Series 3 coolant level ... what's "normal"

Hi all,
looking for some advice. Just had a new Turner Gasflowed Performance head fitted and new 82 deg thermostat
put in. Trouble is now i'm losing coolant, i think?
Before the new head (replaced as a result of the head gasket blowing between cylinders, I bit the bullet on a lead free head), my coolant level was right to the radiator neck, like right to the top. Temperature gauge was reading below middle as a result, i guess, of no thermostat fitted.
So now all back together (engine build done by local classic car garage, top guys, plenty of experience),
the coolant level keeps dropping to the height of exposing the radiator fins/matrix/core.
Thing is I have no idea what the normal level is? Should coolant be covering the core?
I top it up, but after 80 miles or so, it's back to that level. I haven't left it to go lower, if indeed it does as i'm not wanting to overheat the new head!
Also noticed the temp dial is reading 3/4 up the dial now. Have look online and a 82 deg thermostat does seem to give this reading. The dial sits there quit happy even in a hour traffic jam i got stuck in the other day.
I've had the garage compression test the head, 140 psi on the cylinders, no smoke, no water when warm from exhaust.
I can see no visible leaks from water pump, hoses etc. Just fitted a new 9lb cap as well.
No oil contamination in water, no water in oil (Although oil filler cap does generate a thin layer mayo on the underside even after i clean it, the guys told me that a head that long does generate moisture, does yours?)
So either something has happened as a result of the rebuild or i'm topping it up to much and it's spitting it out to the overflow under pressure.(which was quite low and never seemed to get any higher).
Any help greatly appreciated,
Regards,
Mark

Level *should* sit above the core in the radiator, if it's only 1/4" down from the top of the core i wouldn't worry if its not doing anything else untoward, ideally should sit very roughly 2" down from neck

Think the only thing you can do is top it up, fire it up and watch. If its not coming out the engine it looks like its going in it.

thanks Grem, at the point that i chicken out and top up, it's sitting level with the core, ie i can touch it. I'm wondering if i should leave it and see if it drops and further?

Showing no obvious signs of going in though? Tick over smooth, paper on the exhaust tip, no suction, no smoke, no water either.

anything you can suggest Bobsticle

Some leaks are hard to find as they only appear when at temperature under pressure which is why I have a device that fits into the headder tank to pressurise the system.
Do you have a pipe on the expansion overflow to catch any dribbles?

Did you get the coolant checked

yes have a expansion bottle, pipe goes from top of rad to expansion bottle.. Coolant checked, no .... have a gunson on order ...... would the % make a big difference to the level? I did notice that there was no antifreeze on the invoice, but the coolant is green, so might not have charged me, but ordered a Gunson meter to check anyway.

I changed my radiator recently and had exactly the same problem. Exactly. After much head scratching I found a small leak coming from the connection between the cylinder block up to the thermostat. It was cured by nipping up the juub clips. I found the leak when it was cool. Bastard leak was making it overheat in traffic. Sticks to the N and takes usual 3/4 miles to get to that temp.

Has your radiator cap got a seal fitted ie neoprene or rubber where it meets the radiator , iof not the hot water goes into the expansion bottle biut cannot be suckeded back as the engine cools because it sucks air instead.
I know because I bought a new cap with no seal and it took me two years to find the problem , made a seal out of damp course membrane and no bother since.

John, I'm really hoping it is a simple leak, but can't see water leaking from anywhere.
I'll check all the pipe clips at the weekend. Had top, bottom and bypass hoses changed.
(Bearmach)
Did you see anything on the floor as a giveaway?
Hi Blackburn, yes, it's a Land Rover genuine part, has a rubber seal.

I kept looking for water dripping. Eventually I found it was running down to the bottom hose and then dripping onto the diff and then running back along the prop shaft. I too suspected the new cap but mine is ok.

What does the gun sons device check?

As its running hotter the pressure will be higher so more likely to leak.

Get yourself a pump to pressurise the system, look on eBay there are loads.

You may not see the leak if the engine is hot.

Many years ago I used blotting paper to find a steam leak.
The paper changes colour quite a bit when wet so I just pointed it at all the joints until one of them left a dark patch.
I bet you can't even get it these days.

If you run it at idle and have a look over and under once up to temp you should be able to find it. Don't worry about overheating you'll smell it before it does any damage.

Might not have made my point very well this is a pic of my rad cap that did not allow the water to be sucked back from the expansion bottle.
Has a nice rubber seal at the inner rad lip but when the water expands and goes into the expansion bottle the thin silver metal seal that seals to top of rad outer lets air back in so water does not return from expansion bottle.
Parts book show a seal 564999 as seperate part to radiator cap.

That's not right looking and I've never come across a separate part number for the rubber seal. Normally sold complete for about 3.50 ish. Hope you find the leak it's annoying.

Looks like you've found the bother.

Hi all, haven't had any time over the weekend to look at the problem and try and find the leak.
Half filled the expansion bottle up (as it was nearly empty) and topped up the rad. Going to see this week what happens.
Oil filler cap still has a thin layer of white mayo on it even after I cleaned it.
Can I ask you guys, what does the inside of your cap look like?
Blackburn, my new cap has 2 black seals, larger one on the top and the other as per your photo.

Mine has the two rubber seals. If you've only the one that may be the problem.