Colin Mill

OK, here are the results of my initial round of tests. First of all, I looked at what resistance in place of the sensor was needed to get the gauge to read various temperatures. As mentioned the gauge is somewhat sticky so some tapping was needed to get it to settle (amazingly, engine vibration alone wasn't enough 😬) Gauge reading.......Effective sensor resistance 40C...................600 ohms 60C..................440 ohms 80C..................200 ohms 100C.................130 ohms 120C...................75 ohms As for the sensor I used a contact thermometer on the club foot close to the gauge sensor and when the contact thermometer was registering 80C the gauge sensor was at 230 ohms suggesting that the gauge slightly under-reads at 80C. Since my engine does not naturally get above 80C I will need to get the sensor out and do my further testing in a water bath. Interestingly, I tried using an IR thermometer on the club foot and, presumably because of convection from the exhaust the surface temperature seen by the IR thermometer was well above the contact thermometer readings. I have tried to fit the gauge requirements to a standard NTC thermistor and the best fit at the important top end of the gauge is obtained by a thermistor with a B value of 3800k but this is not too good at the bottom of the gauge. I'll be better able to sort this out once I have some better reading of the sensor itself.

This is not so much about how to make your car run on pure water as a way of running a business on pure bull-s**t - a far more common and, unfortunately, successful endevour.

Hi Jon Just spent a few fun hours looking at this both from the gauge point of view and the sensor. I'll try to tidy up the results and post them in a bit. However, the first thing I noticed is that the gauge is quite sticky so one really needs a tame woodpecker to get the needle settled otherwise the readings can be all over the place. Anyway, I have a preliminary conclusion - the temperature gauge on a Caterham can be relied on to tell you that a Caterham is fitted with a temperature gauge 😬

Water injection, as others have mentioned, has been around for a very long time both in piston engines and gas turbines. What you have to ask yourself is why, given the simplicity of the technique, has it not been widely adopted by the main-stream car manufacturers. Edited by - Colin Mill on 2 Jun 2008 09:05:59

No need for a separate kit for this on a K series Caterham. The K series engine has a built-in water induction system - on every intake stroke water is admitted to the cylinder via an annular gap between the top of the liner and the cylinder head. Unfortunately the performance advantages when this system is fully functional (it can take several 1000 miles before it runs in) are modest and short lived. 😬

Hi Jon It's OK I realise now that all I need to do is work backwards from the gauge and find out what resistance in place of the sensor gives what readings. With luck I'll get time to do this some time this week.

Hi Johnty Do you have the resistance vs temperature curve for the sensor or just even a couple of spot values? From two points it would be possible to work out the R0 and K values and find a good quality thermistor to use instead of these sensors that seem to fail so often.

Hi Roger I would be interested in this as I might well decide to make my own tank for experimentation. BTW does anyone know the diameter of the water pump impeller and some idea what the ratio of engine revs to pump revs is? I ask because I would like to do the sums to calculate the possible pressure differential at various revs. I have been surprised at how high the pressure is coming out of small centrifugal pumps (like some screen wash pumps) so perhaps this could be a factor in Peter's measurements. I'm starting to think that the idea of removing the water stat and using an automatic radiator blind might not be such a silly idea after all. Edited to say that from pictures etc I reckon the pump is about a 60mm diameter rotor turning at engine rpm. So at 4000 rpm this would have a stall pressure of about 0.7 bar. Edited by - Colin Mill on 31 May 2008 14:19:41

I'm going to see what Evalution want to make up a special - since the stock ones are about 65 quid I guess it will be serious 😬 I'm not jumping just yet however as I want to have a play with the idea of using a small pump (a screen washer pump may well be enough) in conjunction with a pressure transducer and the inevitable microcontroller to pre-pressurise the system. I know its overkill but it could be a very light solution.

Are you looking for an aluminium one?

In going for an uprated pressure cap I guess there are two considerations. Firstly, what increase in boiling point will the higher pressure give.? Looking at the tables I have for water the 1bar pressure raises the boiling point from 100C to 120C (antifreeze/water mix boils at a above 100C but the lift in boiling point will still be about 20C). Going from 1 bar to 1.7 bar (about 25psi) only lifts the boiling point another 10C. So I guess the question is will that 10C be significant The next thing is will the system stand the extra pressure. My guess is that the big diameter hoses are the things that are the limiting factor. It's easy to work out the stresses involved - the largest stress is the one trying to split the pipe down its length (the stress trying to rip it along a circumference is only half as big). Anyway, a 1.25 inch diameter pipe at 20psi has a force of 25 lbs trying to pull apart the two halves of the pipe for every inch of length. So as a crude test you could simply try pulling a 1 inch off-cut of pipe apart with 25 lbs (plus safety factor) between two rods slid into the tube. My guess is that any half decent rad hose will cope with 20psi quite easily.

I'm thinking that there may be another solution to this problem but to see if its a goer I wondered what people thought was the perfect way for the pressure to behave. Would it be ideal if the pressure rose quickly almost as soon as the engine was started to, say, 13psi and maintain this value until some time after the engine was stopped - say 5 minutes? Or should it only be pressurised after some temperature is reached? Any thoughts gratefully received.

I must confess I like nice simple cooling systems of the old-fashioned kind as they never give any trouble. My 1963 Massey Ferguson goes from one year to the next without a problem - look in the rad to see that the level is right (it's never wrong!) and go. Flush it out every few years and re-fill. It has a 13psi cap and an open vent pipe (like everything else from the 1960s)

Hi Bri Yes, that is why I'm keen to get rid of the Rover 'pressure' cap and have a Stant cap. From the earlier comments about pressures of about 1 Bar I guess the Rover cap is supposed to vent at about 15psi but who knows?? With a Stant cap on an 'airless' system the Stant cap lifts to release water as soon as the water pressure gets to 13psi (or whatever the rating of the cap) which, as you say, with the incompressibility of water happens as the water starts to heat up. Just to do the sums, the cubic expansivity of water is 210E-6 per deg C and the cubic expansivity of aluminium ( 3 times the linear expansivity) is 70E-6 per deg C. So the effective expansivity of water in ali is = (210 - 70) E-6 = 140 E-6. Taking the system capacity as about 5 litres and the temperature rise as typically 80 degrees gives us 5000 x 80 x 140E-6 = 56cc of water expelled via the cap. The expansivity of ethylene glycol is 570E-6 per Deg C so with pure antifreeze you would expect more like 200cc expelled and I guess the mixture we use will give us something in between these values - say 125cc. At the moment I have an airspace of about 200cc in the top of my header tank and this certainly gets compressed by about a factor of two as it warms up. Edited by - Colin Mill on 28 May 2008 15:59:45

Shall I do a bit of a sketch and pop it on my website so we can kick the idea about till we have something that looks right? Perhaps then we could get a few made for those interested in trying it.

Hi Johnty On mine I think the temperature sensor is in the main outflow from the head rather than in the bypass take-off tube but I'll have to double check.

A good point. After Johnty suggested the valve removal modification I was thinking that perhaps this would bring the temperature of the swirl pot up quickly if the pipe from the top of the head was plumbed into the pot. However, we could blank off the existing bypass outlet and have a rearward pointing 16mm outlet on the swirl pot from which the bypass could be taken so that the full flow went via the pot. I would like to keep the top of the pot as high as possible so I'm going to eye up what the nose-cone will allow. As far as I can see the tapping on the submarine section can be blanked off once we fit a swirl pot as the existing header gets relegated to an unpressurised expansion bottle. I was wondering if the expansion bottle should be a heavy PVC bladder (as per 1960's Fiat windscreen washer reservoir) as this would be light and have no air inside to dissolve in the reserve coolant. Edited by - Colin Mill on 28 May 2008 08:37:06

Yes, I'm sure that is a good modification and one I might do anyway as I think an airlock could get trapped in the head if that valve sticks shut. I'm not sure why Rover considered the valve necessary - perhaps it makes sense in the installation in Rover cars. At the moment I top the header tank up so the air space is so small that the expansion of the water in warming up puts this under significant compression. My reason for going for a Stant cap is that it is a known quantity with a known operating point and a good reliability record. It can also easily be visually checked for defects (perished seal rubber or broken spring). The Rover part may be OK but how can you tell if it's gone duff? Edited by - Colin Mill on 27 May 2008 22:38:40

This is quite interesting. I have for a while been contemplating changing the header tank arrangements as I think the existing header is rather hit and miss. I don't like the fact that the pressurisation of the system is delayed until the header tank contents comes up to temperature - the air space normally left in the top of the header means that very little pressurisation comes from the expansion of the water and significant pressurisation comes only from the vapour pressure over the hot liquid in the header tank. I wonder, for example how much the airflow through the engine compartment cools the header especially as there is little or no through flow of coolant in the header as the ball-valve at the head end of the pipe inhibits this unless there is gas in the head. The header seems to be heated by convection from the submarine section which is one of the coldest bits of the system *confused* What I plan to do is get a swirl pot like the one on this page but with the top fitted with a Stant cap like this.. I will then need to arrange an unpressurised overflow bottle (possibly the existing header tank with the top hose fitting taken to a vent pipe to the bottom of the engine compartment). I think this should allow the system to come up to pressure much quicker - with no air space under the cap it will tend to pressurise by water expansion. Edited by - Colin Mill on 27 May 2008 22:40:01

If you had a lifetime to spend on the job I guess you could use a small ball-ended cutter in a high speed rotary tool like a Dremel and grind away most of the inside part of the rivet - just have dust left inside the chassis 😬

An old trick (or at least one shown to me by an very old mechanic) for removing rivets was to drill till the rivet just starts to revolve and then slightly incline the drill (I'd guess 10 or 15 degrees). Because the drill and rivet are not aligned the drill continues to cut. Does a very neat job in my experience.

I'm with Oily - there may be any number of reasons why the foam does or does not break up in any given engine - it could be that different materials have been used for different batches of foam or that certain oil additives attack the foam. The critical things for me are:- a) No one has given me a good, detailed explanation of how the foam acts to prevent oil surge (and I don't see an obvious one myself) b) The causes for the break up have not been identified so you have no way of avoiding it in your engine.

Hi Darren Good one! I'll give that a go as soon as the morning coffee has sunk in enough for me to face my in tray 😬 Colin

Hi Darren For some reason I'm having difficulty emailing you regarding the line lock control circuit (replies just bounce??). If all else fails we will just have to start a thread about it 😬 Colin

Just one thought if you plan to do any more - with the braking forces being fairly uniformly distributed across the pads the maximum stress is nearest the hub and least near the edge so you can afford to take a higher proportion of the weight out near the edge than the hub.