R12 era expansion tank cap pressure rating question

JohnW

JohnW

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I thought I'd ask this one with a wide audience. I have an R12 plastic expansion tank in the R8, with its orginal BLACK cap. My spare cap is GREEN, like our Citroen CX. They are Bailly Comte brand from Lyon. These tanks came in various cars with various pressure ratings. My spare (green) seems to be rated at 1 bar. I don't know what pressure rating applies to the black one. They came in blue as well, and similar later caps came in white on black and black on white.

Does anyone know what pressure ratings apply to the different caps? I've not had much luck looking on line. I want to replace the very old cap on the R8 but am not sure what pressure to use or, indeed, whether it really matters.

All comments most welcome! Thanks in advance.
 
That is a good question John, and know doubt will spark a great conversation.

I have had a look here on all the expansion chamber bottles, both plastic and glass and I can't see any pressure rating.

I thought they were around 7 Lb (0.5 Bar) but could be wrong.

I'm not sure what pressure the cooling system is designed to work at, the only thing I can think of by putting on a higher than designed cap is you run the risk of bursting the radiator or heater core
 
In the late ‘70’s and in my youth - I cooked my overloaded round headlight R10 on the hills up the western highway toward Ballarat - the graveyard of many a RER I suspect. The more it struggled to get up the hills, the harder I pushed it.

As the pistons started melting into the head- I suspect what little compression was left started to pump into the cooling system - because suddenly the glass bottle exploded with huge bang and copious amounts of steam. I guess pressure was building faster than the relief valve could release it - must have been pretty intense to break the not insubstantial glass bottle.

From that day on, I installed a temp gauge on any RER acquisition and learned to treat my poor little Renaults with a bit more kindness and respect.

So my response is:
  1. I don’t know what the pressure rating of the cap is/was.
  2. The ultimate pressure relief valve seems to be the bottle itself, which will let go long before the radiator shits itself!
 
COL said:
That is a good question John, and know doubt will spark a great conversation.

I have had a look here on all the expansion chamber bottles, both plastic and glass and I can't see any pressure rating.

I thought they were around 7 Lb (0.5 Bar) but could be wrong.

I'm not sure what pressure the cooling system is designed to work at, the only thing I can think of by putting on a higher than designed cap is you run the risk of bursting the radiator or heater core
Click to expand...
Hope so! My recollection is 4 psi, about 0.2-0.3 bar. I bar = 1 atmosphere = 15.4 psi if I recall.

The blue cap is 1 bar. The black cap came with the bottle 35 years ago so can't be excessive. It's just that it is 40 years old... I could put a pressure gauge on the reservoir but that is maybe excessive...
 
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Fireblade said:
In the late ‘70’s and in my youth - I cooked my overloaded round headlight R10 on the hills up the western highway toward Ballarat - the graveyard of many a RER I suspect. The more it struggled to get up the hills, the harder I pushed it.

As the pistons started melting into the head- I suspect what little compression was left started to pump into the cooling system - because suddenly the glass bottle exploded with huge bang and copious amounts of steam. I guess pressure was building faster than the relief valve could release it - must have been pretty intense to break the not insubstantial glass bottle.

From that day on, I installed a temp gauge on any RER acquisition and learned to treat my poor little Renaults with a bit more kindness and respect.

So my response is:
  1. I don’t know what the pressure rating of the cap is/was.
  2. The ultimate pressure relief valve seems to be the bottle itself, which will let go long before the radiator shits itself!
Click to expand...
Ouch. The glass bottles did explode from time to time, usually when the little pressure relief valve jammed shut. Earlier cars had a brass tank that (a) cracked in the end and (b) didn't allow you to see the level. So I fitted an R12 plastic bottle when my brass one failed. And yes, I fitted a temperature gauge about 50 years ago - electric with a sensor in the top hose.

Thanks.
 
Fireblade said:
suddenly the glass bottle exploded with huge bang and copious amounts of steam.
Click to expand...
Happened to me on a 40C day waiting in traffic in a (hot cammed) 15.
A lot of steam, very dramatic!

And yea as you say its going to go before the radiator goes. but maybe the radiator cap should be less bars than an exploding glass bottle needs?
 
Seem to think they are all in the range of about 0.9 - 1.2 bar
Renault used very high coolant pressures compared to their contemporaries at the time. This is to prevent localised boiling at the liner bases.
It will generate whatever pressure it generates (water expands 1/23rd when heated) so dependant on temp and volume in system.
Personally I would go with the highest rated cap, as you live in a hot place, as long as it's all in good condition it won't be an issue.
The issue with localised boiling is you don't know it is happening, as the temp sender only gives the temp of the coolant it is touching, the steam pockets generated by hotspots do not conduct heat and lead to metal loss at the base of the liners and block. Something we have all seen stripping old engines.
 
dauphproto said:
Seem to think they are all in the range of about 0.9 - 1.2 bar
Renault used very high coolant pressures compared to their contemporaries at the time. This is to prevent localised boiling at the liner bases.
It will generate whatever pressure it generates (water expands 1/23rd when heated) so dependant on temp and volume in system.
Personally I would go with the highest rated cap, as you live in a hot place, as long as it's all in good condition it won't be an issue.
The issue with localised boiling is you don't know it is happening, as the temp sender only gives the temp of the coolant it is touching, the steam pockets generated by hotspots do not conduct heat and lead to metal loss at the base of the liners and block. Something we have all seen stripping old engines.
Click to expand...
Thanks very much for that information. One of them, green knob on white screw base is 1 bar. Yes, localised boiling is indeed my concern. The glycol based coolants boil, as best as I could estimate with some Peugeot coolant, at 107 degrees at atmospheric pressure. Happily, my R8 sits around 80 degrees most of the time with an 82 degree (approx) thermostat. If the temperature nudges 40, which I reckon is hot, the gauge temperature comes up to a wee bit over 90. I built the engine in 1988, at least 150,000 km ago, and no symptoms of corrosion. I changed teh water pump the other week, after 36 years, and all was clean as a whistle as far as I see into the head.

I have one brand new genuine blue cap (spare for my Citroen CX), a second used blue one and a couple of serviceable (I think) black ones. We certainly suffer from the quality of some repro items! The newer Megane caps do not fit.

If I can actually find any proper information I'll post it here.
 
Last edited:
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Forgot, looking on Ebay France for Bailly Comte screw caps, the Clio/Twingo/R5 ones look the same and Calorstat make that size too, by the look of it.

www.ebay.fr

Screw Lid Cap BAILLY COMTE Expansion Tank Fits Renault Clio Twingo Peugeot 205 | eBay

Les meilleures offres pour Screw Lid Cap BAILLY COMTE Expansion Tank Fits Renault Clio Twingo Peugeot 205 sont sur eBay ✓ Comparez les prix et les spécificités des produits neufs et d'occasion ✓ Pleins d'articles en livraison gratuite!
www.ebay.fr
 
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JohnW said:
Forgot, looking on Ebay France for Bailly Comte screw caps, the Clio/Twingo/R5 ones look the same and Calorstat make that size too, by the look of it.

www.ebay.fr

Screw Lid Cap BAILLY COMTE Expansion Tank Fits Renault Clio Twingo Peugeot 205 | eBay

Les meilleures offres pour Screw Lid Cap BAILLY COMTE Expansion Tank Fits Renault Clio Twingo Peugeot 205 sont sur eBay ✓ Comparez les prix et les spécificités des produits neufs et d'occasion ✓ Pleins d'articles en livraison gratuite!
www.ebay.fr
Click to expand...
That is the same cap that is on my Alpine A110 except it has F7 instead of J8 on it, not sure what the alpha numeric mean.
 
COL said:
That is the same cap that is on my Alpine A110 except it has F7 instead of J8 on it, not sure what the alpha numeric mean.
Click to expand...
My R16 has the metal expansion bottle valve (glass bottle) with the number 815 stamped on it. This according to the manual equals 815 millibars or 0.815 bar. The test to see if the valve is working is to pump the pressure up to 0.9 bar (13psi) and it should then return to the setting marked on the valve, with a tolerance of + or - 0.1 bar.
 
Antoine said:
My R16 has the metal expansion bottle valve (glass bottle) with the number 815 stamped on it. This according to the manual equals 815 millibars or 0.815 bar. The test to see if the valve is working is to pump the pressure up to 0.9 bar (13psi) and it should then return to the setting marked on the valve, with a tolerance of + or - 0.1 bar.
Click to expand...
I also have a glass bottle with metal valve on my Renault R12 Wagon. I seen 815 stamped on it but did not know what that number referred to. With your information Antoine that number now makes sense, so I have learned something today. I was going to look in repair manuals but have not yet got around to it.
 
Glass Bottles are a waste of time !!!
The rubber valve seal eventually sticks fast to the stainless housing and bottle blows or hose bursts. They are serviceable but need proper rivets to put the top housing back on the base. I now just throw them in the bin. And replace with a plastic bottle.

Dauphproto is correct, Renault Spec, but seems that any make needs to be tested before blow off pressure can be determined. The top can be popped of the top of Renault type, and cleaned inside, many aftermarket are sealed/glued.

Renault test tool is a bicycle pump on the radiator cap, and a gauge on a T piece.

Ray
 
Antoine said:
My R16 has the metal expansion bottle valve (glass bottle) with the number 815 stamped on it. This according to the manual equals 815 millibars or 0.815 bar. The test to see if the valve is working is to pump the pressure up to 0.9 bar (13psi) and it should then return to the setting marked on the valve, with a tolerance of + or - 0.1 bar.
Click to expand...

Antoine is correct, same test applies to R4

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Antoine said:
My R16 has the metal expansion bottle valve (glass bottle) with the number 815 stamped on it. This according to the manual equals 815 millibars or 0.815 bar. The test to see if the valve is working is to pump the pressure up to 0.9 bar (13psi) and it should then return to the setting marked on the valve, with a tolerance of + or - 0.1 bar.
Click to expand...
That's very interesting and useful. Thanks so much.
 
geckoeng said:
Glass Bottles are a waste of time !!!
The rubber valve seal eventually sticks fast to the stainless housing and bottle blows or hose bursts. They are serviceable but need proper rivets to put the top housing back on the base. I now just throw them in the bin. And replace with a plastic bottle.

Dauphproto is correct, Renault Spec, but seems that any make needs to be tested before blow off pressure can be determined. The top can be popped of the top of Renault type, and cleaned inside, many aftermarket are sealed/glued.

Renault test tool is a bicycle pump on the radiator cap, and a gauge on a T piece.

Ray
Click to expand...
Yes, that's the way. I have a spare bottle. Get appropriate scale pressure gauge and make up test rig. Thanks Ray. No why didn't I think of that in the first place. Nice little project. I put the plastic bottle on a good 35 years ago!
 
JohnW said:
Very useful thanks. These are quite high pressures, as Mr Dauphproto said. I can't work out a similar pressure rating for the screw on caps for the later, polythene bottles.
Click to expand...
I recall 13psi radiator caps being the norm for Holdens

early Clio, R5, R19 and R25 expansion bottles
7700805031 Dark Brown Plastic 1.2 bar
7700805032 Pale Blue Plastic 1.6 bar

Haven't seen data for black as yet.
 
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