De-aeration of coolant

jp928

jp928

Well-Known Member
Just read some stuff on this, and cant find a mention here of 'aeration'. Has anybody tried it? Results? Basically I think it means using a separate header tank (higher than rad) and piping hoses from top of rad and top of engine to it so that air can escape there, and allow the radiator itself to be topped right off with zero air gap. This could be done on the V8 by running the top of inlet manifold hose to the header tank (T piece?).
Anybody think this will change anything on our cars? Is the plastic header tank on ours up to taking a pressure cap at the common 1 Bar/15psi?
thanks
john
 
Hi John,

I have not heard of this before, but to be honest, it is not difficult to expel air for the cooling system following a radiator removal or whatever.
1) With the engine idling, fill radiator to base of filler neck. Do not bring the engine up to temperature, there is no need for that. Put the cap on and go for a drive, 10 or 15 mins will be fine. Come home, turn the engine off and leave until the next morning.
2) Remove cap, start engine, the coolant level will have dropped as the air that was in the system now occupies that space. Fill to the base of the filler neck and put the cap on. The job is now done. If you were to look at it again the next day, assuming no leaks, with the engine cold the level will be just under the filler neck, just as it should be.

Ron.
 
Thanks Ron. Car I am looking at has a whitish plastic header tank connected to rad. It currently has a 'dead' cap - ie not a pressure cap, I assume that cap is on the rad. Are these header tanks able to hold pressure if fitted with a pressure cap, so they can act as a real header tank?
 
Yes a plastic expansion tank with a neck fitting for a pressure cap will hold pressure. I tried this out with a plain cap on the rad and a pressure cap on the expansion tank and it would have worked well if I had been using a water / glycol mix. However I am using Evans waterless coolant and with the expansion tank half full there was not enough room left for the expanding coolant, as Evans expands a lot.

I now have a 5 psi double seal cap and a recovery bottle. The rad is brimmed full at 3000 rpm, the cap fitted, a small amount of coolant in the recovery bottle with the rad overflow pipe going to the bottom, the coolant expands into the bottle and then gets sucked back into the rad on cooling down.
 
Sparky is fitted with a plastic header tank and is pressurised with the rest of the system, i.e. 15lb cap on the bottle, flat cap on the rad, with the hose fitted to the original overflow on the rad.

IMG_3830[1].JPG

I did get stuck in traffic on a really hot day and it did suffer rather badly. The engine temp went to 127°C and the bottle expanded with the heat and pressure, but it didn't let go. I did have to replace it though. It has gone down a bit in this pic, but did look like a balloon, and is covered in cracks.

IMG_3828.JPG
IMG_3780.JPG

I do think it would have been worse without the bottle, although he would have probably just chucked all of the water out and left me stranded.

Richard
 
I wonder if your rad cap was compatible with that tank ? There are different depths of cap and I suppose it is possible if a long cap was fitted to a shallow neck then it could over pressure ? Just surmising. Perhaps the tank was just old.
 
Richard,
I saw your post about the cracked header tank, but didnt recall it when I posted this query. Will watch out for getting the correct cap fitted. As an aside Porsche fitted a plastic header tank in the 928, the size of a small pumpkin, which tend to split where the two halves are joined at the mid point when they get old - which they all are now. To add insult to injury the RHD version is now ~ 3 times the price of the LHD unit - much lower volumes. When mine started to look dodgy I replaced it with a locally made alloy unit at a fraction of the price.
thanks
 
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