air in cooling system?

[zchrisz]

hey guys i have this issue with my truck a 90 k1500 5.7 tbi, i replaced the water pump, and i noticed when starting in the morning to go to work, the temp gauge goes way high and then drops down, after this initial thermostat open it's fine the rest of the time i'm driving until it cools down again.

i've run the engine with the radiator cap off and have filled it up, it seems like there is air in there, yesterday on the way home from work i got stuck and the t-stat was not opening or blocked, the upper radiator hose felt like it had a lot of pressure and was cold, i pulled the cap off the radiator and all the coolant came out and the upper radiator hose got hot, i filled it up with water and it was fine after that....

the radiator, water pump, and thermostat is new.

i've used the block checker with the fluid, and there was no sign of combustion gasses in the radiator.

is it hard to bleed the air? i noticed the fluid goes up and down in the radiator and pours out every so often after the t-stat is opened.

 

[BOTTLEDZ28]

I use the following to bleed air from the cooling systems on my vehicles and have had great results. I park the truck on a slight hill with the front end facing uphill to help the air get out and just fill the funnel. I would try the hill method with a cap off and the heat on high and see what happens.

http://www.summitracing.com/parts/lil-24680?seid=srese1&gclid=CL78p9Tn3b4CFaQF7AodnQQApA

 

[96Z71ECSB]

Good advice from BOTTLEDZ28.
It does sound like there is still air in the system.
As suggested, turn the heat on high/full heat/on vent, leave the cap off the radiator, and let it idle until the thermostat opens.
Let the thermostat cycle several times and add coolant as the radiator level goes down.
One thing that helps speed up the process is to wedge something in the throttle linkage so it idles around 2000rpm.
Feel the air coming out the vents to make sure the air is hot after several cycles of the thermostat.
If the air is hot, drop the engine back to idle, and feel the air again. It should get slightly cooler but not cold.

If you get cold air out of the vents at idle, add coolant, and continue to bleed the system until the air is hot at idle.

Be aware that the "up hill method" works on some vehicles and not on others.
If the system won't bleed doing the "up hill method", then try bleeding the system on level ground.

Good luck!

 

[someotherguy]

Just FYI in these trucks, turning on the heat won't help anything, as there's no control valve to the heater core coolant flow; it circulates full time regardless of setting. (I think in some of the Vortec-era or maybe just on ones with rear heat, there's a vacuum-operated valve, though.) *Just re-read and saw the comments about feeling the air out of the vents, I guess that's useful but IMO not really a necessary step. Easy enough to watch what's going on at the radiator neck and add coolant as needed.

The "hill" trick is a good one and can also be replicated with jack stands or ramps if you don't have any hills or steep driveways nearby.

I like to drill a couple small holes in the flat area of the thermostat when I install a new one. Doesn't make enough difference to affect how it works, but allows air to slowly bleed through and work its way out of the system.

Richard

 

[98_k1500]

+1 on the drilling a hole in the thermostat. Keep your overflow tank full and it should bleed itself right out with a few cycles of coming up to temp and cooling back off.

 

[zchrisz]

thanks for the advice, i'll try bleeding it again, over flow is at correct level. i was thinking about the drill a couple holes trick in the thermostat, i've never experienced an issue like this on other sbc, although, it looks as if the upper radiator hose is higher than the radiator, this could be a possibility why it's sensitive to air

 

[Horns]

Take the T-Stat out, have one man on the throttle and one man with the hose spraying water into the radiator. Once it stops sucking the water down, it's got most of the air out.

Next time you flush the system, pull the CTS before you start dumping coolant in.