Diagnosis confirmation

Just need an expert to confirm my diagnosis of a problem on my Chev Astro. My son comes home and says it's not blowing any heat. Blower is working , but just cold air. The temperature gauge was climbing as I let it idle in the driveway, but no heat. Isays I need a new thermostat, which I'm planning on changing in the morning. Am I right? Thanks

If there is coolant, and the water pump isn't borked, then the thermo-ma-stat is the most likely culprit.

If the thermo-ma-stat in question happens to be on a Chevy Astro I recommend replacement of the vehicle, preferably with something like a Olds Vista Cruiser if you actually need to carry much.

Actually, the darned thing has been a pretty good vehicle for the last 14 years and 250,000 miles. I can't complain. Thanks for the input.

If the engine temps are climbing normally, I doubt it is the thermostat. Low coolant levels will sometimes cause no heat. With the engine up to temp, check the heater hoses and see if they are hot. If they are, then the problem is probably in the heat/ac box or controls. The temp control door is probably stuck in ac mode. In older Chevys they were vacuum operated. I don't know about the newer ones.There is also a valve in most heater circuits than can get stuck in the closed position.

Good luck.

Low coolant or a failed waterpump are more likely imo.

I checked the coolant level first and it was fine. I didn't check the temp of the heater hoses. The temp gauge was reading well above the normal operating range.The motor was on the verge of overheating.The control system is vacuum operated, but I could hear something moving in the dash as I turned the temperature knob up and down. I'll check the hoses in the morning. Thanks Guys.

Your last post makes the thermostat the most likely culprit - and the easiest to fix. To check, just take it out and put it back together and see if it works. Don't run this way long -- bad for the engine since it will take a long time to heat up.

yes... thermostat or low coolant... if you are doing the stat.. might as well do the pump and hoses while you are there...

I have to do this outdoors, in Michigan. I think I'll just do the T-stat for now ! And, IIRC, there was a new water pump put on it 2 or 3 years ago. I'll look through the file to see if there's a receipt ,just to be sure.

I can't go along with the thermostat idea. All the thermostat does is block the coolants path to the radiator so it gets hot and stays at a predetermined temp by opening and closing. You say the temp is hot, therefore the the coolant passing through the heater core should be hot, as well. This would seem to rule out the thermostat. You said it had plenty of coolant when you checked. That would seem to rule out the low coolant theory. Since it sounds like the engine is getting TOO hot, yet the heater is not putting out hot air and the coolant level is normal, it leads me to believe you have a low flow condition that could very possibly be the water pump. Yeah, I'd be checking the temperature of hoses.

I had a brain fart - can't be the thermostat. Carzan has it right.

Another "me too" - if you get no heat and it looks like the van is almost overheating on the gauge, it can't be the thermostat. Pretty much all heater circuits are plumbed in on the block side of the thermostat so that the occupants get defrosted before any coolant circulates through the radiator.

Another vote for 'check the coolant hoses', plus I'd recheck the water pump because these symptoms can point to a broken wapu.

If he had done some work on the cooling system recently I would suggest a bubble of air around the pump, but since that doesn't sound like the case, the pump sound like a thing to check after coolant levels.

...also, make sure the coolant level you are checking is the actual system level, not just the overflow bottle level...

I went out and checked it first thing this morning when it was stone cold. The overflow bottle was empty, so I assumed it was sucked dry as the engine cooled. Filled it again and went for a short drive. It was blowing heat and the temperature gauge was sitting at it's normal reading of 70 degrees C. Came home and checked the overflow bottle and had to top it up to the "Full Hot" line. Between last night and this morning I put in close to a gallon of coolant, so maybe the system air-locked or the pump cavitated. Don't know where it's going ,but I'll keep a close eye on it for the next while.No wet floor on the passenger side under the heater, no white smoke out the tailpipe, no goofy looking oil, rad coolant looked good,too. I'll probably take it down to the local garage and have them pressure test the cooling system just to see if a leak shows. Thanks for the input everyone.

Smell the exhaust, if it smells sweet.......

I was going to suggest looking at the heat activation switches, if they're vacuum actuated it doesn't take much dry rot to make them stop working.

Definitely not a T-Stat.

Dan

I have automatic climate control in my Aurora, also had no heat. but my outside thermometer said it was 197 degrees out.

swapped the outside temp sensor and problem solved

I had a thermostat fail on my Astro. Symptoms were no heat and motor would not warm up at all. Even with the radiator completely blocked with cardboard, it would not get warm enough to provide any meaningful heat. I also had a different heater related failure a different winter. It was simply a broken vacuum line that fed the dampers that open and close the doors that direct air to the heater core.

Neither of these would cause the van to actually run hot. No heat and running hot usually means low coolant or low coolant flow. If there is a proper amount of coolant in the radiator, then the problem is the water pump. Things like head gaskets will cause overheating, but the interior heat ought to work great until it consumes the coolant.

Checking water pump operation is as simple as feeling the temperature of the hoses as the motor warms up, and looking in the filler hole on the radiator if it has one. Should be pretty easy to diagnose.

-Chris

It's been working normally for the last 24 hours and all I did was add coolant. I had to teach my son to read the gauges and know where the normal running is on each. We'll see if it's really fixed or not.

The low coolant was obviously the cause. 2nd problem is to find out why it was low. You already said you were going to do that.

Another thing you might consider. Seeing as how you are in Michigan, no heat, and over heating can also be caused by frozen coolant hoses. If your mix of antifreeze/water mix is weak the hoses will freeze before the block and you will get no coolant flow to anything. If you added strait glycol, you probably solved that problem. Keep us posted.

Pause... The heater core on a 4.3 gets flow regardless of the thermostat. The heater core is a bypass of the stat, so it gets flow regardless or stat position.

I'd be more concerned about the water pump, or a blockage somewhere. That is what I would eliminate first.