hey guys i just replaced my t-stat. and i was just wondering how do i bleed the air out of my cooling system because my temps are all over the place. also, sometimes theres alot of pressure when i take my radiator cap off, is that normal? thanks in advance

 

When I change t-stats, I always drill a single 1/8" hole in the housing. I then line up this hole with the front of the engine and then add the gasket and rest of the assembly. The if you jack up the front end has high as you can get it the air can excape through this hole even if the t-stat has not opened yet.

Jack up the front of the car as high as you can get (be sure to block the rear wheels). Take off the raditor cap and start the car and run it until it gets to operating temp. Keep adding water to top it off.

 

ok thanks alot, really appreciate it!

 

I would propose an alternate approach.

I would suggest that most problems occuring after a coolant system service is because the system is initially overfilled AND the radiator cap is left off too long, preventing the normal pressure build-up.

The pressure build-up is important to prevent spot-boiling, expansion of existing air bubbles into flow-blocking air-pockets, and the normal movement of air so it can be scavenged into the designed location (e.g. pressure tanks or radiator).

Suggest the following procedure:

1. when car is cool, and not running, bring the coolant level to a maximum of 2 inches below the fill neck (applies to either radiator or pressure tank).
2. Add coolant to the overflow tank (non-pressured tank) to the full hot level.
2. put the pressure cap on (aka radiator cap).
3. start the engine and after 1/2 minute hold the RPM's at 2,000 for 3-5 minutes.

IF the temps seem normal, take the car for short drive around town, and if temps stay ok, your done. Over the next couple of days, the system will top itself off by drawing in coolant from the overflow bottle. All you need to do is to check it daily and assure the overflow bottle level stays between hot and cold levels.

Remember do not push the engine until at least 3 full heat-up/cool down cycles (to assure the anti-freeze and and water have completely mixed).

If by chance the temps do not seem normal after the 3-5 minutes at 2k RPM's, then turn off the engine, allow it to fully cool. Likely after it has cooled and you then open the pressure cap, the fluid may be very low. Therefore, start the procedure again, as likely there was a large air bubble inside the block which should now have moved around to the designed location.

Obvious other things to keep in mind.

The pressure cap must be in good condition and both be able to hold back the designed pressure as well as allow coolant to be sucked back in when the cooling down creates a vacume.

Any coolant leaks may prevent the normal build-up of pressure and the build-up of vacume. Be sure to try and have these fixed.

 

ok, i did the first approach and everything seemed normal after a short drive. but ill keep an eye on it over the next couple of days. thanks for your input as well

 

JTOOMBS,

your welcome.

BTW, just noticed I did not answer your other question ("also, sometimes theres alot of pressure when i take my radiator cap off, is that normal?").

Yes, pressure is normal. Once the engine has warmed-up, the pressure should be at/near the pressure of the pressure (radiator) cap. This pressure is important as it keeps the coolant in a liquid state, instead of it boiling, which can create flow-blocking air pockets.

Remember the reason to NOT open the pressure (radiator) cap when the engine is hot, is as much to prevent getting burned as to not inhibit the normal cool-down and resultant vacume which draws back in the typically small amount of coolant which was pushed into the overflow bottle and will be drawn back into the system as it cools.