presure

hi my 70 small block vet heats up and there is no pressure in the rad or hoses is this good or bad thanks  

this could be bad...

does the system hold water?????

you might want to first change the radiator cap..   they have been known to NOT hold pressure as some of them have the small disc in the center of the rubber seal that is NOT spring loaded in the upwards position.. it just dangles waiting for coolant to push it closed.. a great idea.. except.. it does not always work..

do you have a radiator pressure tester???     some parts stores have these in the Loan a tools section behind the parts counter.. where you pay for the loaner tool.. and can return it for a refund within 2 weeks or so..




this is where to start at..    the pressure tester allows you to pressurize the system to 13 pounds pressure and let it sit to see if there are any leaks...  

With the cap off, does the water in the radiator get hot?  Do you have an analog gauge to read the water temp?  If so, see if the temp goes down a bit at the rated thermostat setting.  Your stat may be sticking.  

If I put a new thermostat in, I always drill a couple of 3/16 inch holes in the perimeter of the stat.  This serves as an internal bypass to help bleed air from the system and prevent hot spots.  Not directly related to your problem, but thought I would mention this.  

One other thing.  Don't put the thermostat in upside down   It will open eventually, but waaaay too late.  

THANKS GUYS I HAVE A LAZER GUAGE AND READS 210 THE SAME AS THE GUAGE IN THE CAR.I RENTED A PREASER TESTER AND A NEW CAP AND SAW THE FLUID WAS DOWN A LITTLE. I WILL TEST OUT THE PREASER TESTER AND GET BACK TO YOU GUYS THANKS FOR YOUR HELP  

I guess the big question is, "where are you taking the reading with the laser?".  Try taking it at the base of the thermostat housing, the upper radiator hose and the top of the radiator and compare it with your car's reading.  

i bet he is going to find just a funky cap that would not hold pressure..

i sure hope that the cap has failed recently.. as if the system has NOT been pressurized for a while.. the thermal cycling will have an odd effect on the hoses.. when heated and cooled over a longer time without the pressure in the system.. they tend to NOT like to last when pressure is restored..  

Interesting thought, do they make a cap that reads PSI?  That would be cool (figuratively speaking).  

i have not seen one..  but thats interesting.. really old cars as i recall had thermometers..

i saw a water pump test mule one time... it had pressure and temp gauges screwed into almost every possible place..  seems there is a LOT of pressure built up behind the thermostat.. this increases the boiling point of the coolant in the block...  i was not allowed to see the mule in operation.. i was let in that the inblock and head pressure was quite high at moderate Rpms to keep the hot spots near the exhaust ports and valve seats from boiling the coolant  creating hot spots... causing a runaway engine overheating  as the steam fills the top of the engine and prevents heat from the coolant from touching the thermostat bulb ..  

Usually when a radiator goes bad it blow the coolant out the over flow. Not because it overheated, because the cap won't hold pressure and then when your collant is low thats when it over heats and the damage can start.

I would fill the cooling system cold. So you don't have pressure drops because of temperature changes. Then with a coolant pressure tester put 16 psi on the system. The pressure shouldn't drop maybe 2 psi it at all.