I am making this suggestion one more time as in my previous post #54 since it didn't get any traction there.

I suggested there might have been a hose put back in the wrong place. I don’t know if this is physically possible however my thinking was that somehow the thermostat was being bypassed and not able to do its job.

Looks like Freeze has replaced the stat 3 times already so I think we can get away from the stat as being a problem. Even if it went in backwards it would be overheating. I don’t know how many hoses were removed during the original repair.

If you want to run a test, we know the temperature is good at idle. Start the electric fans manually and see if the temperature drops. This would simulate driving to some degree. It should definitely not fall near the 100* mark.

It is also apparent this problem did not exist until the heater core repair was done or Freeze would have indicated this problem was there prior.

Although I have no real proof, it just does not seem that air would cause this problem. It seems like with the inferred readings the engine and hoses are cooling down equally in all areas together (no hot or cold spots).

 

The way to be sure you have no air in your cooling system is to LOOK into the filler with the thermostat open, engine above idle.
I don't think air in your system is going to cause the symptoms you experience, the only thing that makes sense is that your thermostat is being bypassed, is or is forced open when you are on the road.

 

ok

Here's the deal. I replaced the thermostat minutes ago with an OEM part from the Chevy dealer,and refilled the coolant levels. The temps at idle seem to be fine and I drove it around town at 35-40 mph and the temp does still fall back to about 160 degrees on the gauge but never went lower than that. However, i still haven't been on the Interstate yet so tomorrow on the way to work will tell me if it is still going to go to 100 degrees on the gauge or not. The other question I have is the coolant level in the reservoir. When I opened it up to check yesterday it was just below the level where you could see the fluid flowing into the reservoir so I called the Shop where I had the system flushed and they said that That is where it is suppose to be. Does that sound right to anybody. It seems that it should be topped off right to the top of the reservoir not halfway down into the reservoir. I have only refilled it to that same level at this time.

Thanks for the inputs.

FREEZE

 

I'll check the book tonight. I think it should be full, what is the overflow tank level at? The system should fill the overflow tank as the coolant heats up during normal operation. When you shut off the engine and the coolant cools the resulting decrease in mass should draw the fluid back into the system. Your reservoir should be full at all times. Sounds like we are making progress, I think the OEM thermostat is set at 160 degrees.

 

If yours is like mine it should be full. They are probably thinking you are looking at your overflow.

 

Just a suggestion/thought here... considering the heater core started this problem, why don't you unhook the core lines from under the hood and hook them together... now obviously you won't have heat, but test and see if your engine temperatures come up. Also another thought... If something were to be causing high water pressure at >2000RPMs, is it possible it could literally be blowing the themostat open? Just a thought.

Also, reservoir should only be about half full because when the fluid heats up it creates pressure and expands into the reservoir, so if it were full it would overflow. As the fluid cools, or leaks out if you have a leak, the radiator sucks fluid back out of the reservoir like a Venturi vacuum.

AFAIK, your reservoir IS your overflow. that's the way it was on every car i've ever seen. All operating coolant is stored within the radiator, correct me if I'm wrong though.

 

I checked the maintenance manual. It says: The high fill reservoir provides a coolant fill point and a central cooling system air bleed location. The cooling fluid level in the high fill reservoir should be maintained to the top of the filler neck. A sensor in the high fill reservoir is used to determine coolant level. When the amount of coolant falls below the recommended level, a warning lamp in the instrument panel will illuminate. I always add coolant to the recovery reservoir when the engine is cold. Fill to the fluid level cold position on the dip stick. The system will then service it self (numerous fluid additions may be necessary). It will be interesting to see what your coolant temperature is when the engine is working at freeway speeds.

 

Just wondering, what temperature stat did you buy?

The reservoir surge tank should always be full, that’s how these systems work. Regardless, if it was filled not completely, when the engine cools down from hot, it will draw coolant from the overflow tank provided you have coolant in the overflow tank.

After a few cooling and heating cycles the surge tank should be full, and the overflow tank should stabilize (provided you did not let it run dry when there was a demand for coolant from the tank).

 

Well I put the 4th thermostat in the vehicle last night. It was an OEM stat from the Chevrolet Dealership and The temps are back to normal range. I finally had heat for the first time in a month today. Now that it is working, a little background for everyone. I had bought a fail safe thermostat for 19.99 at the local Auto Zone, It was the most expensive so I figure it must be the best. HAHA. When the temps wouldn't come up on the vehicle, I immediately thought something I had done was wrong. I have worked on cars since I was about 10 and with 37 years of wrench turning I felt that I knew enough to do this simple job. I got a lot of great ideas from people on here and I tried all of them. I was told that it was the thermostat and so I took the advice and went down and bought a new thermostat, another 19.99 thinking there is no way that I could get 2 that were bad from the same store. When I pulled the new old one out and put the 2nd new one in , it looked good, was not open and I then wished that it would have been in the fail safe mode which it was not. I put the second thermostat in which ended in the same results. I then took the vehicle to a Local Corvette specialty shop and had them flush and burp the system since that idea had been floated here too. Started vehicle up and still had the same results.
So far changed the heater core-- a very difficult and tedious job 59 bucks and 2 days of work
Changed the original thermostat that appeared to be working

Replaced with new fail safe 19.99 thermostat --Auto Zone

Buy $69 Laser Temp sensor to check heat flow around hoses and heater core --Northern Tools

Changed 2nd Thermostat with another 19.99 thermostat -- Auto Zone

Took vehicle to Corvette Shop and had system flushed and coolant changed $129.00

Finally order original thermostat from Chevy dealer $13.99 install and Waala-- Temps are all fine with heat in car on way to work and home today.

So tonight i take all three other thermostats and put them in pan of water and start to heat them up on the stove.
Original thermostat opens first at about 120 degrees-- that's a problem. But it is 21 years old.
2nd new thermostat opens immediately after at 130 degrees-- this is a 195 degree thermostat
3rd thermostat opens within 5 seconds at 135 degrees which is the same thermostat as the 2nd.

I then go to garbage can and pull out the box and finally realize what is going wrong throughout this entire process.

MADE IN CHINA AHHHHHHHHHHHHHHH CRAP!!!!!!!!

Buyer beware when you buy new parts for your AMERICAN MADE BEAUTY!

I will never let this happen again.

Thanks to all of you for all your help and suggestions. I almost lost my mind and was close to trading her in on a new Camaro on Wednesday night.

Hey Honey look

I just saved us $ 30,000.00 dollars

 

and again.

 

I just want to thank Humfreeze for the write up on all the technical items right up to the point of completion. To many people get some info and go off into the night never to be seen again and the Forum members who gave their best opinions never knew what the outcome was.

This is how it should be, my Thanks...

 

Thank you for teling the "End of the Story" so we al know what happened.
As for A-Zone, The only thing I'll use from that store comes in a can or bottle!

 

Good reading material. I always learn something on this forum.
Glad your car is fixed.

 

Wait Humfreeze, youre not done. Get those garbage thermostats back to autozone and get your money back!
BTW, what brand were the failsafe thermostats?

 

Very informative. I had never even heard of a failsafe thermostat until this thread. TKS

 

That was the best read all year! Glad it worked out for ya....oh and forget the camaro-get a challenger...........

 

 

Hot Rod Roy was the first to tell you to put the thermostat in a pan of water and heat the water.
I'm with jon0108, take those defective thermostats back to autozone and get your money back!

 

Thanks Hum For all the info. Ive been following this from the start and talked this over with my son (he's pretty good with a wrench) to see what his take was on this. Can't remember ever seeing a situation just like this so this was interesting reading and a eye opener. JUST GLAD YOU GOT IT FIXED AND HAVE HEAT AGAIN.

 

Update I took the thermostats back to Auto Zone and even though they are warranted, the Manager has refused to refund my money due to the fact that he does not believe that 2 thermostats can be bad. I am currently writing a letter to Corporate headquarters to try and resolve this issue. I have dealt with this particular AutoZone for years to the point that they even know my name when I walk through the door and since they have recently had a Management change, things have turned for the worse at this particular store.