baxsom

what is causing this, i put in a new thermostat after flushing my cooling system. i tested the tstat in boiling water and a candy thermometer and it opend up just at the temp it is supposed to.
i get finished with the flush and install the thermostat.

after 10 mins the car is overheating. the upper radiator hose is rock hard.

i let it cool down and unbolt the tstat housing and put it all back together without the thermostat this time and the coolant temp barely got over 210.

i retested the thermostat in boiling water and it opened up again.

strange. i am going to replace it with one of those fail safe models i guess but id like to know what might have been causing it not to open when installed.

BigBlockTank

Was it installed upside down?

Peterbuilt

Did you put it in upside down? PG.

Reggie Dunlop

If the t-stat was installed correctly (the point will "point" towards the radiator and the spring will point down) the only other problem you could have caused is an air bubble or air lock, which is rare with a vette because the top of the radiator sits below the t-stat. A sure fire way to prevent the air lock is to drill a small hole (1/8" or so ) in the flange of the t-stat. If you are adversed to drilling the bleed hole, install the t-stat, fill the radiator to 4" below the top, start and run the engine at 1,000 rpm. Now look in the radiator with a flashlight, as the temp rises to the t-stat opening temp you should start to see coolant flow from the upper tubes in the radiator. Also, most t-stats won't start to open until they are at or past the rated temp, and they won't be fully open until 10 or 15 degrees beyond the rated temp - you probably noticed this when you tested it with the candy thermometer.

baxsom

this t stat already had a bleed hole in it,
it was installed with the spring going down into the intake. the tip section is up.
i dont see how i can fill the radiator to be able to see the water line, the fill cap is on the expansion tank by the right fender. no fill hole in the radiator.
tstat was rated at 195 the gauge pegged the needle. even if it didnt fully open until 10 or so past it shouldnt peg the needle at idle in 10 minutes with the factory rated tstat.

...Roger...

Try filling the cooling system through the thermostat opening and then install the therm and housing then the radiator.That usually does it.

'75

Did you indicate it got to 210 deg idling with out the thermostat? If so, you have other problems.

baxsom

it has always idled at 210 with the needle straight up on the gauge. thats only 15 degrees over the thermostat rating. well out of the red zone.

when its over 100 outside it idles in traffic around 225 but goes back to 210 when moving.

baxsom

that is how i filled it in the first place.

larrywalk

Sounds like it is time to replace your temp sensor - at idle, your coolant temp should be quite close to the thermostat value.

As far as the upper hose becoming hard, this is normal as the water pressure increases as the coolant warms up. The upper pressure is limited by the radiator cap which opens to let the expanding coolant into the coolant recovery tank.

...Roger...

Hmmm Well that should insure the water pump is full but I actually start my fill through the plug in the top of the pump (because I'm a bit ****).With the hole in the thermostat you should have flow.Not saying 210 is great but not knowing what your outside temp is and how accurate your gauge is 210 minus the therm. doesnt bring up "huge" red flags. After running minus the thermostat did you redrain the system to reinstall the thermostat or just remove the housing and reinstall ?

Mike Ward

Arn't you the guy on the other website that just backflushed his engine?

You've probably clogged the radiator with engine gunk.

baxsom

i thought that could have been it but temp is fine without thermostat and water runs through the radiator easily

Rockn-Roll

If your temperature gauge is reading right then you are experiencing the effect of reduced coolant flow on a system that is just barely adequate. The thermostat is most likely opening, but the thermostat is restricting flow just enough to slow the rate of heat extraction to the point where it isn't doing a good enough job and the temperature of the coolant is rising to compensate...heat flow will increase with temperature difference.

Also, as pointed out...the temperature gauge should be reading about 160º at idle without a thermostat if the coolant system was doing it's job. So, it sounds like either your temperature gauge and/or sensor are not compatible or are malfunctioning, and/or something else in the system is not doing it's job such as water pump may not be spinning fast enough i.e. someone put in a larger pump pulley, plugged lines in the radiator core, or perhaps the problem is insufficient air flow through the radiator i.e. fan not turning fast enough, fan too small, missing shroud, etc.

But, if the problem is air flow then the temp should drop while driving above 40mph...as long as you still have the air dam. If this is not the case, then the most probable reason is plugged lines in the radiator core which requires removing the radiator and giving it a nice hot acid bath.

sweethence

just out of curiosity, does the lower hose have the spring in it?

Reggie Dunlop

Here's the thing - IF the t-stat was the ONLY thing changed, then that is the problem. And if the temp gauge reading was fine before, that just confirms it. Put the old stat back in and check it. I can tell you I have experienced similar things with the Mr. Gasket high flow stat (the goofy looking one with the long spring on it). Switching back to the original functioning part will solve your puzzle.