I will check heatercore hoses and coolant level in radiator and see how it looks and wether i need to top off and bleed the system.
 

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The water pump is a common item to develop leaks, if the water pump had been replaced with a rebuild or less than quality new water pump, starting to leak in a few years is a real possibility. The mini-vans are know for needing a new water pump from time to time, look to see if it is wet or dripping from the weep hole near the base of the shaft going into the pump.

But its too early to tell if you even have a leak. Check the coolant level under the pressure cap, only when the engine is cold, look the whole system over looking for signs of a leak. Remember, when the engine is at full operating temp, the cooling system will pressurize to 16 PSI or what ever pressure the pressure cap is rated for, you should squeeze the big hoses to the radiator and they should feel hard with pressure pushing from inside them. If those hoses are soft and flexible, easy to pinch in, then you definitely have a leak bad enough the cooling system is not holding pressure and that will result in loosing a significant amount of coolant.
 

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Also while squeezing the upper radiator hose can you hear any gurgling in the overflow container? Radiator cap could be bad.
On the 3 liter there is a pipe from the back of the water pump that goes the length of the engine under the intake manifold. This pipe is know to rust and the O rings on the ends of the pipe can leak.
 

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Buy, rent or borrow a cooling system pressure tester. See if the system holds pressure and if the cap holds pressure.
 
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Discussion Starter #10
Hey guys I FINALLY got some time off work where she has been home and then had to wait on the down pours to stop. Then of course that holiday my kids flipped out over lol. So I cannot find any leaks, a few 2 and 3 hour drives and it hasnt lost coolant. Heater only works when car is completely stopped and idling for awhile i.e. drive through. When it works its only warm certainly not hot. Hose to thermostat is getting hot. Hose into heater core gets a little hot but you can hold your fingers to it. Outlet barely warm. Heater control valve is functioning and opening up in driveway but cant tell once driving obviously. Once she starts driving the heat goes freezing cold very fast and temp gauge bottoms out.
 

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I'll ask what seems like a dumb question and don't be insulted, but was the thermostat installed in the correct direction, with the spring pointed toward the engine block/head? And is it the right temperature rating (usually 195F)?
 

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Discussion Starter #12
Yea. It was improperly installed once before by another person and i fixed it (gasket on wrong side so the thermostat wasnt sitting in groove and shifted over and leaked some)
 

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Discussion Starter #13
Oh and I made sure to get the oem spec part. *i wont say it didnt fail shortly after install though, it is a failsafe thermostat so it fails open not closed
 

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Can you hear the blend door "thunk" when moved from cold to hot or vice versa? I believe it is a cable driven system.

Sounds like a clogged heater core. I'd try a reverse flush using a garden hose (low pressure) or a chemical flush.
 

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I suspect your thermostat is stuck open.When you say the gauge goes dead, does it drop to the cold position when driving, and does it start to recover when idling? When moving, airflow through the radiator can remove so much heat from the coolant that the gauge will drop to full cold if the thermostat is not functioning properly to restrict coolant flow.
 

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Agree. The cooling off once the vehicle is in motion as opposed to it being parked means that coolant is flowing through the radiator when it should not be.
This will reduce good heater performance and is likely caused by a thermostat that is stuck partially or fully open. I have found things like a good and recently changed thermostat with the poppet valve hung open by an old piece of paper gasket shaving.
Of course if the thermostat has been recently changed, it won't be suspected as the problem again.
 

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Discussion Starter #17
Hey guys. Im definitely thinking of going ahead and changing thermostat again, and failing that, flushing heater coil. Its a cheap part and cant hurt to try.
 
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