over heating

[pjbizjak]

OK guys any help would be appreciated, my 68 z/28 is over heating just idling in the driveway. It has a 180 degree thermostat, clutch fan, 3 row radiator, basic z/28 trim. Radiator was cleaned checked and flushed out, 15# radiator cap, thermostat changed out.motor is basically stock but bored 40 over and new J&E domed pistons. water pump new and water circulates when thermostat opens up but still overheats and blows hoses off.

[Tinkerr]

Does the engine produce any white smoke/steam out of the exhaust? Any water in the oil?It will look the coffee with a lot of cream.

[william]

Ensure that you don't have a reverse-rotation water pump.

[bertfam]

When you say overheating, what temperature are you talking about and have you verified it with a laser thermometer?

Ed

[169INDY]

"Calling" the link to the John Z Cooling system article

Someone post a clickable link?

Jim

[bertfam]

"Calling" the link to the John Z Cooling system article

Someone post a clickable link?

You mean THIS ONE?

Ed

[WorkinProgress]

Are you using the original fan blade, and do you have a fan shroud in place?

                                                      - Warren

[Charley]

If you start it up with the cap off do you ever see the water flowing after it starts warming up ?

[uscrichter]

Is this a fresh rebuild? may have an air pocket in cooling jacket.

[pjbizjak]

Original 5 blade fan with shroud,can feel good air flow thru radiator, no white smoke, no water in oil, can see water circulating with cap off, but still gets hot and blows out of the radiator cap hole, fresh rebuild (air pocket?). factory heat gauge only goes up to 1/4 mark on gauge temp degree unkown.

[Mike S]

You can use a low cost infrared thermometer sold at Harbor Freight. They work great at measuring temps across a motor as well as exhaust manifolds. Or, a meat type thermometer will work good too. Something like a turkey thermometer you can buy at a dollar store.

Mike

[bertfam]

Blowing hoses off isn't a sign of over heating, but a sign of over pressure. Especially since your temperature gauge is only reading a quarter of the way. Pressure is dictated by the radiator cap, so pull that and see what happens. You may have a defective cap and it's not venting at the correct pressure (15 pounds). Water coming out of the radiator at the cap when the cap is off is normal due to expansion. It "should" stop when the car reaches operating temperature.

However, like I said before, see what temperatures you're getting with the laser thermometer.

Ed

[uscrichter]

A lot of times when a freshly rebuilt engine is fired up it may have air pockets in the high point of the water ports and need purging, and they create steam within the motor which could cause that exact problem, the solution is to make sure the engine is level and may require jacking the rear of the car and with the thermostat removed from the water neck ad water slowly while the water circulates through the motor, I have done this successfully on several occasions, seems to happen more frequently with big blocks.

[Mike S]

  I had a reproduction radiator cap I bought from LI Corvettes that kept seeping when my 396 heated up. An infrared thermometer showed the radiator around 180F-190F. I bought another reproduction cap that was advertised to maintain the correct 15PSI and it's been fine since I installed it last year.

Mike

[TODD]

"fresh rebuild" Did you rebuild the heads? tell us a little more about this rebuild. My guess:
Only a bad head gasket or worse a cracked head will pressurize coolant system and not all coolant leaks let water by into oil/exhaust. Need a more information about rebuild?