Keeping the rad full

[RobThomas]

It seems silly that the rad, if filled when cold, will expand during the first drive and dump a load of water overboard. On my 1952 I added a plastic bottle to the overflow system so that when the rad threw out some water it was caught and then sucked back into the rad as the engine cooled. On the 1966 car I went up-market and tie-wrapped an empty bottle of 'Jacobs Creek' to do the same task. Today I decided to make a slightly more fancy one for the Lowlight. I cut up an old Tri*mph master cylinder for the cap, turned a small ali thingy for the outflow and cut up an old piece of ali tube that I found in the garage and welded end caps onto it.

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Not sure if this is even necessary but it can't hurt. Does anyone else have a shortage of water in their rad after a long/hot run?

[SteveClem]

I just let mine dump water when they get hot. It's not much really.

[RobThomas]

I can normally get about 1 litre into the MM after a few days of normal use.

[philthehill]

I have a Marina expansion tank fitted to my Minor and would not be without it.
When I first fitted the expansion tank I just fitted a non pressure cap to the Minor radiator and the overflow pipe connected to the expansion tank with the correct pressure cap fitted on the expansion tank - it worked very well for both road and track.

[RobThomas]

Assuming I haven't got the concept ar53 about face, if I keep the standard 4psi MM rad cap in place it should dump overboard into the 'pot' which is vented to air and then suck it back up via the deep pipe inside the pot that connects to the old MM rad overflow pipe. The MM rad cap does have a -ve pressure release valve, doesn't it?
In you set-up, Phil, does the Marina 'pot' lid act as the main pressure cap and thus is really a pressurised expansion of the rad capacity? I'm not missing a trick by doing it my way, am I?

The Midget had a 15 psi cap on it and coped alright. Is there a good reason to restrict the pressure on an MM? The rad and all the hoses are new.

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[philthehill]

Rob
In the top photo the expansion tank cap has the main pressure cap.
The radiator is filled to cover the radiator core - a small amount of coolant is placed in the expansion tank.
When the Minor coolant expands it is pushed into the expansion tank and when the engine cools the coolant is sucked back into the main radiator.
That's the theory and it worked.
The feed into the Marina expansion tank is at the bottom. The expansion tank also has a overflow outlet which as the coolant cools will allow air into the expansion tank to replace the coolant which has been sucked back into the radiator.
In the bottom photo the Marina expansion tank is more of a remote header tank with main pressure cap - if the expansion tank is not overly filled it will accept the expansion of coolant via a service pipe and as the engine cools the coolant returns to the main radiator in a similar process to that above.

The process as you describe above is correct and the parts you have made will work.

As no doubt you are well aware - raising the pressure in the cooling system increases the point at which the water starts to boil.
As regards raising the pressure on a Minor cooling system - in reality the Minor is overcooled so should not need a higher pressure radiator cap.
Raising the pressure increases the risk of coolant loss through leakage as it finds the weakest point in the coolant system i.e. old radiator core/water pump/hoses and the engine may find itself without coolant for the wrong reasons.
Phil

[BLOWNMM]

On my MM I have a coolant recovery system fitted. The overflow tank is fed from what is normally the overflow pipe. When the motror heats up the coolant expands and the excess flows into the overflow tank. When the motor cools down the fluid in the O/F tank is drawn into the radiator via the special recovery cap. This recovery cap has a double seal to enable it to work. A standard single seal cap as fitted to a Minor will not allow this recovery process to occur. It will only allow the release of coolant but only return air to the system on cooling, not coolant. If a double seal recovery cap is to be used it cannot be used with a normal Minor tall neck filler as they are not manufactured for the tall neck filler. I had my radiator cleaned and fitted with a short neck filler by a radiator specialist to allow a recovery cap to be used. It is not uncommon for me to have to top up the O/F tank to the lower or cool mark at 6 month or more intervals and then only 50 or maybe 70 ml of water. I also use a 7 lb. cap which the MM radiator and my cooling system handles with ease
http://www.tridon.com.au/products/Trido ... iator-caps

[philthehill]

Bob
If the pipe from the radiator to the overflow tank enters the overflow tank at the bottom (as per my top picture) - only coolant displaced from the radiator will be pulled back into the radiator as the air entering the overflow tank will be above the coolant and cannot be drawn into the radiator until all coolant has been expunged from the coolant overflow tank.
Atmospheric pressure will push coolant from the overflow tank back to the radiator as nature abhors a vacuum.
That is why I like to prime the overflow tank with coolant.
It should be noted that the overflow tank needs to be set at the right height in relation to the radiator overflow pipe to get the best out of the system.
The coolant tank filler in the second picture is placed slightly higher than the screwed filler cap fitted to the Marina thermostat cover.
As I said above they both work for me and I never had any cooling problems with the set up.
Phil

[RobThomas]

So, Bob, does the second seal work to seal the metal winged lid (for want of a better description) against the top face of the rad filler neck, thus sealing the filler neck from any air? From what I can see, the standard cap has a -ve pressure release built in to the bottom of it and, if the top seal were effective, would only allow the contents of the overflow system to be sucked back in.

I have the 'large' MM filler neck.

[philthehill]

Rob
You have described the system in my first photo exactly.
The cap on the actual Minor radiator just seals the radiator filler cap and does nothin else.
Any expansion of coolant is therefore allowed to flow to the expansion tank without hindrance.
Phil

[BLOWNMM]

When I fitted my recovery system I took notice of all the web sites which stated that recovery cannot occur unless a proper recovery cap is used. I did not question it. My O/F tank is mounted at a height about halfway up the core. The normal O/F pipe is connected to the O/F tank at the bottom. I believe the slight loss over 6 months or more is due to the fact that the hot coolant entering the tank results in the air volume containing a high amount of moisture and is expelled through the O/F tank vent hole. When the motor cools down the air drawn into the O/F tank has a relatively low amount of moisture. Our relative humidity levels are about 10 - 15%. This means every time the motor warms up and
this cycle repeats itself, a little moisture is lost in the expelled air from the O/F tank. I have included a couple more links which claim to explain how a recovery cap operates. As a matter of interest I always use demineralised water which is free of chlorine and fluoride both of which can cause bad corrosion problems.
Bob
http://www.mgb-stuff.org.uk/radcap.htm
http://www.tridon.com.au/databank/docum ... r-Caps.pdf

[RobThomas]

Thanks guys. I continue to learn, which is a good thing.

The early MM cap I have has the steel top seal without rubber and I was going to cut a thin rubber seal to go in there so it looks like I was on the right path. The early cap has a much more fancy system for the pressure release (I'll get a photo tonight) but I tried the suck/blow method and it releases both ways (did you know that the average human can 'puff up to about 2psi through lung action?)

De-mineralised water...great idea, Bob. We have one of those condensing laundry driers so there is a good supply.

[philthehill]

Bob
Many thanks for the links.

The cap on the Minor radiator in my first picture is of the non pressure TRC Series (sealing cap) as listed in the 2nd link.
The only difference between my set up and the cap/location in the first link is that the normal Minor non double seal pressure cap has been relocated to the overflow/expansion tank.
The same process of coolant expansion and contraction occurs whether the pressure cap (double seal cap) is fitted to the radiator or to the overflow/expansion tank (normal cap).
As you have indicated - the pipe to the overflow/expansion tank must be below the coolant level in the tank when the engine is cold and there must be enough room in the overflow/expansion tank to allow for the hot and expanded coolant to flow into it without spilling out of the overflow/expansion tank vent pipe for the system to work.
The set up (first picture) is a near replication of the Marina cooling system from which the coolant overflow/expansion tank came from but utilising the existing Minor radiator.
For info - the radiator used in the second picture is a light weight alloy/plastic one sourced from a Vauxhall Astra which has an auto activated cooling fan and manual override.
Phil

[BLOWNMM]

Rob
Have you considered fitting a sacrificial anode to protect your Alta head. Easily done and although magnesium is the lowest, Zinc would do the job admirably. Zinc is 3 on the Galvanic table as against aluminium starting at 6. See link.
Bob
http://www.eaa1000.av.org/technicl/corr ... lvanic.htm

[Declan_Burns]

I have an expansion tank on my MG TD which is a non-pressurized system. It has no cap-just a simple vent to the atmosphere. The bottle (500ml) is in the battery box which means it is roughly at the same height as the top of the rad. The tube entering the bottle goes right to the bottom of the bottle and incoming coolant simply forces the air out the vent at the top. The opposite effect on cooling and the coolant is drawn back into the rad. It works perfectly and is a common mod on T-series cars. The silicon hose is just to isolate the bottle from engine vibration.

Regards
Declan