Radiator Pressure

[hooD]

   What would cause the cooling system not to build pressure at the radiator cap?  The cap is good ( I have 3 caps that all do the same thing) but there is no pressure on the system.  I have no coolant leaks that I know of, and the antifreeze level is not going low.  I changed the heater hoses and did a coolant flush 2 weeks ago.  I am not over heating, the temp gauge is reading 190-195 while driving and around 210 if stuck in traffic.

The top radiator hose should be hard with pressure after driving and mine isn't.

[Chryco Psycho]

is the neck of the rad damaged so the cap cannot properly seal up

[hooD]

is the neck of the rad damaged so the cap cannot properly seal up

No, the neck is in great shape.  I checked the dip stick for any signs of coolant leakage mixed in the oil and saw none. 

[Changin Gears]

There are 2 commonly avaiable types of caps.  The difference is, in the center of the part that goes into the radiator, there is a metal disc.  If the disc flops around, it is for a car with the coolant recovery tank.  If you don't have the tank you need the other type (should be tight against the rubber seal.

[solarguy]

My upper rad hose doesn't stay hard the whole time car is running  either.  I thought it was normal.  My coolant level is about 1 1/2 inches below top of filler, which gives plenty of room for expansion.  Under normal crusing around in the heat in S Florida, runs normal range on temp guage , no pinging.  If I beat on the car in the heat of the day, I can make temp guage rise and then rad hose if firm.  My thermostat is new and tested good before install.  With the cap off and engine running, I see slight movement of coolant but not a huge "current",  again which I think is normal.  Are you showing any signs of overheating?  Engine ping under load?  I'd like to hear the consensus on this. 

[Changin Gears]

My upper hose (all my cars, new and old) gets tight with just a few minutes of driving, never even come close to overheating.

[mrob]

I think Changin Gears is right. Take a look at the pic in the link. Disregard the fact that the pic shows a billet radiator cap. See the metal disc in the center of the rubber seal?(that seats against the radiator cap neck) If that metal disc is loose (moves around freely), there's no way that pressure will build up in the cooling system. The pressure just bleeds off through the overflow hose. Here's the link:

http://cgi.ebay.com/ebaymotors/BILLET-CHROME-RADIATOR-CAP-CHEVY-GM-FORD-MOPAR-DODGE-_W0QQcmdZViewItemQQhashZitem518f72d2fcQQitemZ350299017980QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

On an open cooling system, that disc must seat against the rubber seal below it with some spring pressure.

[hooD]

There are 2 commonly avaiable types of caps.  The difference is, in the center of the part that goes into the radiator, there is a metal disc.  If the disc flops around, it is for a car with the coolant recovery tank.  If you don't have the tank you need the other type (should be tight against the rubber seal.

   My cap has the floppy center disk, so I guess it's wrong for my cooling system.  I do not have a coolant recovery tank.  Thanks! 
              Will the temperature read any lower once I get the correct cap and the system becomes pressurized?

[MEK-Dangerfield]

              Will the temperature read any lower once I get the correct cap and the system becomes pressurized?

Yes.

[Changin Gears]

This is the kind of fix I like, $5 at Walmart, not having to pulling the heads.

I wouldn't worry about 210 stuck in summer traffic.

[miketyler]

its funny, mine never builds up pressure either. Gets hot pretty quick and has anew cap.

[mopar12372]

funny thing is this is a common problem --> people blame it on the thermostat being stuck open and replace it to find out the cap is leaking into the reservoir .
the cooling system cools under pressure to keep the engine from building steam . yes the engine should run cooler if other problems done exist.

[solarguy]

hooD,

Did the differnt style cap solve the problem?  If so, please post part number so I can see the differnce from mine.  Thanks

[hooD]

hooD,

Did the differnt style cap solve the problem?  If so, please post part number so I can see the differnce from mine.  Thanks

Hello Garrett,
I bought a $5 radiator cap from O'Reilly's and it worked.  I have pressure on the cooling system again.  And guess what... this cap is the same design as all the other caps.  It has the small metal button on the end.


Murray Caps & Stats - Standard Radiator Cap
Part Number: 7616

    * 16 Lbs.
    * UPC: 799304076162

[solarguy]

Thanks for the follow-up,    glad you got it fixed.       My cap must be tired too.  I'm just curious though, does that little disk on the bottom hang loose or is it tight, vented cap or non-vented.  Thanks again