Coolant Loss

[myoldjalopy]

Yes, if you compare them, the SII radiator (also used on early models of the 1000, I believe) is taller than later versions, with more space above the core, so I suspect the SII core can be covered with a greater depth of water before it vents out the overflow.

[geoberni]

When I brought my SII, he had a standard S3/5 low top radiator fitted; a couple of years ago I obtained an original high top SII radiator and the Rad Cap from the old one, which is pretty old, transferred over without issue.

See images.
Measurement of 28mm is from the inside of the cap top to the rubber face.

I keep my water level about 1/2" above the core when looking into it.

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[myoldjalopy]

Well, getting back to the OP's original problem, let us hope a new radiator cap will solve it. Despite his saying that he has flushed the system, the fact that he alludes to 'rusty' water coming out the overflow suggests another flush might be sensible.

[jaekl]

Honesty, 4% expansion from room temperature to boiling is higher than I thought it would be. Using that figure and a 5 1/2 liter cooling system would be 220ml or about 7.5 oz. expansion. The upper tank is at least one liter. That's just water. What does anti-freeze do to the expansion rate?

[1000wannabe]

A number of interesting comments, thanks to all.
I still believe the main issue is the cap.
The measurement shown in the post earlier by one of you at 28mm is not what mine is (calliper measurement shown).

The reference to reflushing is potentially valid even though the cooling system has been drained several times and the heater is clean (flushed). I believe the recent stir up of 'rusty' water is because the recent trips are the first time the car has been used properly in a decade AND I discovered that the car had been fitted with the wrong water pump and was effectively doing little to nothing as far as water circulation. My new pump spinning at whatever 80 kmh is in engine speed has obviously disturbed sediment..

[philthehill]

What was different about the water pump fitted that gave you the impression that it was wrong?
The only differences in the water pump is the style of the impellor and the depth of the impellor. They all work.

As regards the cap - If you fit the cap and you have to press the cap down against the cap spring to fit it then the cap seal is making contact with the radiator filler neck seat. Other than altering the pressure of the cap that is all you can ask for.

[Bill_qaz]

Honesty, 4% expansion from room temperature to boiling is higher than I thought it would be. Using that figure and a 5 1/2 liter cooling system would be 220ml or about 7.5 oz. expansion. The upper tank is at least one liter. That's just water. What does anti-freeze do to the expansion rate?

Solutions of propylene or ethylene glycol have higher coefficients of expansion compared to water. The higher the concentration of antifreeze the greater the expansion volume required
The header tank would be hottest part of the radiator, so possibly expansion is higher than the total cooling system volume. Also if the cap is not sealing, the non pressurised water has lower boling point.
As said in posts ,different radiators series 2 to 5, and that's the level mine always runs at quite happily. If yours needs to be filled higher then so be it. I was just replying to the OP that filling too high, will always vent the excess, due to expansion via overflow, exacerbated if cap is not sealing.

[1000wannabe]

Thought I'd report back...
Firstly, Phil...
The heater only had a slight warmth to it, even at normal temp and only at higher engine speed. Having read through the forum, I started with a back wash. Almost no debris, good flow...
So then i set it up with nothing on the head tap (open) filled the radiator and as water rose, got good flow out of the tap.
So then I bled the heater got good flow...
So then checked thermostat. Previous owner had to replace the housing due to corrosion, so I pulled it to make sure there was a thermostat. There was. Relatively new looking 82 degree. I'd read about corroded impellers. The pump was a cast iron unit, so I removed it and found it was a 950 short impeller. If you know 1098 engines, the casting is thicker.
The car came with a spare rebuilt 950 but no pump fitted. When I measured the protusion of the impeller, compared to the casting, the 950 pump wasn't even clearing the thickness of the front block casting. Correct pump and instantly the heater works!

As for water loss...
I made a square section 'O' ring to sit on the seat and take up the difference between the measurement of the neck depth and my actual cap.
A comment before mentioned about feeling the resistance when the cap is closed being the seal seating.. this isn't entirely correct. Part of that resistance is the thin metal disc that seats on top of the filler neck.
My issue seems to be the variance of depth of the neck seat as well as also having some variance in the cap.
With the extra seal, water level as shown and cap on, I did a 10 min or so drive at 80kph. Engine warm, heater nice.
When I got back, although the cap wasn't hot to touch, there was finally a small amount of pressure that you'd expect slowly undoing the cap, same water level and no expelled water out the overflow..
I have a new 28mm cap coming..
With the water issue seemingly sorted for now, I have now developed a slightly psychotic charge rate from the dynamo which I assume is unhappy about being woken from a 10 year rest... (I have a brand new electronic regulator and wiring loom...)

Cheers
Chris

[1000wannabe]

Hi Guys,

I thought I'd share for those of you who were good enough to contribute to this thread...

My very first suspicion was confirmed today.
I do in fact have a leaking head gasket...

I took the car to get it registered again after many years being off the road, so at least there is one more Morris back on the road, but, even though the water level stayed where it was, the coolant was a bit more scummy and the 'mayo' in the rocker breather made me wonder. A series engines are known for doing this unless they get really warm, but I was also suspicious of the fuel consumption...
Advice from a mate who has recently retired as an A grade mechanic and first class machinist of 50 years said to rule the head gasket out, put it to bed then focus on other areas.
So I did his recommended cylinder pressurising test.
I was suspicious when i got to number 3 cylinder. I couldn't be certain if I had seen the water level change..
When I got to number 4, I thought it had a little. I went to check the air leaking out the exhaust (I blocked the tail pipe with hand to confirm) I returned to see the water level rise and flow out the overflow (I had the cap off).

So now I know... a head gasket at the minimum is needed...

[oliver90owner]

The simple way to make a check for a leaking head gasket is to completely fill the radiator to the filler neck and start the engine. A head gasket leaking into the cooling system soon becomes obvious as bubbles from the radiator. The other usual check is, of course, a compression test, particularly for a failing gasket between numbers 2 and 3 cylinders.

Expansion of water is, btw, nowhere near 4%. More like 1.7%.

Do check the straightness of both the head and block before installing a new gasket. It is more likely that the head will need skimming - or a further gasket failure is likely to ensue.

[1000wannabe]

Hi Oliver,

I was aware of the test you mention. Very early on in this thread, I already mentioned that the car did not have any of the classic failed gasket symptoms and that included any bubbles in the coolant or oil contamination.
The coolant remaining at the low-level many people find as normal with the added issue of the cap meant that eventually when under driving loads, the excess pressure in the system was just venting out the overflow.

A compression test is not always a good indicator of head gasket failure, especially when only slight like mine.
The actual test used is to fit an air line/pipe into the spark plug bore and pressurise the cylinder. Although not the same pressure as during combustion, it does provide sustained pressure for as long as you leave it connected. That results in a rising coolant level without any temperature factors. In my tests, I didn't once have any air bubbles make it to the radiator neck to escape, the level however rose very subtly testing #3 and then rose up to overflow at a steady rate whilst the cylinder was being pressurised.

The components including head will obviously get checked when apart as the engine is new to me so I don't really know it's condition...
Cheers
Chris