Morris Minor Owners Club

Hi Guys,
I'm looking for some input on my coolant loss issue and or radiator cap concerns.

My (new to me) late 56 Series 2 has been undergoing work getting it ready for registration.
The previous owner over time made 'improvements' and it it now fitted with an APJMH prefix 1098 engine onto a smooth case box that on the side says it was fitted with 1000 ratios in 2010. I'm suspicious, but think it still has the series 2 diff ratio.. anyway..

My first cooling system concern was because i had no heat in the heater unless I had high engine revs.
I flushed everything and got good flow and clean water quite quickly. So I went to the thermostat. The one fitted looked new but got replaced anyway with the same 82 degree.
I bit the bullet and pulled the pump to find it had a 950 short impeller pump that didnt even enter the water jacket. Success I thought!
New pump, everything back together, I have heat.. yay.. but..

I headed off for the road worthy test (our version of an MOT). Its a 30km trip each way, cruising at 75 kph (because I thought the engine sounded very busy). When I got home, I noticed the rusty water in my clean engine bay from the overflow and it had dropped the coolant level down to not far above the core.
Fast forward 2 weeks and I went back for the final test. I checked when I arrived and lo and behold the water was down again, so I filled it back to an inch below the filler and drove home.
Same again!
I've checked and it seems I have the tall tank Series 2 radiator as you might expect (it has been refurbished).
So I checked the cap and its a g.280. Apparently the cap for a long neck filler.
I put some paint marker pen on the rubber seal and fitted the cap to find only a slight transfer to the filler neck sealing lip in one spot as you can see. So i've measured and found the following:
From the sealing top surface of the filler neck to the same on the lip at the bottom of the neck is between 26.8 and 27.43mm varying from side to side. So I thought OK, a 28mm cap is the right one, so I checked the cap, a made in the UK G.280 which is apparently the correct cap and from the sealing surface of the metal 'disc' to the sealing face of the rubber seal its 25.94mm. I can only assume its not seating.

The car runs beautifully other than a little bit of pinking up one steep hill (unless you change down to 3rd) but I haven't checked the timing yet, it has no signs of overheating at all (radiant heat wise or running behaviour) no typical signs of head gasket issues (oil contamination or water contamination) and there have never been any bubbles in the coolant other than the settling of it after I had drained the system to replace the pump. The heater is nice and warm, but not crazy hot and the cap was not too hot to touch or under pressure to open when I got home. its also winter here, about 12 degrees C.
I can't tell if its pressurising the system and forcing the water out (had this before in an Austin Tasman whose pipes got really firm then lost coolant) as I've not been able to drive it anywhere until its registered other than what I've had happen so far.
You can see in the photo how far down the coolant is now.

Anyone have any thoughts?
Cheers
Chris

From your measurements the cap is short in the neck by 26.8-25.94 = 0.86mm and 27.43-25.94 = 1.49mm. So possibly not seating. Put an additional sealing ring in the top of the neck and see if it seals. It may be seating as is but not sufficiently when hot.

Thanks for your thoughts. I did consider that, but don't have anything suitable to hand to try at the moment. I was looking to get a new cap but I'm not sure where the 28mm is measured from. If it was from the same points I measured it would solve the problem..

The correct coolant level is just covering the core not to bottom of neck, you are venting the excess via the overflow when it warms up and expands.
To prove your cap not sealing put a thin bead of silicone around the seating area of the neck and allow to dry before retesting. Or an O ring if you can find one, sink plug?

A small detail but I haven't read anything regarding the pressure of your cap? It should only be 4lbs.
It is unusual for a Minor to overheat and loose coolant. As Bill says, you don't need to overfill.

Thanks for your replies.
Yes it's a 4lb cap.
Bill, are you saying that the level as you can see it in the photo is correct then? I'm sure I read somewhere that it should have been higher, but it's many years since I've had a Minor 1000 and my last car was a 51 side valve high light, so different again..

It sounds from your description that the water level is normal. I can see the water level just above the core in mine.

I would just use it and resist the urge to top it up again and let it find it's level. If it drops below the core you have a leak somewhere

Thanks mowogg. I have had many different cars over the years and I've never had one with a water level this low, including related BMC cars. I have a mate here with a 950 series 2 and his also sits lower (perhaps a sniff higher than mine at present) and he said his spits out excess every time.
Having said that, the measurements dont lie and the cap can't be sealing so I'll look into a cap and or supplementary sealing for now and see where the water levels out.
There are no leaks other than what comes out the overflow.
It does make me wonder what was the point of such a big header tank on what appears to be an over cooled engine, especially when you compare to say a Mini set up..
It's reassuring to know that the water level isn't considered to be alarmingly low... I'll sleep easier now...

1000wannabe wrote: ↑Sat Jul 13, 2024 11:55 am Thanks for your replies.
Yes it's a 4lb cap.
Bill, are you saying that the level as you can see it in the photo is correct then? I'm sure I read somewhere that it should have been higher, but it's many years since I've had a Minor 1000 and my last car was a 51 side valve high light, so different again..

Yes that's where mine runs so the core is covered maybe 1/4 to 1/2 max anymore just vents out of overflow, it tends to find its own level if I've topped it too much. I have a temp guage fitted and it does not overheat.
Agreed you do need the correct cap as far as I know only two length available.
https://www.morrisminorspares.com/cooli ... ly-p829632
It lists the models for the 28mm cap
Is yours ohv engine and is the radiator correct for model?

Hi Bill,
Yes it's OHV. As I mentioned, a 1098. The radiator is correct for the series 2 car, but series 2 never had a 1098.
The cap I have is correct for the radiator but the measurements just don't add up..

Has it got a large diameter seal in the top of the cap? Can't see from your picture, if so try removing it and take the measurement, The pressure seal is the smaller onto the neck base it doesn't need a top one.
Worth a try to run with top seal removed if it has one

Hi Bill, no. The upper cap has a very thin metal disc that seals against the very top surface if the filler neck.
The issue is the lower rubber seal that doesn't meet the neck lip. This has to be correct otherwise the radiator is effectively open to the overflow which mine is. So it doesn't build the normal radiator pressure and water can just rise and flow out.

A new, correct radiator cap is so cheap that it would make sense just to purchase one wouldn't it?

I agree. My cap is marked as the correct one already.
Unfortunately they are only available from specialist suppliers here, I've tried all the mainstream parts supplies already. I need to get one in the next few days as I have to take the car to the department of roads, registration etc to get its registration completed.
A new cap was always on the cards, I just wanted to try and find out more as it's likely I'll end up with the same dimension cap, hopefully its just manufacturing tolerances and I'll be right..

1000wannabe wrote: ↑Sat Jul 13, 2024 11:07 pm Hi Bill, no. The upper cap has a very thin metal disc that seals against the very top surface if the filler neck.
The issue is the lower rubber seal that doesn't meet the neck lip. This has to be correct otherwise the radiator is effectively open to the overflow which mine is. So it doesn't build the normal radiator pressure and water can just rise and flow out.

So as you say most likely,the cap out of tolerance as I suggested put a silicone bead in neck or an o ring or rubber washer to make up distance until new cap is sorced.
Good luck.

What is in the coolant that is expanding the volume of the upper tank? There is either trapped air or there is localized boiling. Ensuring that the cap is sealed only allows the pressure of whatever vapour present to rise to the cap rating. It's time for a good flushing.

jaekl wrote: ↑Sun Jul 14, 2024 12:58 pm What is in the coolant that is expanding the volume of the upper tank? There is either trapped air or there is localized boiling. Ensuring that the cap is sealed only allows the pressure of whatever vapour present to rise to the cap rating. It's time for a good flushing.

If you read the OP it's just excess water from overfilling combined with cap that doesn't seal so overflow is permanently open

Water does not expand enough to to displace almost the volume of the upper tank. The additives in the coolant may expand, but that much? Most of us all have the same engine. How many need to run with the coolant just over the tubes? Something isn't right here.

It looks low to me too. In my SII (with the tall radiator) the coolant level sits permanently at 1 and 3/4 inches above the core..........

jaekl wrote: ↑Sun Jul 14, 2024 2:32 pm Water does not expand enough to to displace almost the volume of the upper tank. The additives in the coolant may expand, but that much? Most of us all have the same engine. How many need to run with the coolant just over the tubes? Something isn't right here.

Water expands Approx 4% from 20 to 100 degrees centigrade .
1/2 inch above tubes does not mean almost the volume of the tank is lost at all.

Perhaps series 2 radiator is different, my series 5 with same 1098 runs about 1/2 inch above tubes, any more just vents out of overflow.It was fitted with a replacement double core radiator according to the records.Has recently fitted new stat, cap and waterpump.
No overheating, no pressurising, and no further loss when at that level