No heat and thermostat light just came on. What's wrong?

Are you saying temp light came on? Check radiator coolant, and if low use instructions to refill. if coolant is ok, check if hose going from top of radiator to motor is warm after running for five or ten minutes. if not shut motor off and dont drive it. You probably need to change the thermostate where the hose goes to motor. if you continue driving you may blow a headgasket. A thermostat is an easy replacement. Two bolts. just make sure you place it right side up.

Low coolant level would create a low/no heat condition.Operating temperature would be affected by a stuck open thermostat along with coolant passing through the heater core where the heater obtains its "heat".

1-your thermostate is stuck open half way. thermostate is a simple device that made of enlarging metals when heat is applied. it suposed to be in close position to allow engine heat up, when specified temp reached it opens and let it flow and radiator tries to keep coolant cool.when it is broken it stucks or it acts slow or it wont acts at all. in your situation it is stuck open half way. it allows enough water to be heated but flow is limited to heat cabin heater.

2-if there are cabin heater selenoid/selenoids for two different temperature for cabin left and right, on some instance those selenoid valves to adjust cabin heater stuck open or closed like thermostate acts on first case. so heat is not enough to heat up cabin heater.

Hi,

The overheating and lack of cabin heat both point to a failed engine thermostat which would be stuck closed. At the warm up stage, the coolant stays in the engine block to bring the engine to efficient operating temperature, then it opens and circulates the coolant through the radiator and heat core. If the thermostat is stuck closed, the engine will overheat, and coolant will never reach the heater core, and you will not get cabin heat.

Blinking oil light at idle which goes away during driving could be a low oil level, but may also be a drop in oil pressue. You could have a clogged oil fliter (at best) pickup tube, or a failing oil pump.

check if your thermostate is working... is it having troubles getting to operating tempurature?
check your heater lines that run to the heater core and see if there is heat getting to and from the heater core if the thermostat is running properly...
if you have heat running to and from the heater core then check and make sure your heater controls in the van are switching between defrost and heat and floor properly
could be a heater box problem ....
when i had the same problem with my venture it turned out to be a plugged heater core and i replaced it

possiblt thermostat, how bad was the cooling system before it was serviced, recmd replace thermostate first, if you still have problem, reverse flush heater core to remove settlement from heater core

There are thermostates the will stick in the open postion1 this will cause you not to get heat if that is the issue. Air in the cooling system will cause this too. Or low coolant check your coolant level!

One or more of:

1. Your coolant is low
2. Your thermostat doesn't close and needs to be replaced
3. The valve from the cooling system to the heater core is stuck
4. Your heater core is clogged

it is either low on coolant or the thermostat is sticking

I had problems with a similar truck,a 1998 GMC diesel after checking to make sure the control cables were operating the blend door and blowing the mess of the heater core,I replace the thermostats.Still no heat turns out there was a small amount of debris collecting in the fitting for the inlet hose at the thermostat housing after removing it and blowing out the lines the heat was fine.