No cooling system pressure

[stilly]

Hi all,
Last year I replaced my head gaskets and everything seems to be running o.k. Since that time, I've never had pressure in my cooling system. The water pump is still pumping, and the engine is relatively steady at 200 degrees..., most of the time. I had the system pressure checked a while ago (prior to head replacement). They said that my frost plugs had rusted somewhat and had small leaks. Two questions: 1) Has anyone tackled those frost plugs and how difficult is it? 2)What are consequences of running my 6.2 without pressure in my cooling system? Thanks.

[TimK]

A pressurised cooling system provides two advantages. A higher pressure raises the boiling point of the cooling system. Where water typically boils at 212 degrees F at sea level, it will boil at 225 degrees F at a higher pressure. (I don't remember what that value would be.) A system that starts to boil will contain a lot of gas (water vapor)bubbles and the water will not circulate properly. If you lose circulation you also loose cooling. Keep in mind, that although your temp guage says 200 degrees F, that there are locations in the water jacket that may be cooler and warmer then this.

The other advantage of a pressurised cooling system is that it minimizes cavitation in the water pump. At the RPM the 6.2L turns I really do not know if cavitiation is ever an issue.

The first place I would check, if your not maintaining pressure is the radiator cap. Your freeze plugs are located below the water line of the cooling system. If they are leaking a little then you should seem some corrosion and green fluid around the plugs. I have looked at my freeze plugs and I would probably wait until I remove the engine to work on those.

TimK

[ 10-31-2003, 08:37 PM: Message edited by: TimK ]

[catmandoo]

stilly you didn't say what you have 2wd 4x4? some softplugs can be a bear to get at anyway if it was leaking that bad you would see anti-freeze on the driveway. and if i remember right (and feel free to correct me) the pressure raises boiling point at a rate of like 3 degrees per lb so 15 lbs would give you 257 degrees. think i'd try a new rad cap.

[stilly]

Thanks all. It's a 4/4 2/3 ton Suburban. I've done the radiator cap exchange twice, so unless I'm extremely unlucky with a bad cap, my only idea are those darn freeze plugs. Can't I just JB weld those suckers?

[catmandoo]

get a pressure pump that fits on the rad and pump it up to 15 lbs .it will either hold or slowly go down and if so you should be able to see or here it leaking.check hose clamps upper rad hose at the rad is good for this.

[stilly]

It looks to be the freeze plugs. One on the driver's side is leaking and another on the passenger side behind a motor mount! Are there six freeze plugs??? I suppose there's no fixin' that without pulling the engine huh?

On another point..., I did do the pressure test and it was holding pressure, albiet very slowing lossing it. The thing I don't get is when I run the truck to 200 degrees, turn it off and open the radiator, there's no pressure. Any ideas?

[catmandoo]

they can be replaced in the vehicle but they can be a pain to get to (like behind the motor mount)i used to change them all the time in my shop you probably are better off pulling motor as the steel motormount bracket is hell to get off in the truck,if it was any of the other ones i would replace them in the truck.