Ok im really succombing tothe terrors of catastrophic water loss...and have looked (for the nth time) at the faq suggstions and a few things bother me..

1. I have a 940 but my expansion tank isnt as described
2. I HATE the idea of drilling holes in (no doubt) expensive peices of volvo kit
3. I hate mechanical switches
4. I cant easily source a float switch rated above 100 degrees c..

so i was playing with a few ideas and came up with a nice idea..question is does it work (can it be made to work....)

if you removed the rubber hose from the bottom of the expansion tank and inserted a small length of said hose, them a piece of metal pipe (copper, ally whatever) and connected the hose to this and clipped everything tight and refilled you would then have a metal contact electrically isolated from the car by rubber except for the fluid in it connecting it to the block...i.e. it would be earther to the block by the fluid. If you lost fluid therefore you would loose the earth (or loose a substantial amount of earthing).

now the question is (need to gt busy with a meter etc...and this has just occured to me) do you have ENOUGH earth there to hold a small relay open give n12 volts applied to the other side of it....?

if the answer is yes...then you can wire the relay to fire a buzzer light whatever and this set up has several advantages:-

1. no hole in tank, no rubber washer to age etc.
2. its fail safe..i.e if it fails the light comes on
3. it may well be possible to make it solid state..i.e. no moving parts!
4. it shouldnt be effected by cornering/cold coolent levels etc..
5. it should be cheap.


anyone got any thoughts or no the resistance qualities of water/coolant mixture (before i take up my multi meter and go check?)

I have installed four of these float swithches in our fleet of 700 series turbo cars, and I have not had one leak. I do use a cone shaped grinding wheel to make a bevel for the o-ring on the outside of the tank to fit in.

Both switches listed in the 700/900 FAQ are rated for 100º C.

Thanks John...in the FAQ it says switches rated for above 100 deg c...I can get 100 deg ones eaasy, much above that and it gets interesting...

im sure its an easy job...just me being tricky and looking for the improved mouse trap i guess...still like they say if the mopuse trap works....why fix it..

It would be ill advised to introduce an electrical charge into the cooling system, as corrosion could result. I've read quite a bit in the trade rags about keeping voltage out of the coolant to avoid corrosion and possible cooling system damage as a result. Voltage leaks in the wrong places could theoretically cause pitting and chalking of the surfaces, and perhaps ultimately wear holes in places.

I'm just calling this from the top of my head. I don't really have any specific examples of this, but I have read quite a bit about keeping voltage in the coolant BELOW a very minimal (VERY minimal) amount because of the potential damage.

For that reason, I would say that your idea is good with respect to no moving parts, but not very good for the cooling system.

Others may differ on this opinion.
--
1992 940 wagon, low miles
as well as others.

I'm positive you're right.

We need to use photons instead of electrons.

--
Don Foster (near Cape Cod, MA)

yeh i guess it would be like creating an etch tank when you think on...shesh...and the earlier 7 series had this feature as standard ...go figure....grrrr...

i just hate hate hate drilling tanks..its (a) putting a hole in something i dont want holes in (b) creating a stres point in a stressed structure and (c) a PITA to get the bits....

there must be a good solution here..its doing it non invasively thats the problem i guess...i was thinking about a presure switch at one point but thats not easy either...

maybee i will just go and take my car the local dealer nad ge a square tank retro-fitted with the float in it...problem is the car confuses them everytime they see it as volvo (typically) made something they didnt make....i.e. its a 940 that isnt really... perhaps...maybee... (eg 760 wiring loom...go figure)

If you depend on conductivity between a probe and ground via the coolant, keep in mind thatbecause of salts and ions (there's metal in that coolant), and high humidity, you'll have a substantial leakage path up the rubber insulator, down the plastic walls, to and through the coolant, and to the block.

I'd bet that the coolant won't carry the current you need for the relay coil, but you could amplify it using an FET (very high input impedance).

How about doing something with the cap? If you screw up, a new cap is cheaper than the expansion jug.

How about some type of optical sensor, much as the Delco (and other) batteries had the "magic eye?"

How about a float (inside the jug) with a magnet that activates a reed switch or hall sensor outside the tank? No holes......

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Don Foster (near Cape Cod, MA)

lol don i have already thought about most of the above...

yeh the fluid on the hose walls kinda is a worry.,..but i bet the resistance jumps big time....


the cap..been there..it has a presure release machanism in it...cant go drilling there...


optical...yeah now that has primise...except clear (or nearly clear liquid and opaque tank...did think about a laser to a photoresistor but i kinda doubt that the water would be enough to stop or obscure the beam...

cant go to the float idea (would love to) as i cant work out a way to accurately position it in the tank without drilling the dreded hole or glueing it(good luck on ploy prop). whatever i want NO chance of anything comming loose and making its way into the cooling galleries in th block...

thanks for the thoughts though...think i may have to just test bed it...

"...cant work out a way to accurately position it in the tank without drilling..."

What about an insert that fits into the filling hole and is secured, or clamped down, when you screw on the cap -- but that doesn't interfere with the cap's operation?

--
Don Foster (near Cape Cod, MA)

Will the square tank replace your current tank? When I did my rad replacement last year, an OEM square tank with float was only about $25 from an auto parts store in the Bronx ($35 from newandusedvolvoparts.com). Threw in the "level guard" sensor for $20 at Borton, and I was good to go. Just clips in. No drilling, no mess. The only question would be if the pressure requirements are the same between the round tank and the square one. Since my original was square, I wouldn't know. But that info is probably readily available.

sounds like a good thought...