Cooling System Pressure

[red&black]

Has anyone measured the pressure at which the cooling system of a sprint runs please?
I mean the actual pressure in the system when at operating temperature-not the rating of the pressure cap.
Thank you.
James

[gmsclassics]

An interesting question with no straight answer.

I have a pressure gauge on the dashboard of my race car that measures pressure in the thermostat cover. Historically i have found that once up to normal running temp on the road, pressure can vary in the 5-9psi range. I suspect it could also depend on rpm (of the pump) and where the measurement is taken as I am sure there are areas of greater or lesser restriction. There also needs to be sufficient air in the header tank to cope with expansion as temperatures rise. As soon as all the air is compressed you will immediately get up to cap pressure. Hence if you overfill the system with coolant, some is lost via the cap.

Of course if the coolant boils, or even if there is localised boiling after a very hot engine is stopped, steam can cause a very rapid rise in pressure.

I have been suffering coolant loss (500ml per race) and am currently experimenting with a small header where the washer bottle usually is, a 13psi recovery cap leading to a 1.5L overflow bottle. The coolant system is full right to the top of the header (easy to bleed the sytem with this set up) so the system is always running at 13psi with fluid exiting to the overflow bottle and being sucked back as necessary. Time will tell if this works better.

Geoff

[red&black]

Thank you for your reply Geoff.
The background to me asking this question is as follows:
I have previously had the usual problems with head gasket failure causing coolant loss through the expansion tank,and having fixed this I like yourself have fitted a pressure gauge into the cooling system in the hope that it may give an early warning of any excess pressure in the system.
The gauge is plumbed into the hose between the expansion bottle and the thermostat housing,and the highest reading I have seen is approx 4 Psi when the engine has been run and then left to idle.Whilst the car is on the move the needle on the gauge barely registers.
I have just got round to finding and fixing a leak from the cooling system-this was coming from where the capillary tube for the electric fan thermostat entered the top hose on the thermostat housing. I found the leak by pressurizing the system with a pump and pressure gauge (engine cold),as it was impossible to find by running the engine and looking for leaks or water stains. I connected the pump to the hose from the expansion bottle to the thermostat housing,and now that the leak is fixed an indicated 20 Psi can be held indefinitely.
Whilst I had the pump handy,I decided to test the expansion bottle and pressure cap in the same way.The most I could get the bottle to hold was 4 Psi (the same pressure that my gauge has ever recorded with engine running),so I tried a new 13 Psi cap with exactly the same result.
The above made me ask myself the following questions:
1. Why are two 13 Psi caps venting at only 4 Psi?
2. Is the bottle causing a bad seal between itself and the cap? It is a new plastic bottle (ARH259 I believe).
3. If the bottle is faulty,would my best plan be to convert to the Volvo 850 bottle that several others have used?
4. Would the 22 Psi cap which I believe is fitted to the Volvo bottle be too high a pressure for our cars to safely run at-if indeed they create that much pressure when healthy?
5. How much pressure do our cooling systems create (my original question),and is 4 Psi enough?-after all,when using water the idea of the system being pressurized is to increase the point at which it boils.

I recall an article that may have been in Dolly Mixture which suggested that many pressure caps open below the pressure which is stamped on them.It suggested modification of the cap to create a more realistic opening pressure-I will try to find this and report back if anyone is interested.
I will see what else I can do in the mean time.
Thank you again

James

[Edin Dundee]

I use this:
http://www.bbclassics.co.uk/classic-car ... -caps.html

[sprint95m]

2. Is the bottle causing a bad seal between itself and the cap? It is a new plastic bottle (ARH259 I believe).
3. If the bottle is faulty,would my best plan be to convert to the Volvo 850 bottle that several others have used?
4. Would the 22 Psi cap which I believe is fitted to the Volvo bottle be too high a pressure for our cars to safely run at-if indeed they create that much pressure when healthy?

I can offer answers/observations on three of your questions James.

No.2 The plastic bottle is the weak link of the cooling system because of the poor sealing with the cap.
In a Dolly Mixture some time ago, Jod Clark wrote an article concerning this.

No.3 It was me who wrote about installing a Volvo 850 bottle.
This avoids No.2 and furthermore has a low level warning sensor which will (if the bottle is suitably positioned) provide a warning
BEFORE the level has dropped in the engine.

No.4 No, not in my experience. Doesn't the increased cap rating provide a bigger safety margin before the water boils....?

Since then I have converted to run on Evans Waterless Coolant (Power Cool 180, (the classic versions aren't really for a slant four)) which runs at atmospheric pressure,
so you don't even need a cap to be fitted! This reduces the strain on all components of the cooling system and also doesn't cause any internal corrosion.



In conclusion, if I was permitted only do one thing, I would choose to convert to EWC.




Hope this is useful food for thought,

Ian.

[red&black]

Thank you for your reply Ian.
I will try to find the Dolly Mixture article on expansion bottles.
I have found out two old plastic bottles and caps(I also have a brass one somewhere),and will do some testing on them when time and weather permit.I have a suspicion that poor sealing between bottle and cap may have been a problem from when the cars were new,and may possibly have contributed towards the reputation for overheating and poor reliability that they gained.
I am reminded of what was suggested when the Stag's cooling system was analysed on Channel 4's For The Love Of Cars. Apart from the fan viscous coupling breaking on a rolling road session,all performed as it should do with standard parts in good order.The reason for overheating on new Stags was suggested as being caused by them being filled with coolant too quickly on the production line,and thus creating air locks from day one.Whether this is true is open to discussion,but the point I am making is that if the cars were fit for purpose when new then they should work correctly with standard components.
I have been considering Evans coolant and the Volvo bottle for a while,but will try to make the cooling system work properly using standard parts first-I will report back with my findings.
My car came with a brass expansion bottle when I bought it,and although they may arguably be better than the plastic ones,I do not like the idea of not being able to see what is going on inside them without removing the cap-thus I changed to a brand new plastic one.

Thank you.

James

[sprint95m]

Regarding the metal v plastic original expansion bottles.....
Whilst you can indeed observe the coolant level within the plastic type, there is however a major snag....
If the cooling system springs a leak about the inlet manifold, the level will drop within the engine but NOT in the expansion bottle.
This happened on my 1850 when the thermostat housing bolts failed (it was actually the manifold that had lost its threads) but fortunately the hissing and staining
were easy to detect In the BL workshop manuals there is a warning about such an occurrence because the temperature gauge won't be affected.

I am reminded of what was suggested when the Stag's cooling system was analysed on Channel 4's For The Love Of Cars. Apart from the fan viscous coupling breaking on a rolling road session,all performed as it should do with standard parts in good order.

I saw that too and indeed enjoyed the whole series.
It wasn't mentioned in the programme but that car (along with the others that they sorted) was converted to Evans Waterless Coolant, Evans being one of the programme sponsors.



Anyhow James, if you PM me your email address I'll send you the articles from Dolly Mixture......





Ian.

[red&black]

Thank you once again Ian.
I would be interested to see the Dolly Mixture article and you will save me ages looking for it if you would be so kind to send it-thank you. I will PM you.
I have had some progress (I think) in as much as I have managed to get my new plastic bottle to vent at 13 Psi by using a modified pressure cap on it. This entailed taking the cap apart and lengthening it by adding some washers. When I have more time I will refill/bleed the system and run the engine to see what happens.
Evans coolant in the For The Love Of Cars Restorations? I didn't know that. My favourite one of the series was the Land Rover-I have a real soft spot for them despite their shortcomings.

Thanks again

James

[red&black]

A bit of an update on this.
Found a slight coolant leak from the seal where the capillary tube for the electric cooling fan thermostat enters the top radiator hose on the thermostat housing. Bulb on the end of the tube is now positioned here:


After adjusting the thermostat the fan comes on at 92 degrees C and goes off at 85 degrees C,so in my experience there is no need for the capillary tube to be immersed in coolant for it to function properly-does away with the problem of sealing around the tube.
Engine and all associated plumbing will now hold 20 Psi-no leaks.

Pressure tested the plastic expansion bottle which was found to hold only 4 Psi even with a brand new 13 Psi cap fitted. Several other bottles and caps tested with similar or lower results.

Drilled out the rivet holding an old cap together and reassembled it using a screw/nut and 2mm thickness of washers to lengthen the cap. This configuration held 13 Psi on a new plastic bottle when pressure tested.

Fitted an extra rubber seal onto an un-modified brand new cap ( a bit tricky,but can be done) and this cap opens at 11 Psi when fitted to the new bottle. This is not quite the 13 Psi which it should be,but it is much easier than splitting a cap and lengthening it with washers,and is much better than the 4 Psi at which it was opening originally. It also appears as standard externally.

Filled and bled the cooling system.
Pressure in the hose between thermostat housing and expansion bottle is around 3 Psi at normal operating temperature.
I am awaiting some dry weather to road test,but all seems well when stationary.

Hope this is of some use-many cars may be fitted with an expansion cap which is opening at an incorrect pressure due to poor sealing with the bottle if my experience is anything to go by-and I was using new parts....

Don't worry about the electric fan mountings in the picture by the way-it is properly mounted onto the radiator out of shot,and these are just some extra insurance.

James

[Edin Dundee]

I had leaking caps too - hence the Fah-Ler option a few posts above, although they don't look original.

[red&black]

I had leaking caps too - hence the Fah-Ler option a few posts above, although they don't look original.

Thank you Bill-I may buy one and pressure test it.

James