Talk Morgan Forums Thread Like Summary - Coolant Volume

I have recently flushed the cooling system on my Plus 8 and have refilled with coolant. I filled it up until I could see the fluid at the top of the radiator then ran the engine for 15 minutes then topped up again. It appears that the level is still adjusting and I keep topping it up since the level drops and is not visible in the top of the radiator (no fluid is seen in the expansion tank yet - the line to it is clear). So far I have added ~6 litres of fluid. There are no leaks in the system and I am sure there are no leaks of coolant into the engine since the oil seen at the dip stick is still clear and bright.

Maybe it just takes a while to get all the air out. Maybe a water wetter would have helped. Appreciate any insight from the group.

Thanks,
David

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.

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!)

David,

I'm sure this is just the coolant gradually filling various areas of the system which have airlocked. My 1993 +8 does exactly the same thing, and it can take quite a few hot/cold cycles before coolant remains in the expansion tank on cooling down. This is especially so if the "heater" (a euphemism if there ever was one) has drained down. I've never tried a water wetter, but I'm sure that someone on here will be along soon to describe their experience with it.

Dave

Plus 8s were a right nuisance filling with coolant when they first appeared. They were using the first Rover V8s that had a "teapot filler" suspended on the top hose between the rad and the engine. Made quite a mess.They would tell the owners to jack the rear of their car to fill the radiator! Air in the cooling system was inevitable. The bubbles in the system were so large they could even push the coolant away from the coolant temperature sender at the top of the engine. The resultant readings would scare everyone. I occasionally muse wonder whether that is why the MMC placed the rad fan switch at the bottom of the radiator when the temperature sender we read is at the top! Eventually they recalled all UK Plus 8s and that was end of the teapots. I have a picture of the Pickersleigh pile of them somewheres.

Your coolant capacity according to your Manual, is 9 liters. But it is rare you will get in that much.

After a couple of preliminary years of annoyance, a LONG time and 400,000 kms ago, I developed a system for Plus 8s. Never fails me.

1. Firstly, I use a expansion method rather than a recovery one. It merely means placing the pressure cap on the reservoir rather than the radiator. Expansion tanks MUST be higher than the radiator and that is why most +8s have the reservoirs on the bulkhead, the highest point in the engine bay. I cap it with a safety pressure cap at 15 psi, as the manufacturer suggests. I do not use any higher because I have no wish to put any more strain on the water pump than recommended. And additional benefit is that you will be able to depressurize the system, faster and safer at the reservoir than the rad. But always be careful.

2. The radiator is capped, not with pressure cap but with a shut-off cap (available at any savvy LR/Rover supplier) These caps are not pressurized and leave the line to the reservoir unobstructed.

3. When filling the rad, I do so to the top with a distilled water solution. (50-50 coolant-to-water to which I add a bottle of Water Wetter (which really does work, just not as enthusiastically as their advertising..figure -2C better).
My goal is to keep my car within the operating range recommended by the manufacturer. My goal is NOT to stop it boiling over when it has to. (only once in 30 years when I joyously blew a head gasket in the Dordogne). Stuff like Waterless Coolants allows the engine to run WAY over the manufacturer recommended limits for engine health. We should WANT the engines to boil over if something is amiss.

4. Once I have the rad filled to the top. I wiggle the car by pushing it to make the rad move a little. Bubbles will stream up to the rad entry. I do that until there is space and I fill again. I repeat the process 3-4 times until there are no bubbles.I close the rad with my non-pressure cap.

5. I then move to the expansion tank. I fill to 1/2-to 2/3ds. Remember, you will be filling the hose from the rad to the expansion tank as well. I over fill to this level to make sure any air I missed will be filled by the excess over the 1/3 of the reservoir which I am shooting for after the system has adjusted. Anything more will be expelled by the system after a drive or two. Any needed will drain the reservoir, so add a little after chaeck after 2-3 days.

Good luck.

Even some later Mogs suffer airlocks, this is a pals 3.7 Roadster with the heater hose routed over the top of the engine, even higher than the expansion tank, since fitted a bleed valve (not shown) which has sorted the annoying airlock forming during winter lack of use

I too use the expansion pressure cap on the recovery tank method, although, there are many who will tell you that is wrong and the pressure cap should always be on the radiator. Air bubbles are prevalent in this era of Morgan cooling and the above method is a good way of dealing with them, it also means all the fluid filling and checking of levels is done at the recovery tank. The system will burp air and fluid out of the recovery tank finding its level, works a treat.

I fitted one to my 4/4 into the heater circuit. Fitted a longer hose so it was above the radiator and heater matrix at the highest point, and put a bleed valve point in. Not sure if it's possible to do something similar on the +8

It’s a shame there isn’t an air bleed valve in the top hose from the radiator. I had a Renault with one and it helped immensely to bleed air from the high part of the system, where it migrates to.
On the Plus8 (2002 model) the method above was basically what I used. My expansion tank was near the rad, not on the bulkhead though. I unbolted it, raised it up and it helped by being higher. Replaced when happy that airlicks were gone/ greatly reduced.Slightly overfilled to allow coolant suck-back as air was removed. Squeezing the top hose also helped get air from it into the expansion tank. Keeping the level in this expansion tank is important to stop air getting sucked back. Any excess will be expelled via the overflow pipe in the filler neck. The cap (15psi) released to let the excess flow out. Later level checks made after a few miles driving. I used 50/50 coolant/distilled water with water wetter.
Mine overheated once when stuck in traffic on a hot day and the fan fuse blew. Replaced the fuse and checked the wiring/thermo switch etc but no problems after that. The fan was always loud when on so an audio back-up to alert temperature getting up! I did some small jobs to reduce this. Making sure as much air as possible went through the rad ( Morgan ali not aftermarket). Morgan airflow leaves scopes for improvement! I believe the rad was slightly under spec as a heat exchanger as it was too near the limit for the thermo switch to kick in. The core should have denser gills per inch to increase hear transfer/airflow surface to marginally increase heat exchange, or even an extra row of tubes that would further increase heat exchange. This would reduce the times the fan kicked in. No overheating but enabling a slightly lower ambient running temp would give bigger leeway to the fan kicking in. Both these are standard upgrades. We used these in the radiator factory as basic upgrades for different engine sizes/ oil cooling/aircon differences for Rover SD1 cars as OE equipment for the assembly factories.

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

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.

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.

Here one can see the difference in simple words.

https://blog.cantonracingproducts.com/blog/setting_up_your_cooling_system_expansion_vs_recovery