Wow, quite high pressures! Many thanks.
R12 era expansion tank cap pressure rating question
- Thread starter JohnW
- Start date
The higher the pressure the higher the boiling point. Simple.
Old British rubbish probably at around 5-6 psi max in the 60's Renault went into double figure with the 4 and 8 and never looked back. They are very reliable as long as properly filled and bled and all the parts are in good order. The only time I could think one would vent is if the head gasket went to the water jacket. I actually had this happen once, but managed the 250 mile drive home by keeping the throttle pressing to a minimum and stopping every 30 miles to vent off the pressure. it never blew off yet. Did make the hoses feel like basketballs though.
Old British rubbish probably at around 5-6 psi max in the 60's Renault went into double figure with the 4 and 8 and never looked back. They are very reliable as long as properly filled and bled and all the parts are in good order. The only time I could think one would vent is if the head gasket went to the water jacket. I actually had this happen once, but managed the 250 mile drive home by keeping the throttle pressing to a minimum and stopping every 30 miles to vent off the pressure. it never blew off yet. Did make the hoses feel like basketballs though.
I seem to remember reading on the plastic bottle caps that if they had discharged they were to be replaced.... Was in an old workshop manual I'm sure.
New plastic bottles even supposed oe spec about half thickness of the originals. used to have loads. can't find one now.
New plastic bottles even supposed oe spec about half thickness of the originals. used to have loads. can't find one now.
250 miles can seem like a long way... Well done. The only time in 50 years that I had an overheating problem in the R8 was a very small head gasket leak due to a warped R1130 block. Had it decked and it warped again a few years later. Boat anchor at that stage. The hoses have always been pretty good too. Thanks again for the information.
I have one old spare. Nice and thick. The optimist in me says they are using stronger plastic but that might be Pollyanna territory.
Well, live and learn. I set up a temporary test rig to see which of my little collection of pressure caps actually work.
The only one that holds pressure is the brand new one. It is blue, starts to leak at 140 kPa (1.4 bar, 1400 millibars or 20 psi) and holds around 120 kPa.
The others ALL leak down to low pressures, so are completely useless in the 'pressurising the coolant system' function. Heaven knows for how long I have been running the R8 with an atmospheric cooling system just like the 4CV. THat leads me to "does it matter that much" for my sort of driving? No problems in decades... I'm not sure that I'm game to run the R8 at 20 psi in the old money.
There's an old adage in my field of underground water resources exploration and management: you cannot manage what you cannot measure. Some truth there folks.
All comments welcome.
The only one that holds pressure is the brand new one. It is blue, starts to leak at 140 kPa (1.4 bar, 1400 millibars or 20 psi) and holds around 120 kPa.
The others ALL leak down to low pressures, so are completely useless in the 'pressurising the coolant system' function. Heaven knows for how long I have been running the R8 with an atmospheric cooling system just like the 4CV. THat leads me to "does it matter that much" for my sort of driving? No problems in decades... I'm not sure that I'm game to run the R8 at 20 psi in the old money.
There's an old adage in my field of underground water resources exploration and management: you cannot manage what you cannot measure. Some truth there folks.
All comments welcome.
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I love the test rig John.
You said that your engine temps are mostly around 85 to 90 deg C, the pressurised cooling system only comes into its own when you are running temps up near 100 deg C.
Thanks Col. You should see my oil pump rig - and attached is my 4CV water pump delivery rate test setup!
Yes, I've been thinking that way for years but haven't discussed the theory with anyone. I just couldn't agree that the system ever worked at pressure! You have to get some boiling in the head to get gas to increase pressures up the cap relief value to stop the boiling, if the reservoir is partly air-filled. The change in volume in the reservoir from coolant expansion gives at most, best estimate, 10% increase in system pressure above atmospheric (1-2 cm coolant level rise and Boyle's Law). So my pressure cap not working at all just doesn't matter.
The lower pressure systems seem to have radiator caps on the radiator itself, so there is no air to cushion the coolant expansion. That's the 3-4 psi territory.
Even with an 82 or 83 degree thermostat, the temperature straight out of the head struggles to exceed 80 degrees except when it is nearer 40 degrees ambient. Then it gets up to 90 or a wee bit more. I have a 3-row core and a 6-blade fan, but the old 2-row core and 4-blade fan was no different.
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I didn't notice the Le Mans poster was to busy checking out your test rig, hope its laminated, it wouldn't last in my shed if it wasn't would be covered in all sorts of debris.
That is an awesome poster, would even be worth a little money now, looks in good condition too.
The pressure comes from the expanding water. heat 23 gallons of water to 60 deg Celsius and you've got 24 gallons. That's why the bottle level changes hot to cold. What you need to take into account is that the heat on the parts is not uniform. This means your temp readings are indications only of the coolant surrounding the sender. This is why loss of coolant is such a problem the gauge will start to drop as the motor starts to cook. As an example Liz's old R8 with 150 hp and the standard cooling system would firm up the hoses when fully hot. My G with at least 50% more coolant in the system and much more pipework which was rigid, copper front to back. This would raise the bottle level another 3/4inch and make the hoses twice as firm. This is one way to make sure everything is good, there should be a firming up of the hoses when hot. It is always the same after some time and several different scenarios you know how your car will behave in a given situation. I had to change antifreeze brand once and this resulted in the fans cutting in on about lap 8 on a hot day, which had convinced me that something was wrong. After some checking and experimenting I reverted to my original brand and the problem went away, revealing my usual brand had a better rate of heat transfer, a quality that cannot be undervalued in a coolant.
In the dim and distant past I used to put a little of the unthickened foaming solution we used at work (for leak detection) in old tired heating systems, as it quietened them down and improved the heat transfer rates which was what was reducing the noise Kettling in the heat exchangers.
Nowadays there are many system inhibitors that can be added which do the same job, they are more important as the waterways are much smaller to give greater heating surface for any given size. I am luck to live in an area of excellent water quality, where scaling up of water heating appliances is not common at all. From memory about a half millimetre of scale build up decreases the rate of heat transfer by about 40 percent, a sobering thought if you live in a hard water area.
Just put the high pressure cap on John, you won't notice a difference in day to day use.
In the dim and distant past I used to put a little of the unthickened foaming solution we used at work (for leak detection) in old tired heating systems, as it quietened them down and improved the heat transfer rates which was what was reducing the noise Kettling in the heat exchangers.
Nowadays there are many system inhibitors that can be added which do the same job, they are more important as the waterways are much smaller to give greater heating surface for any given size. I am luck to live in an area of excellent water quality, where scaling up of water heating appliances is not common at all. From memory about a half millimetre of scale build up decreases the rate of heat transfer by about 40 percent, a sobering thought if you live in a hard water area.
Just put the high pressure cap on John, you won't notice a difference in day to day use.
Was on eBay of course
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My thinking is that having some pressure improves the heat transfer, whether that be by slight increase in density or being pushed into the localised 'hot' pockets surrounding the piston sleeves.
The least antifreeze added, the better the cooling. This is from a doc I once archived.
..the addition of ethylene glycol increases the density and viscosity, but decreases
the thermal conductivity and heat capacity when compared with pure water. It should be
expected that a 50 volume percent mixture will yield more pressure drop and require a
higher flow rate to achieve the same cooling effect as that of pure water.
Should be easy to find another brown valve to test which I believe from renault manuals to be 1.2bar (17psi)
I did see a reference that a 0.8bar white valve was used on a Trafic but can't find part number.
Franzoze reckon the brown to be 1.4bar, the green to be 1.2bar and a black to be 1.0bar, which probably makes the black valve the best option for your R8, and I have a suspicion it may improve your hot start percolation.....
Thanks for that! No-one has yet accused me of over-thinking this but it might be fair to.
I seem to recall that Frans runs a pressure sensor on his cooling system so there's a red light if it leaks and pressure reduces during a race. I'm running a standard Castrol glycol mix (less heat transfer than pure water I know) and mostly the car over-cools, just as the 4CV does. The expanding water raises the level in the reservoir by about 2 cm maximum, which hardly changes the system pressure (Boyles Law) since there is such a large air volume above the guide marks. It should still firm up the hoses a bit though. I was looking at my Scenic to check the cap didn't fit (it didn't of course) and it has a tiny air volume in comparison. I'm sure you are right and I'll fit the one cap that I now know works. As for the others, I might as well stuff a handkerchief in the hole!! I could put more coolant in the reservoir of course, and that would compress the air more proportionally and raise the hot running pressure.
That 40% number doesn't surprise me (scarey number though). I hadn't seen actually numbers before. Growing up in Adelaide teaches the use of rainwater or distilled water in cooling systems. Renault head corrosion there in the 1950s and 1960s there was horrendous, before the R4 arrived and coolant with it. I have a drum of 'distilled water' collected carefully as the condensate from our air conditioner.
Some of the competition guys here seem to use the Redline "Water Wetta" to improve heat transfer. Out of interest, do you know it? It's supposed to lower surface tension. For my money glycol does that already (if it can get out, it will!!) although of course it does reduce heat transfer. I was very pleased to see absolutely no corrosion inside when I changed my water pump after 36 years recently.
My temp sender was originally a 1970s Smiths unit that fits in the hose but it died in the end and there is a new sensor in the Smith's hose fitting now, with a matched gauge, just above the thermostat. 'Above' is the key word there as you have said. I must double check that the warning light switch on the head actually works! My old 16TS had the gauge sender bolted onto the head, and boy it responded quickly to coolant loss.
Thanks for taking the trouble to respond to this. Much appreciated. Here's the car in its favourite habitat (well, mine anyway). It's an old 19th century woolshed near the Darling River at Menindee, NSW, on a trip across the country to a 4CV Muster. 9,000 km, that trip. No problems.
Thanks for those Alex. I have green as 1 bar from somewhere else, but hadn't thought to check Der Franzose. My blue one is definitely 1.4 bar. I have a white valve (black body) as 0.7 bar for a Megane. Mind you if these things work with a =/-10% error range I'd be surprised.
I think the pressure, generated by coolant expansion, serves only to increase the boiling point (the density will be lower not higher, since it has expanded), as Steve said. Has to be a good think with respect to the risk of localised boiling that might occur without symptoms. I agree re glycol but would add that it also increases the boiling point relative to pure water. I certainly don't need anti-freeze in Perth!!
It's an interesting discussion and I'm grateful to all who have added their two bob's worth.