Classic 3.5 v8 edelbrock carb1984

Hi Guys i have a strange overheating problem from startup
Start the car when cold and the temp slowly rises on the gauge until it gets into the red then the thermostat opens and it goes to normal and stays there never moves,
when it gets to the red if i get out and take the cap of the reservoir it makes a hiss and the temp gauge goes to normal, Now this has only started since i changed the timing cover because i found a crack in it, it has never done it before i changed the cover, originally i thought it was the thermostat but ive changed it and its still doing it, the old one tested ok
any ideas guys, all help would be appreciated
Im wondering if a blocked bypass hose from the thermostat housing to the water pump might be the cause, what you all think ?
as I say as soon as the stat opens everything is fine
thanks all

Cristoforo said:

Hi Guys i have a strange overheating problem from startup
Start the car when cold and the temp slowly rises on the gauge until it gets into the red then the thermostat opens and it goes to normal and stays there never moves,
when it gets to the red if i get out and take the cap of the reservoir it makes a hiss and the temp gauge goes to normal, Now this has only started since i changed the timing cover because i found a crack in it, it has never done it before i changed the cover, originally i thought it was the thermostat but ive changed it and its still doing it, the old one tested ok
any ideas guys, all help would be appreciated
Im wondering if a blocked bypass hose from the thermostat housing to the water pump might be the cause, what you all think ?
as I say as soon as the stat opens everything is fine
thanks all

Click to expand...

Air in the system perhaps? It should make a hiss when the coolant is hot and you undo the cap, the systems is supposed to be pressurised.

Cristoforo said:

Hi Guys i have a strange overheating problem from startup
Start the car when cold and the temp slowly rises on the gauge until it gets into the red then the thermostat opens and it goes to normal and stays there never moves,
when it gets to the red if i get out and take the cap of the reservoir it makes a hiss and the temp gauge goes to normal, Now this has only started since i changed the timing cover because i found a crack in it, it has never done it before i changed the cover, originally i thought it was the thermostat but ive changed it and its still doing it, the old one tested ok
any ideas guys, all help would be appreciated
Im wondering if a blocked bypass hose from the thermostat housing to the water pump might be the cause, what you all think ?
as I say as soon as the stat opens everything is fine
thanks all

Click to expand...

Does it hiss if you leave it overnight to cool down?

Grrrrrr said:

Does it hiss if you leave it overnight to cool down?

Click to expand...

Hi No no hiss when it's cooled down it's like the water pump is putting pressure into the system, as if the pump is pushing to a stop end, I'm going to take the bypass hose of and look inside for a blockage or delamination

Heat water and there will always be pressure as it expands with heat. The pressure cap is probably set to around 14psi.

If i did not create pressure in the system as it got hot it would boil , as the pressure increases the boiling point.

Pressure from the wife increases my boiling point

Update the bypass hose had started to delaminate and collapse internally causing a blockage, new one ordered see how we go
Thanks everyone for your input