No heat

Coolant is full. No coolant in oil. Will have to check the rest after work today. Although the shop I took it to told me the fans were working. But, this could be an intermittent problem.

However, on the way to work today (outside temp 41 deg F) everything seemed to work fine. Even the heater.

This is after this morning going and filling it up at a gas station and having some problems. See previous posting. I am not sure what the outside temp was this morning, but the temp is supposed to drop all day.

Van has worked well the last few times I drove it, until this morning. Just as I pulled into work (roughly a 12 to 15 minute drive) the temperature gauge started into the red zone. And I had no heat coming out of the vents. I parked the van and opened the hood, both fans were working. I grabbed the upper radiator hose and it was still cool. I squeezed it a few times then shut the hood in disgust. I went to turn the van off and now the temp gauge is reading normal. I opened the hood again and touched the upper hose and it was starting to get warm. The outside temp is 17 deg F.

What is going on with this thing? Can a thermostat work intermittently?

Here is what I have done and it seems to have worked:
I drained some of the fluid out of the radiator and added straight antifreeze. I then drove it to work and on the way to work it started to climb in temperature (but never overheated).

It reached about 3/4 of the way to overheating and then dropped back to normal operating zone. It has worked fine ever since.

I noticed it was overheating only on really cold days, so I figured the antifreeze to water ratio must be off.

If anything changes in the next few days, I will updated this thread.

The van has gone through many recent repairs to fix this problem along with other symptoms, in the following order : - Changed thermostat > tuned vehincle > Changed water pump > changed thermostat > flushed radiator > flushed heater core > changed head gasket > replaced overflow hoses > performed coolant flush & replacement.

Still, the following symptoms exist :
- Temperature guage shows cold (1/3mark) on higher RPMs, and is in middle when idling
- engine & vehicle vibrate quite a bit on idle
- normal heat from heater when on idle but drops to luke warm at higher speeds/rpms.
- fuel efficiency has reduced from 20+ mpg to 17-18 mpg.
- no other warning lights/messages visible

During cold days my feet almost got a frostbite. Please advise. Thank you!

Are you suggesting a engine compression or cooling system compression test? I had the latter done with no issues. Engine runs powerful and with no misfires (if it were not firing all cylinders I would get a check engine light but I don't see any such lights). It only vibrates when on idle. Anything else to consider before going ahead with the engine compression test and other repairs?

Try changing your cabin filters. I had the same issue, and I found out about these cabin filters, and so I changed them and what a difference

I am really hoping you can help me figure out what is going on in my engine. Ok here is the story. We bought this van used with 152000 miles on it. Around 151000 miles on it we replaced the intake gaskets because they went bad. At 152000 even the head gaskets blew and it was cheaper to put an used engine in it instead of the repair. We purchased a used engine with 87000 miles on it. We have since put 5000 miles on it. Well while driving home today (on the freeway) the temp. Gauge shot up to the red and I had not heat. I limped it home. While driving the temp went down to a 1/4 on the gauge. Still no heat. The coolant is backed up in the resevoir. I am able to drive it for about 1.5 to 2 miles before it gets hot and then it goes down to 1/2 and then back up. Still no heat. PLEASE HELP!

There's a TON of people that have this exact same problem with Chevy Ventures. I was one of them... It is a MAJOR PAIN IN THE REAR to get the air out of the coolant system! Sounds like the problem.. also, b careful cuz ive been told that due to the aluminum heads, they are very prone to blown head gaskets, warping etc. after even only one overheat...
There is (actually two) bleeder screws on the coolant system. I use the one on the passenger side of the vehicle because its higher and better to let out extra air... Its located about ten inches to the left of the oil fill cap. It has a hex head (cant remember the size) and its very simple to bleed the air out by unscrewing it a few turns and bleed until coolant streams out. This process took me like two days of repeating until finally my temp gauge and everything is back to normal...

The answer I got from Niz76 was awesome to stop my overheating of my engine and get my heater to blow hot air in my 1997 Chevy venture. It took me 20 minutes to pop the rad cap, release the bleeder nut on the left hand side and start the van and squeeze the hoses on both sides while the van was running. As soon as the antifreeze started running out of the bleeder nut hole, I tightened the bleeder nut and put the rad cap back on tight and took the van for a boot around the block a few times. Problem fixed, no overheating, and awesome hot heat. THANKYOU

No heat, temp guage spikes and falls, replaced thermostat, burped the system(@ a garage)
checked all relays and fuses

TWO WORDS.

HEAD. GASKET TONS of articles on this and it's UNFORTUNATELY a COMMON PROBLEM. Its what happens when you take an aluminum head and place a rubber gasket between it and a cast iron block.

Before I got the answer from this site, my 1997 Chevy Venture heat gauge also would spike to red line hot and then drop down to cold and then back up to super hot and the heater was blowing cold air and I couldn't figure it out, what was causing the problem. I finally found that the small spout just under the rad cap that connects the overflow hose to the plastic overflow tank, was cracked on the bottom side and was spitting antifreeze onto the ground. As the engine would heat up and des pence my antifreeze out this crack it created air blockage in the whole line. I had to replace the rad as JB weld wasn't able to repair the crack. Once I got everything all back together, I still ran into the problem of engine overheating and no hot air coming from my heater because of the air getting into my system until I bled the line with rad cap off also and removing the bleeder bolt until antifreeze flowed out of hole and then I put the cap back on and the bleeder nut back on and tightened down and all was great

Has a new thermostat. No external coolant leaks. Could it be a blown head gasket?