Vacuum bleeding cooling system?

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Has anyone heard of vacuum bleeding the cooling system to get rid of the trapped air, and does it work? I used a hand vacuum pump on my cooling system to remove any trapped air in the system. I got it up to 12 inches of vacuum before the main hoses collapsed, and ran the engine for a few minutes. I didn't see any air bubble from the inlet hose. The engine was not up to operating temps; it was around 160. It's a 2001 GM 5.3 V-8 engine
 
Doesn't work. Just fill the thing full of coolant and let it run @ 2000rpm untill the stat opens or it starts to show it's getting hotter than normal and shut it down, let it cool, refill and repeat.
 
Google "Airlift II". As long as your filling the cooling system, this will leave almost zero air in there if you do it properly. Have fun.
 
Hi,
Loobed - Many engine families require vacumm bleeding. Porsche for instance uses this system

Many cooling system problems such as cavitation and localised "hot spots" can occur through improper filling
 
The reverse flow GM systems can be very difficult to refill.

You may want to familiarize yourself with the factory recommended procedure. It solves a lot of problems for the do-it-yourselfer.

Running an improperly filled engine at 2000 rpm until it shows hot on the temp gauge is BEGGING for a problem!
 
The LSX, hence the 5.3 is not reversed cooled so nothing to worry about there. The LT1 was though. Should be as simple as flushing out my Trans Am. I flushed i,t drained it, filled it, ran it around the block, topped it off. Went to work checked it when I got home topped it off. That was 32,000 miles and 150 1/4 mile passes later with N20 and a nice size cam. Your 5.3 is identical architecture to my LS1/5.7.
Nothing special about it, you are not going to hurt it.

Just some info for you:

Remember 1992, when Chevy raved about the Gen II’s reverse-flow cooling? Well, reverse is, apparently, out. The new engine uses conventional pushrod V8 cooling. Coolant is pumped into the block, around the cylinders, up into the heads, then out to the radiator. The reason Gen II went reverse was that, to make the power Corvette Development wanted; it had to have a higher compression ratio (LT1, 10.2:1; LT4, 10.8:1). Higher compression made for detonation. The cooling system was revised to run the cylinder heads cooler as an antidetonant strategy, and to run the cylinder bores hotter for higher oil temperature and less friction. Clearly, reverse-flow cooling, the publicity darling of the Gen II engine, was really nothing more than a fix that allowed the limited cooling of the old Small-Block head to work with the higher compression necessary to reach the 300 horsepower level.

Air in the cooling system becomes problematic if it gets into the water passages surrounding the combustion chambers. This often causes localized boiling and that, in turn, allows hot spots to develop on chamber walls and they cause detonation. The problem with reverse flow is that with coolant flowing downward and air bubbles flowing upward; keeping air out of the Gen II cooling system was difficult.

Though the LS1 has a lower static compression ratio; its cylinder heads have improved combustion chamber design and intake ports that breathe better. Those features allow them to make more power. The clean-sheet-of-paper approach also allowed design of the cooling passages around the chambers to be more efficient such that the engine can put out more power than the Gen II but yet have coolant flow in the conventional direction to eliminate problems with aeration. With a better combustion chamber and water jacket design and improved antifriction technology in the block, pistons and rings; it made sense to go back to the normal-flow cooling system.

Like most engines of the last 20 years or so, the LS1 uses a 195 degree thermostat. Nominal coolant temperatures are similar to what we see in LT1/4 engines
 
Originally Posted By: SteveSRT8
The reverse flow GM systems can be very difficult to refill.

You may want to familiarize yourself with the factory recommended procedure. It solves a lot of problems for the do-it-yourselfer.

Running an improperly filled engine at 2000 rpm until it shows hot on the temp gauge is BEGGING for a problem!
True but this particular truck has a regular cooling system and theres no tricks to filling it other than what I described.

I remember those stupid VW vans that were a real pain to fill and a vacuum bleeder might help with those.

Even with the vacuum thing you still have to run the thing untill it warms up then top it off after it cools.
 
I don't know if I have reverse flow, but the thermostat is on the bottom hose and the water comes in the top hose. I think this is dumb because if the water is low because of a leak, there will be no flow of coolant into the engine. On the old style, top down, if the radiator was half full it could still cool the engine because the water was sucked from the bottom.
 
Originally Posted By: Loobed


I don't know if I have reverse flow, but the thermostat is on the bottom hose and the water comes in the top hose. I think this is dumb because if the water is low because of a leak, there will be no flow of coolant into the engine. On the old style, top down, if the radiator was half full it could still cool the engine because the water was sucked from the bottom.


I think there is a such thing as reverse thermostat. The water still flows the same way and not reverse cooled just that the flow through the radiator is regulated into the engine instead of out. I think GM did this on some designs too. Edit: Sorry, i just saw your engine is a late-Model LS. Anyway this isn't anything new GM has done the reverse thermostat before. I think it should actually be easier to get the air out if anything if you run it till T-stat opens.
 
Last edited:
Originally Posted By: ls1mike
The LSX, hence the 5.3 is not reversed cooled so nothing to worry about there. The LT1 was though. Should be as simple as flushing out my Trans Am. I flushed i,t drained it, filled it, ran it around the block, topped it off. Went to work checked it when I got home topped it off. That was 32,000 miles and 150 1/4 mile passes later with N20 and a nice size cam. Your 5.3 is identical architecture to my LS1/5.7.
Nothing special about it, you are not going to hurt it.

Just some info for you:

Remember 1992, when Chevy raved about the Gen II’s reverse-flow cooling? Well, reverse is, apparently, out. The new engine uses conventional pushrod V8 cooling. Coolant is pumped into the block, around the cylinders, up into the heads, then out to the radiator. The reason Gen II went reverse was that, to make the power Corvette Development wanted; it had to have a higher compression ratio (LT1, 10.2:1; LT4, 10.8:1). Higher compression made for detonation. The cooling system was revised to run the cylinder heads cooler as an antidetonant strategy, and to run the cylinder bores hotter for higher oil temperature and less friction. Clearly, reverse-flow cooling, the publicity darling of the Gen II engine, was really nothing more than a fix that allowed the limited cooling of the old Small-Block head to work with the higher compression necessary to reach the 300 horsepower level.

Air in the cooling system becomes problematic if it gets into the water passages surrounding the combustion chambers. This often causes localized boiling and that, in turn, allows hot spots to develop on chamber walls and they cause detonation. The problem with reverse flow is that with coolant flowing downward and air bubbles flowing upward; keeping air out of the Gen II cooling system was difficult.

Though the LS1 has a lower static compression ratio; its cylinder heads have improved combustion chamber design and intake ports that breathe better. Those features allow them to make more power. The clean-sheet-of-paper approach also allowed design of the cooling passages around the chambers to be more efficient such that the engine can put out more power than the Gen II but yet have coolant flow in the conventional direction to eliminate problems with aeration. With a better combustion chamber and water jacket design and improved antifriction technology in the block, pistons and rings; it made sense to go back to the normal-flow cooling system.

Like most engines of the last 20 years or so, the LS1 uses a 195 degree thermostat. Nominal coolant temperatures are similar to what we see in LT1/4 engines


One interesting story is GM had problems getting their reverse cooling system to work. An inventor had a working example he designed. Something about the air bleed hole had to be a certain smaller size. GM tricked the inventor and kept the his car overnight, but really reversed engineered his design. GM told him no thanks, then later released his design into production without paying royalties. There was a lawsuit and that was the allegations. I don't know if all that had any bearing on GM not using reverse-cooling after that or not.
 
back 10 years ago or so , when the airlift vac bleeders came out
they work good. But i noticed i would have a rad leak in some of
the customer cars after work I did.
the vacuum will pull the rubber seal of the rad end tank in on higher km cars.
so I stopped using it.
This is my experience, I thought to share .
this is with the aluminum rad with plastic end tanks using
rubber seals between.
 
Thanks that is a good tid bit. I assume the airlift doesn't pressure feed. I think it's best to pressure feed the coolant when vaccuuming. Did you just stop using coolant exchangers all together after that experience?
 
yes, I stopped using them. Customers were unhappy after I did , say a leaking headgasket, or timing cover. then after finishing and using the airlift bleeder I had to quote a radiator. I knew was dry before any repairs.
The one I used and still have, hooks up to the rad or bottle were the cap would go. then using shop air it pulls a vacuum in the entire cooling system. you can see the hoses pull in flat and the guage goes near 30" vacuum. Then another hose is full of coolant attached to a container is opened which filles the system leaving absolutly no air. It is a great idea, expecially for the hard to bleed systems because there is no bleeding after because there is no air.
But I must stand behind my work, so I take the extra time and
bleed the cooling system the conventional way.
 
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