How do you bleed the coolant system properly?
- Thread starter toy264
- Start date
John,
For initial fill I would raise the front wheels of the car approx 6" off the ground, remove both caps and the temp gauge sender unit from the intake manifold if fitted ( This will allow the engine block etc to purge any air if the thermostat is fitted). Now start to fill the system at the radiator header tank until the coolant level reach's the cap level at the radiator( you may have to wait for a couple of minutes for the level to stabilize as the block will also be partially filled by this time), replace that cap and continue to fill at the engine bay header tank until coolant reach's the sender unit fitting, now replace the temp gauge sender unit and top off the header tank with coolant. Dont rush it and the coolant will self purge any small air locks in the tubes etc. Start & Run the motor at a fast idle (2500rpm) until you feel some heat going forward in the 'top' tube, then shut it down and allow to cool. Recheck coolant level, it should not require much more to top it off. If it does repeat the warm-up process again.
Jac Mac
For initial fill I would raise the front wheels of the car approx 6" off the ground, remove both caps and the temp gauge sender unit from the intake manifold if fitted ( This will allow the engine block etc to purge any air if the thermostat is fitted). Now start to fill the system at the radiator header tank until the coolant level reach's the cap level at the radiator( you may have to wait for a couple of minutes for the level to stabilize as the block will also be partially filled by this time), replace that cap and continue to fill at the engine bay header tank until coolant reach's the sender unit fitting, now replace the temp gauge sender unit and top off the header tank with coolant. Dont rush it and the coolant will self purge any small air locks in the tubes etc. Start & Run the motor at a fast idle (2500rpm) until you feel some heat going forward in the 'top' tube, then shut it down and allow to cool. Recheck coolant level, it should not require much more to top it off. If it does repeat the warm-up process again.
Jac Mac
Peter Delaney
GT40s Supporter
John, I had huge problems getting all the air out initially, but finally settled on a really simple setup using small brass quarter-turn stop-cocks at the 2 highest points in the coolant system :
- I got a small spigot brazed into the top of the rad & fitted one tap there. Plastic hose from the tap to a temporary catch tank on the ground.
- The 2nd little tap is installed into the side of the brass housing that takes the temp sender for the water temp gauge - front-right at the top of the DC&O inlet manifold. The one has a permanent plastic hose snaking down to just below the chassis - water falls onto the ground.
To bleed the system, I just open the taps one at a time & keep topping up the main header tube. Once all the air seems to have gone, I then warm the engine up to about 40degC, then open the little taps again & watch for the air bubbles to stop running out (easy to see with the plastic tubes).
Opening the taps relieves the pressure in the system, so you can then take the pressure cap off the header tube to top things up without getting into trouble.
When you bleed off, you will need to keep an eye on the water level in the header tube - if it goes below the level of the outlet tube to the thermostat, you will get more air in & have to start again ! So, only bleed off about 20-30mls at a time before checking & topping up.
Make sure that you have the heater core valve open during this whole exercise, and that you give the engine a bit of a rev between bleeds - this seems to expel any air in the heater core quite well.
Once you have done the initial static bleed, you should only have to do the warm-up bleed 2 or 3 times before you have no bubbles in the plastic bleed tubes - then you are all done.
Hope this helps a bit.
Kind Regards,
Peter D.
- I got a small spigot brazed into the top of the rad & fitted one tap there. Plastic hose from the tap to a temporary catch tank on the ground.
- The 2nd little tap is installed into the side of the brass housing that takes the temp sender for the water temp gauge - front-right at the top of the DC&O inlet manifold. The one has a permanent plastic hose snaking down to just below the chassis - water falls onto the ground.
To bleed the system, I just open the taps one at a time & keep topping up the main header tube. Once all the air seems to have gone, I then warm the engine up to about 40degC, then open the little taps again & watch for the air bubbles to stop running out (easy to see with the plastic tubes).
Opening the taps relieves the pressure in the system, so you can then take the pressure cap off the header tube to top things up without getting into trouble.
When you bleed off, you will need to keep an eye on the water level in the header tube - if it goes below the level of the outlet tube to the thermostat, you will get more air in & have to start again ! So, only bleed off about 20-30mls at a time before checking & topping up.
Make sure that you have the heater core valve open during this whole exercise, and that you give the engine a bit of a rev between bleeds - this seems to expel any air in the heater core quite well.
Once you have done the initial static bleed, you should only have to do the warm-up bleed 2 or 3 times before you have no bubbles in the plastic bleed tubes - then you are all done.
Hope this helps a bit.
Kind Regards,
Peter D.
John,
May I suggest that you fabricate and plumb a bleed line from the pump "discharge", usually a nipple for 5/8" hose on the pump itself, for supply to the heater core, to the header tank inlet. Ideally you would reduce this down to a #4 AN (1/4"). This will continually bleed the entire system system once the thermostat opens. Drilling #40 hole in the thermostat will also purge gasses while it is closed
Regards,
Scott
May I suggest that you fabricate and plumb a bleed line from the pump "discharge", usually a nipple for 5/8" hose on the pump itself, for supply to the heater core, to the header tank inlet. Ideally you would reduce this down to a #4 AN (1/4"). This will continually bleed the entire system system once the thermostat opens. Drilling #40 hole in the thermostat will also purge gasses while it is closed
Regards,
Scott
Pat Buckley
GT40s Supporter
Blue Point tools sells a tool/device that, using shop air, creates a vacuum in the cooling system which is then replaced with your coolant.
It is foolproof, works every time, and eliminates all the contortions that we have all been put through in tying to eliminate dreaded air pockets.
It is foolproof, works every time, and eliminates all the contortions that we have all been put through in tying to eliminate dreaded air pockets.
Pat is right - Vacuum filling does eliminate the vast majority of air in the system. You might get an odd burp here and there but that should not be a big enough bubble to cause any concern.
On sale for $10 US is this A/C Vacuum unit from those perveyors of (TIC) "High Quality" Asian components Harbor Fright : Harbor Freight Tools - Quality Tools at the Lowest Prices
I happen to have this unit and it can be adapted to connect to your coolant recovery line to draw the vacuum needed..
On sale for $10 US is this A/C Vacuum unit from those perveyors of (TIC) "High Quality" Asian components Harbor Fright : Harbor Freight Tools - Quality Tools at the Lowest Prices
I happen to have this unit and it can be adapted to connect to your coolant recovery line to draw the vacuum needed..
John, I have a 3/8" (small diameter) bleed line from the top of my radiator and a line coming out of the intake maniford. My engine tilts slightly upward at the front so the fitting is at the front end of the manifold. If your engine is tilted down at the front, run the bleed line from the back of the intake. These two lines are tee'ed together and run to a port on the header tank where the system is filled from, which I keep filled to the top. I also use an overflow tank that has a small amount of coolant in it all the time. The bleeding is constant. The last time I drained and refilled I just kept checking the header tank and filled it as necessary as well as keeping the small level of coolant in the overflow tank. The system bleeds itself and is full (does not need water) after a few cycles. I run a 5/8" line from the bottom of the header tank to one of the heater ports on the water pump (other port is capped) to fill the system.
Scott-
I don't have a thermostat fitting in the manifold (is a thermostat really a neccessary component here?), and the secondary 5/8" water pump discharge is plugged. I could just tap it for a 1/4" NPT X #4 AN fitting and run a line up to the Header tank. Would it be worthwhile to go ahead and add a port in the manifold through to the rear water outlets from the heads since all but the front two are blocked? (Why did Ford do that anyway?) As near as I can tell, the engine sits dead level. I know this was addressed in another thread dealing with steam pockets, but I'm more concerned with bleeding the system at this stage.
Thanks for your advice guys, I didn't how much I didn't know 'till I started reading the posts in this forum!
John,
If it were me I'd opt for some means of temp regulation. I believe a thermostat will promote faster warming of the eng / oil, reducing wear overall. If you have NO thermostat and your header tank is the highest point in the plumbing, you already have self bleeding cooling system. You are correct if you want to run the line from the water pump to the tank. But instead of drilling an existing fitting, buy an AN-to-pipe union of the appropriate size. The rear water ports if utilised will certainly promote more even temps across the engine block and heads, and maybe allowing additional ignition timing advance.
Hope it helps,
Scott
If it were me I'd opt for some means of temp regulation. I believe a thermostat will promote faster warming of the eng / oil, reducing wear overall. If you have NO thermostat and your header tank is the highest point in the plumbing, you already have self bleeding cooling system. You are correct if you want to run the line from the water pump to the tank. But instead of drilling an existing fitting, buy an AN-to-pipe union of the appropriate size. The rear water ports if utilised will certainly promote more even temps across the engine block and heads, and maybe allowing additional ignition timing advance.
Hope it helps,
Scott
You are going to want a thermostat or at least a restrictor plate for coolant return. It is actually possible for the water to move too quickly through the system and hurt cooling efficiency. The fast moving coolant does not have time to soak up engine heat and then lose the heat in the radiator.
My .02
My .02
Dutton
Lifetime Supporter
John,
Andy's right - you definitely want to slow down the water flow enough to suck a bit of heat out of the cylinders. If your water is moving too fast, the cooling system is just a little too fragile at a minimum, more likely it won't work as you hoped it would.
When racing years ago, an easy to cure to a sticking thermostat was to remove its guts leaving, for all intents and purposes, a flow restrictor - which worked flawlessly.
Best,
T.
Andy's right - you definitely want to slow down the water flow enough to suck a bit of heat out of the cylinders. If your water is moving too fast, the cooling system is just a little too fragile at a minimum, more likely it won't work as you hoped it would.
When racing years ago, an easy to cure to a sticking thermostat was to remove its guts leaving, for all intents and purposes, a flow restrictor - which worked flawlessly.
Best,
T.
Andy-
Forgive me if I respectfully disagree with your proposal that slower flow will result in better heat transfer. I would never represent myself as either experienced or educated in the automotive field, but I do have some experience in air cooled heat exchangers in the natural gas industry. In that field you’ll typically see 20’ by 20’ fin and tube air cooled exchangers used to cool pipeline compressors driven by very large engines. In that particular application the goal is to have the highest coolant velocity consistent with laminar (straight-line) flow in the tubes, constrained of course by costs, available components, etc.).
The reason for this is that as the flow slows down, a unit volume of coolant first spends more time in the compressor and reaches a higher temperature, then more in the heat exchanger where it cools off more. The net heat transfer is the same, but the differential temperature between compressor and exchanger increases at reduced flows. At some point the compressor over-temps, goes off-line, and very bad things begin happening.
Increasing the rate of flow, up to a point, will bring the two temperatures closer together. A unit volume has less time to cool down in the exchanger, but spends less time heating up as well. What limits this is that at some point the liquid flow will become turbulent near the tube walls, and the rate of heat transfer abruptly falls off.
Now, whether any of this is applicable to us and our projects, I don’t know, and putting a restriction in the line, as you recommend, may very well be a good idea. I hope someone who’s tried it will chime in.
You're dead right there John. The faster coolant flow the better for heat transfer but it is my understanding that a restictor is required to maintain water pressure in the block so the water flow is maintained in tighter spots that would otherwise form steam pockets and it also delays pump cavitation. It's a pressure issue not a flow or heat transfer issue.
Here's what Davies Craig has to say about it :-
The 'pump too fast' notion is an old wive's tale. We have been doing R&D for many years on several test rigs and have never been able to pump faster and lose less heat. In all car engines, when the mechanical pump reaches cavitation speed, the flow rate drops resulting in a reduction of heat loss and the temperature goes up. It seems like the flow rate is too fast because it is assumed that the pump is not cavitating. Another popular notion for mechanical and/or electric water pumps is that as flow rate increases and the coolant spends less time in the radiator, it is not sufficiently cooled. It should be remembered however, that as the flow rate increases, the heat transfer from the engine is also reduced and there is less heat in the coolant to be lost in the radiator - it all balances out!
Cheers,
Here's what Davies Craig has to say about it :-
The 'pump too fast' notion is an old wive's tale. We have been doing R&D for many years on several test rigs and have never been able to pump faster and lose less heat. In all car engines, when the mechanical pump reaches cavitation speed, the flow rate drops resulting in a reduction of heat loss and the temperature goes up. It seems like the flow rate is too fast because it is assumed that the pump is not cavitating. Another popular notion for mechanical and/or electric water pumps is that as flow rate increases and the coolant spends less time in the radiator, it is not sufficiently cooled. It should be remembered however, that as the flow rate increases, the heat transfer from the engine is also reduced and there is less heat in the coolant to be lost in the radiator - it all balances out!
Cheers,
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