Coolant pressure sensor

[The Great Pretender]

it now runs 2 psi higher coolant pressure. .
but this may be a good thing as it may raise the boiling point of the coolant.

Or reach cap pressure sooner.

[Northern Bongolow]

maybe, thats what the was for. time will tell.
the weird thing is though, all 3 of my temp gauges read the same as before the change. i would like to think its more efficient, by pushing more coolant around, the pressure gauge is monitoring down stream from the water pump so it kinda makes sense to me.
but then again

[The Great Pretender]

Where down stream?

[Driver+Passengers]

An extra half to 3/4 inch of coolant would give you +2psi.

[The Great Pretender]

An extra half to 3/4 inch of coolant would give you +2psi.

I have noticed that. As the tank is trying to do two jobs it has to compromise.
Its main purpose is degassing with a small area for expansion.

Feeding the overflow pipe into a further bottle or tank that was open to atmosphere with the pipe covered with coolant would be better than the standard system.

[Driver+Passengers]

Feeding the overflow pipe into a further bottle or tank that was open to atmosphere with the pipe covered with coolant would be better than the standard system.

Can you explain why? I can't see it yet...

[teenmal]

Feeding the overflow pipe into a further bottle or tank that was open to atmosphere with the pipe covered with coolant would be better than the standard system.

Can you explain why? I can't see it yet...

I cannot see what the benefits would be.

[Northern Bongolow]

Where down stream?

the pressure sensor is mounted in the pipe that goes from rad top to the expansion tank, the main circuit when the stat is closed and the heater circuit loop, as i see it this is the controlling circuit.

[Northern Bongolow]

An extra half to 3/4 inch of coolant would give you +2psi.

thanks matt, you have stated this previously, but as usual i didnt listen . the coolant level is about 15mm higher than the top full mark when cold, so will amend and see what happens .

as stated above this is near where the pressure is monitored.

[Driver+Passengers]

A different type/concentration of antifreeze filled to the same level may also result in a change in running pressure, due to a change in the average volumetric thermal expansion coefficient of the mix, but only very marginally. Level is far more likely to affect it.

Actually, just ran some calculations - a drop from 50% to 40% antifreeze may result in a 0.5psi drop in running pressure due to the higher TEC of the antifreeze.

[Northern Bongolow]

right----------- . been out and adjusted level to the correct cold level mark, then out for a test flight, still got 2psi up with new pump .
but as you point out above the pressure may vary with the mix of coolant / water, and i did put the same coolant back in with a litre or 2 of water to help during the bleed process, so maybe thats it. i will investigate later.

all temps are normal, and the fans still kick in at 13 psi as they did before. when the fans kick in on first stage it reduces the pressure from 13 psi down to 10 psi, where before it reduced it to 8 psi. .

[The Great Pretender]

Feeding the overflow pipe into a further bottle or tank that was open to atmosphere with the pipe covered with coolant would be better than the standard system.

Can you explain why? I can't see it yet...

Justs gives more room for expansion.
With the system in good health it is belts n braces, but if there is a problem instead of dumping the coolant onto the floor it draws it back in when the system cools.

[The Great Pretender]

I have spoken to Matt about my previous alteration of the thermostat position to the outlet of the head.
I have since reverted back to the original stat position and made a restrictor with pressure sensor take off points each side of the restrictor and temperature take off point.



I have observed that there is minimal difference in pressure either side of the restrictor at any revs and the pressure is only controlled by coolant temperature until the stat opens, and then, well you probably wouldn’t believe me………….



http://s72.beta.photobucket.com/user/up ... 9.mp4.html

I have at last got around to moving the pressure take off 15mm to the other side of the restrictor.



The differential in pressure fluctuation from pre to post restrictor surprised me as the reading is taken just 5mm past the restrictor.

http://s72.beta.photobucket.com/user/up ... 2.mp4.html

[Driver+Passengers]

...

Can you help me get my head around this by summarising your thoughts and observations for the pressure readings pre- and post-restriction, perhaps for each of stat closed, open and fully-open (ie bypass closed)? Presumably difficult to reliably test the latter without disconnecting the rad fans...?

[The Great Pretender]

Interesting isn’t it Matt, it is doing what it was expected to do, but………………. I am surprised that the restrictor completely negates the pumps rise and fall in pressure.
The bypass needs to be closed to allow the pressure to rise with revs to 25 psi, until closed the pump only increases pressure by 1 or 2 psi while revving.

This helps the engine when working hard.
Consider a fully loaded Bongo or towing a heavy load in a hilly or mountain area, the engine will be at high revs producing lots of power and heat, the standard Bongo relies on heat alone to raise the pressure until it reaches cap pressure.
Coolant will boil in the head under these conditions producing gas pockets around the exhaust valve area, raising the pressure raises the boiling point allowing more heat to be removed from the head. Will this stop localised boiling? Probably not, but it will reduce it to the minimum the system is capable of.

I could increase the pressure to around 30 psi by simply fitting a smaller restrictor, giving the Bongo around 1Bar of extra protection over standard.