Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Coolant Volume

The “after” photo is what I had on my 2002 Plus 8. The black expansion tank where shown. 15psi cap on it and blank cap on the rad. The term “expansion tank” is very apt! It collects excess hot coolant to either feed back to the system when it cools or bleed it to a tube to drip away if in excess. By keeping this tank filled to the correct level it prevents air getting back into the system. That air is either trapped airlock expelled into the tank or fresh atmospheric air.

Hope you do not mind but as cooling issues ever seemed to be a hot topic (pun intended) on the various Morgan forums over the years, I thought to add my tuppence/two cents worth.. (-: More than happy to be corrected if I have made any mistakes..

I can well see that there is quite a bit of room for confusion given that the neck on the radiator of my mid 80`s +8 is identical to that on the expansion tank, thus the rad would take a "normal" pressure cap, whereas on my Mog, the pressure cap is fitted to the hard plastic expansion tank, and as already been explained the radiator is fitted with a blank cap, thus the flexible tube from the filler neck of the rad that connects to the bottom outlet of the expansion tank is free to transfer the coolant as it warms and expands, into the expansion tank.

It is the expansion tank that determines the allowable pressure within the system via the pressure cap setting (15lb on my +8) the top tube on the expansion tank is the overflow, which should only ever overflow relative to the pressure build up in the cooling system rising above 15lbs/sq inch..

On my +8 as can be seen in the pics the water level in the sturdy plastic expansion tank can be clearly seen through the material the tank is made of which is perhaps worth noting as the tank it`s self has moulded lettering with arrows indicating WATER LEVEL.... these arrows point to the lower ridge in the tank where it slims down, as if it were shaped to take a strap... If my description causes confusion I will try to grab a pic of the level markings.... On my Mog the level in the tank reaches those arrows from it`s present position only when at normal operating temp, which for my carb fed and standard tune mid 80`s+8 is 90Deg C

If filled to the indicated water level when cold, the excess is seemingly spat out during a trip, and on returning home with the engine up to temp the coolant id found sitting at the water level arrows, and once cooled returns to the level as can be seen in the pics....

I suspect the height of the expansion tank seems unlikely to be critical...? It would seem logical that as the engine heats and the coolant expands up the tube and into the expansion tank the pressure in the expansion tank will increase. As the coolant drops in temperature and contracts, it seems likely that the pressure built up in the tank by compressing the airspace above the coolant level in the tank, will then force the formally expanded and now contracting coolant, back along the tube and into the radiator.

I took a pic of both my rad pressure cap and blanking caps which I hope to provide a ling for below.

The thermostat opening temp is listed in a Rover 3.5 V8 manual as being 82Deg C (180Deg F)

Reluctant to type this.... But my Mog has not ever overheated, even when Mrs Luddite and I got way too hot while touring in a VERY hot Italy some years back.

Another point perhaps worth mentioning is that even rad caps with the same poundage can operate differently, as can be seen if you open the E type link below. I suspect the one with the small valve that is open to atmosphere when there is no pressure in the system, does so in order prevent vacuum build up being created by coolant contracting and thus avoids the rubber coolant hoses collapsing.

Radiator Caps Explained (coolcatcorp.com)

https://www.tm-img.com/image/SvUAn
https://www.tm-img.com/image/SvBu4

Correct. Well spotted. It is merely that this placement is no longer ideal as the earlier one, another concession to modernization forced upon the MMC. That is a very hot place to put a expansion/recovery tank. It is a manufacturer/ government cultivated illusion that internal combustion engines have changed significantly over the last 120 years. Still a varying number of pistons driven by air/petroleum/sparks producing heat et al.. (shrug) Far more driver aids now tho, along with regulation-driven weight.

Yes..as it is not only the reservoir filled but the filled hose length between tank and radiator, which was muchly shortened by 2002. Air had to go a much longer way before they abandoned the Hotwire (3.9s) configuration. The less coolant in a system, the harder it is to cool or be effective. (duh). Same with motor oil.

I find all this stuff intellectually intriguing!! One can trace the route of all technological history, good and bad, by merely understanding its effect on trad Morgans.

I have no wish to soapbox an universal preference for expansion versus recovery systems. However, there are some cars/engines that are better suited to one than the other.

gmg

No problem. Fire away!


Yes I had one of those myself..(below) Remember my first Plus 8 was made just a few months before yours. Sadly, it melted in the aftermatch of our 2002 accident. I first switch to its copy in black metal and then to large prettier tanks as time went on. Not sure why the switch from plastic to black metal, though the later is said to release heat much more efficiently. LR/Rover stuck with black metal of different (lager sized tanks) after that.


Mine as well. Plus 8 water pumps (until the crank driven GEMS) should not take much more. And the engine innards are not set up for more.


Convenient, though on a proper system, the water always returns to the same place unless one mistakenly under fills.


Here is the crux of it. We are addressing different things. Though my first car was made earlier than yours, it was an EFI, not carb'ed. All EFIs are required to run hotter, for a more efficient, reg-compliant burn. The fine spray mightily increases the bhp and therefore the need and production for the heat. All Morgan LR/River EFIs from the optional (L-Jet) ones in 1984 to the last of the stock line in 2004 (GEMS) have a thermostats that begin to open at 88C and should have rad fan switch ranges 6C+ higher than yours. Few are properly set up. (And sadly, owners are sold whatever replacements that are close to hand from non-savvy suppliers.)

However, the MMC did not alter their Plus 8 cooling system from your carb system for 1another 5 years, creating a generation of worried owners and lots of radiator aftermarket joy. (wryly) Bill Beck only began to work on that with GEMS Plus 8s, when he installed SPAL fans in 1999 IIRC.


It is critical. As the expansion tank system and the hose to it is part of the entire system, as you well understand, it makes no sense to try to fill from the bottom up.


That's great! But you have a significant advantage from the EFI crowd. EFIs of the same era and later have the same cooling system and components as you, along with a higher opening thermostat and rad fan. Keeps their owners worried. I boiled over once, where spirited driving in Dordogne on a hot day, while I still had the original 3.5, brought this common fault into my life. https://www.gomog.com/headgaskets.html Actually, I wouldn't change a thing of that day. I swapped in a tuned 4.6 on my return to England. I have a picture of the gasket.

gmg

It looks like my 1993 Plus 8 has a pressure cap on both the radiator and the expansion tank. Not sure what pressure the relief valve is set to (there is a number 13 stamped to the cap so maybe 13 psi). From the advice of this group it sounds like I should change the radiator cap to just a standard shut cap and allow the pressure relief to occur on the expansion tank side. Is there any downside in keeping the current configuration?

https://flic.kr/p/2po4hBf
https://flic.kr/p/2po2zDH
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https://flic.kr/p/2pnWSLV

Thanks.
D

The cap on the rad will/ could vent and normally the expansion tank is higher so then you will lose fluid from the rad. The design is that the expansion tank allows for thermal expansion and vents air not fluid. The cap on the should be non venting.

GoMoG, forgive me if I might suggest that I think we may be discussing the same thing...differently... ? (-:

I am with you on the slightly different operating temperatures of EFI engines compared to that of my old carb fed lump.

EFI seemed a logical step to reduce emissions and I think the changes in design managed to do so by a number of means, perhaps primarily by weakening the mixture more accurately than a carb could, in terms of adjustment relative to expectations of variations in engine loading..? bringing the term lean burn into the engine description dictionary...?

The first time I drove in convoy with Colin (AKA Spanner Juggler), in his then new EFI +8, I was aware at every traffic stop that his rad fan was constantly running, whereas mine was not, which made me aware of the lean burn aspect of evolution in engine development...?

Expansion tank location.... I can well understand there could be reasons I am not aware of, whereby the expansion tank might benefit from a different location, however given my understanding of the possible operation of the system, gravity would seem perhaps not to be the primary force involved in returning coolant which has been forced into the "expansion" tank, to then return to the rad as things cool back down..?

If I might explain my thinking.... On my +8, the expansion tank has a clearly defined water level, indicated by text and a couple of arrows.

The indicated water level, if adhered to, would equate to the tank never being more than under half full..?

With the tank never more than half full, would seem to suggest that the system designers required that there be an air space maintained within the tank..?

The requirement for an air space...? Apparently it may be the case that water can not be compressed, whereas air can, thus as the coolant is forced into the tank as the engine temperature rises, it compresses the air space within the tank, and dependant upon variables, that pressure could reach up to a max of just under 15lbs/sq inch without issue. 15lbs/sq inch being the release pressure of the pressure cap...?

With however many lbs/sq inch of pressure built up in the tank by the expansion in the system, my guess is the air pressure rise in the expansion tank would be enough to push the water back into the rad as the engine cools, even if the tank was lower than the filler neck of the rad....?

As for how low a tank might be mounted, I guess one might get involved in all sorts of calculations perhaps even contemplating the possible effects of vacuum etc.etc.etc., but then this is a Morgan and I suspect that although quite a few scientists and very smart folk might own a Morgan, I doubt they would have bought into the idea of Morgan ownership in search of engineering perfection...? (-:

As ever more than happy to be corrected if my logic is flawed.... I have been wrong before..(-:

Yes. That seems to be the groups advice. But let me give you details.
Any manufactured amount of pressure is the one to follow..even when their advice is found to be wrong in many areas over time. They make the engines. They do not use them for millions of miles as we do. I have Workshop manuals from the Buick era and it is surprising how their advice changes as they learn from the field.
David, the higher the pressure of the coolant (determined by the pressure cap) the lower the chance of a coolant boiling, assuming everything else is as it should be. On the other hand, the higher the pressure, the more the water pump has to work and more the coolant fitting and connections have to be leak tight. So both lower and higher than 15psi is not advisable, but if absolutely necessary go to 16 psi, not 13psi. Altitude and coolant-to-water mixture are also KEY. Here is a example. (I will find a better one including 15psi and altitude for gomog. https://cdn.shopify.com/s/files/1/0...ressure_Chart_1024x1024.jpg?v=1642460070 You will notice that 4 psi makes a difference in boiling points. In hot Texas you are more like to find boiling over with a too low pressure cap. (13 psi( tan a correct one.)
Excuse my pedantic explanations but after 30 years, I loathe telling people an answer without their understanding what's behind it. It is how I prefer to be treated. We are all merely amateur hobbyists, but not unintelligent. IN SHORT.

1. Put a blanking cap on your rad.

2. Put a pressure cap on your expansion tank, which MUST be higher than the top of the rad. (Trust me) And in fact, it already is, right from the Morgan Works 30 years ago!

3. One other codicil. You are in the USA where it is easy to buy a safety rad pressure cap. In Texas, there are now as common and the same price as the older less safe ones used 30 years ago. The reason is simple. We do not always tighten the caps fully. Additionally Morgan vibration can loosen them. At best, that will lower your pressure and protection. At worst, well....use your imagination. A safety pressure cap for you is a nil extra expenditure or hassle to avoid this. These are caps that have a small lever that can only be shut when the cap is fully seated and make the caps vibration proof. Pick one up on ebay. https://www.ebay.com/itm/155220098426 I chose an expensive polished stainless one for a Mini Copper. I am community-infamous for my weakness for polished metal.

gmg

It is the pressure differential the pump has to work against not the absolute pressure in the sytem. So if the pressure drop due to mechanical resistance is 1 bar say at 20c coolant temp it will pretty much be 1 bar at 100c whist the pressure of the entire system rises. It is pressurised to stop the coolant boiling & to stop it also cavitating at the pump.

Fully agree that though for seals etc the pressure is a risk factor in failure.

The cooling system is pressurised to raise the boiling point of the coolant. This is to prevent the evaporating coolant cause air to form in the circuit. A car engine is designed to run at a desirable temperature. To maintain this the system must be designed to reach equilibrium within an acceptable controllable range. Hence a radiator’s heat exchange capability is set to do this, in conjunction with airflow through it. Add in other complexities of of thermostats to manage warming up, temperature controlled fans to cope with extra heat on some occasions ( stuck in traffic, extended higher speeds) coolant volume materials used in the engine, and systems etc . The use of a pressure cap means this boiling point is raised. Most cars use 15psi caps but others might not.
A pressure cooker works using this BP elevation to increase the temperature to speed up cooking. Likewise, mountainous areas that are at lower air pressure due to altitude have a lower BP for cooking in water. A liquid boils when its vapour pressure equals that of the atmospheric vapour pressure. At altitude the vapour pressure is lower so water boils at a lower temp.
In the opposite direction, an antifreeze solution freezes at lower temperature than pure water.
It’s possible to calculate both effects fairly simply but I forget the formulae. I left education many years ago but the physics, chemistry, fuel tech was fun (modtly!)