Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Coolant Volume

KEEP IT SIMPLE....? I am guilty of rambling on quite a bit, though it seems best when trying to help others with overheating issues, to try to stick with the basics....?

First off, an apology to GoMoG... re the height of the expansion tank.... I suspect it may not be not critical in terms of an inch or two, either up or down, as it seems part of the expansion system design requires pressurised air to return the displaced coolant to the rad..? That being accepted...it seems logical that IF the level of the airspace in the expansion tank was mounted below the filler neck of the rad.... then I suspect there is a chance that during the transfer disturbance of hot coolant from the rad to the expansion tank, there may be a chance that air from the expansion tank might just find a way back into the engine.... air ever seeking to rise above water...?

That the heater matrix tends to be located higher than most components in the system, it would seem ideal if the lowest level of the airspace within the expansion tank was kept above the matrix and the pipework connected to it, then that would seem ideal...? I note posts on locating a manually operated air vent located on the pipework feeding the heater matrix, the route of which seems to be purposely extended to create the highest point in the system, which seems a simple enough solution for bleeding air..

As it seems to date that no one has discounted my thinking on the initial design process of the system being that air pressure created by the engine displacing coolant from the rad and into the expansion tank as the engine works towards normal operating temperature, and that as the engine cools when shut down that the process acts in reverse.... Then perhaps using no more than simple logic, I may have understood that part of the system design...? As ever I am happy to wait and be corrected as part of my educational process..

Not quite. As the coolant heats it expands and is less compressible than the gas (air). The pressure rises but the ar is compressed from o psig to say 15 psig i.e .1 atmosphere above atmospheric pressure.

If the vent cap on the expansion tank is below the fluid level in the rad then fluid will auto syphon out of the expansion tank if the vent cap opens assuming the rad is full of coolant of course.

Expansion tanks normally have marks to show a fluid level & then a head space.
You can see on Belle that the fluid level in the expansion tank is level with the top of the rad & then there is an air gap. I marked the line with tape because MMC reuse header tanks, in this case a Ford Fiesta and the marks on the tank are not relevant.

Many thanks for taking the time to reply John in a bid to enhance my understanding, which in Morgan terms is based upon my mid 80`s +8 and which differs from that fitted to your Morgan.

I am somewhat confused to think that although the expansion tank is exposed to whatever pressure might be applied within the system as the engine warms up causing the airspace within the tank to reduce and thus compressing the air up to a possible max as determined by the blow off point of the rad cap... That this increase in air pressure may not play any part in the return of the coolant to the rad, regardless of whatever height the tank might be at....?

Again with limited understanding I thought syphoning required some measure of initiation, and if the pressure cap is in place on the expansion tank providing sealing to to the system from atmosphere, it would seem syphon may be unlikely to occur..?

Again using nothing but my limited logic... I can imagine that there may be a possibility of some siphon occurring due to the effect of gravity on the coolant within the tube connecting the rad to the expansion tank, assuming the run of the tube is such that the end of the tube connected to the rad is higher than the end of the same tube connected to the expansion tank.... However for the syphon action to begin, it seems logical that the process might only begin if the pressure cap was removed or failed to seal the expansion tank and thus the whole cooling system as it is designed to....?

Even when cold and no pressure in the system as I understand it, with the pressure cap in place on the expansion tank and thus sealing it, I fail to understand as to how syphoning might occur.. I guess if one has fitted an expansion tank where the level within it can not be viewed without removal of the pressure cap, then dependant on the height of the tank mounting relative to the coolant level in the rad, some degree of syphoning could then occur..?

As for the tank it`s self, I suspect all that matters relative to it`s construction is that it can safely operate at internal pressures in excess of that which the rad cap is set to blow off at. The tanks internal volume is such that it can contain the amount of coolant expected to be forced into it as the engine rises to operating temperature. Also that the tank is designed to be capable of maintaining the amount of coolant at normal levels when cold. I also suspect that the positioning of the tube that links the tank to the rad is such that it may be near the bottom of the tank. Also that when the engine is up to normal running temps that there is enough airspace maintained above the coolant, and perhaps finally that the siting of the connection for the blow off tube is such that it directs whatever is expelled, in such a way as to avoid danger or damage to people or equipment..

While rambling on perhaps it may also be worth mentioning that the tube and clips connecting the rad to the expansion tank will be designed to operate at both the max temperatures and pressures expected to be created within the system...

As ever I am keen to learn where I might have got it wrong...

Of course all the bits are built to take 15 psig plus I would expect 30-50% more. The siphoning doesn't happen unless the vent opens.
When it does if the vent is below the level in the rad it will not just blow off air but suck through fluid till it closes.

John many thanks for being patient re my use of logic creating questions in my mind relative to the specific operation of the cooling system on my mid 80`s +8 , which not unusually would seem to be configured differently from that which is in place in your V6, despite the use of a remote tank in both our Morgan`s

It does indeed seem that the remote/expansion tank can be found in a few different Morgan`s and that as such it would seem that their operational function may differ in terms of what type of cap goes where, perhaps that the necks on both the rad and expansion tank are similar on some Morgans, it could perhaps be a simple matter to refit caps the caps in the wrong location during a rebuild...?

When you type of the vent opening in the pressure cap, apparently there may be two different types of vented cap as per the Jaguar web page I mentioned, one which is opened and venting and the other which is closed until vacuum within the system might suck the valve opened...?

It is my guess that a pressure cap of the type fitted to my +8 may not need to be a two way cap. The primary action being to blow off pressure at or around 15PSI, and a secondary action activated by any possible vacuum building up in the system as the coolant contracts back into the rad.... I suspect as the caps operate on my +8, the pressure created within the tank by the air compressed within it as the airspace having been reduced by expanding coolant, that same pressure will act upon the coolant to assist it to return to the radiator when the engine is shut down and begins cooling ...?

Alternatively, I presume the same dual action pressure cap as is fitted to my +8 could be fitted to a rad with a remote tank utilised as a recovery system, whereby the remote tank would have a vented cap open to atmosphere. Thus allowing any coolant displaced by the rad to expand into the tank above whatever pressure the rad cap is set to pass hot coolant at (likely much less than 15psi) and once things start to cool down the secondary and closed valve within the cap, will be caused to open by vacuum created as the coolant within the engine contracts...

Returning to thinking on my +8`s cap were it only a one way pressure cap and with a blanking cap in position on the rad (as fitted), it would function no differently than it appears to have done during my 20 year ownership....?

As ever open to suggestions of where I have misunderstood the function of MY +8`s system and where a dual functionality of the closed to atmosphere cap (as fitted) might be required...

Just passing the time thinking in type.

Yep some caps do prevent vacuum. I would suggest you call Rutters or BHM for help as they will have the bits.

With respect John V6, why would one want to prevent the beneficial effects of vacuum? I am very curious

On another unconnected note, I am Canadian and therefore have no patriotic urge to buy locally, aside from using the many machine shops unbridled by many legal liabilities and insurance regulations. Vast sparsely populated primary economies cannot afford such niceties. Though I buy most of my Morgan parts in the UK of course, my PRIMARY rule is to buy the most suited components for my hobby car, irrespective of cost from any place that produces them. Italian rad fans (SPAL), Mulberry rads, British engine blocks, and some American (the king of the world automobile aftermarket, safety thermostats, wiring products and so on. The smartest radiator caps are from the USA. I am an unabashed fan of Brands Hatch, but being in the UK, they are not supplied with the world's best rad caps, and certainly not Melvyn.

gmg

Thanks again for taking the time to reply John. Fortunately as I declaired near the outset of this discussion, my standard tune mid 80`s + 8 has not ever overheated even in one of the hotest days that Italy had experienced while touring there a number of years past. Fortunately I am currently not in need of replacing either of the caps on my old +8 at this time, but thanks for the suggestion of possible suppliers.

My thinking on contributing to this post was in the hope that my simplistic thinking might just help others to assess any possible issues they might be concerned about relative to possible overheating in their older Morgans, by encouraging discussion on the make-up and differences in design of cooling systems and components perhaps fitted to their Morgan, either correctly or incorrectly. All of which seems possible in the passage of time given it seems simple to imagine a pressure cap is just a pressure cap, when in fact it seems that there are indeed quite a few different types available which will fit on the filler neck of many a rad or expansion vessel.

Yeah, trying to keep it simple can require too many words from the likes of me... Sorry.

Oops... Seems GoMoG replied while I was typing mine... As I typed and as best I understand it the idea of a two way pressure cap that is designed to prevent vacuum build up and thus collapsing flexible hoses, which would seem to further complicate cooling when next fired up...?

It would seem in my old +8 there may be little or no need for that type of cap on my Morgan as the pressure build up in the expansion tank would seem to combat the chance of vacuum being formed in the system as the coolant is returned to the rad as it cools...?

I suspect the same two way closed type of cap as mine, IF fitted to the rad in a recovery system might perform to allow coolant to pass back through it though as I typed I also suspect that type of cap if used in that way would perhaps have a much lower blow off pressure than the cap on the remote tank...?

Yeah cooling Morgans of all types has ever been a hot topic.... (-:

You may be interested to know that my tweaked 4.8 EFI nor my UK tweaked 4.6 EFI have never overheated in the says type of days. Of course, they were altered by myself not to, despite double the bhp.
The only occasion I boiled over when I was using an engine identical to yours (save EFI) rather aggressively in the Dordogne on a day in 40C+. However, many EFI Plus 8s do overheat (along with Triumph Plus 4s). The goal of the community should be to find out why many do and ours don't. That would be of great interest to the 3.7 Roadster crowd and so many other post-carb LR Plus 8s. I have given that a lot of thought.

BTW, our 3.5 engines (all of them until 1993ish) had a design defect that encouraged blown head gaskets and were using tin rather than the later composite gaskets. That being said the 3.5s were more solid blocks than the later variants (though Morgans did not have enough load to be effected by the later block variants or the cracked block slipped liner plague that ended the engine).

Incidently, you are confirming the vital differences between carb'ed and EFI. In the case of your car, it is not simply lower bhp, as Weber 500 fitted engines can achieve almost the bhp of a L-Jet 3.5 according to Hardcastle's dyno testing and higher than stock Hotwires and GEMS. People often forget that the less efficient burn of a carb'ed car is NOT wasted. The engine uses the unburned fuel as for unintended cooling factor. That is why your car has a thermostat opening at the lower 82C. If I used a 82C thermostat, it would NOT effect my running temperature..it would merely take longer to get where the EFI system wants to be. The key here is that the stock Plus 8 cooling system of the mid-1980s could cool YOUR car but not a concurrently made EFI Plus 8, for more than a decade afterward.

That is what should be pinned down. We two, for very different reasons, are not having any issues. But we should help others. As you state: "Yeah cooling Morgans of all types has ever been a hot topic...." (-: This recently come into focus again with the appearance of well-reviewed Morgan aluminum radiators from China, appearing everywhere at 25-35% of the prices well-known suppliers. Sadly, like Morgan aftermarket rads, they copy the traditional designs that don't work well.


If you are properly using an expansion system, new caps are merely a question of how safe you want your system to be for the extra few pounds it costs. Inevitably, an expiring cap (spring or flanges) expresses itself in failure. I carry spare caps in all my Morgans.

gmg

Lorne here is what one supplier says
KAFTON UK

PRESURE RATING SPEFICATIONS SIZE

13 PSI (0.9 Kg/cm2)
16 PSI (1.1 Kg/cm2) SAE -J-164 (Reaffirmed FEB97) MINI CAP [For 43 mm dia. Filler Neck]
7 PSI (0.5 Kg/cm2)*



When the engine is started from cold conditions the temperature of coolant rises due to heating up the engine. Heat extracts from engine water jacket. As the temperature rises, the volume of coolant is expanding and positive pressure starts to take up. This goes on up to certain extent, which is prevented to avoid damages to the cooling system.

As the pressure exceeds , the set limit of system , pressure cap starts functioning and lower sealing discs is lifted releasing pressure and allowing the hot coolant to escape through the overflow tube provided in the fillerneck . If single sealing cap is there and no reservoir is in the system, then the coolant will be lost . However , if double sealing cap is there and the recovery reservoir is provided in the cooling system , then coolant escaped from overflow tube is collected in recovery reservoir and cooled down the temperature.

When the radiator is cooled, coolant inlet temperature reaches below boiling temperature , it contracts and the pressure inside the radiator reduces and reaches to negative pressure i.e vacuum is not broken , it damages the radiator and its hoses in extreme cases . The vacuum valve provided in the cap comes in operation and allows Air to enter into the radiator via overflow tube of fillerneck in case of single sealing , and coolant from recovery reservoir in case of double sealing and breaks the vacuum in the cooling system.


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