Random coolant loss / Can you test a radiator cap

[Pyoor_Kate]

Hiya folks,

So since getting the new engine my car's had random losses of coolant - I can't see anywhere that it's escaping from (as in, there's no obvious loss from any hoses, no streaks running from or pools around the radiator) - but the overflow/whatever it's called hose always has some liquid in it - so I'm wondering if the cap's knackered.

Is there any way to test the cap? Oooh, and does the Ital 1275 need an 8lb cap - 'cos mine's currently got a 4lb cap...*


* I'm thinking about switching back to an 88 degree stat and thought at the same time I'd switch to a 8lbsqin cap, but kinda want to sort the coolant disappearing before I get to fiddling.

Cheers folks.

[rayofleamington]

Ital should have an 8lb cap IIRC.
How low does the coolant go? Does it settle to a low level or does it continue to loose?
Do you have a heater valve on the back of the head (they can leak without it being too obvious)

And lastly - do you know the history of the engine?

[superchargedfool]

hi, caps are easy to test with the right equipment, garage job not diy. But as they are so cheap I would probably say why not put a new one on anyway.

[Pyoor_Kate]

The engine's a just-reconned one; they suggested that it might just be the radiator weeping - but it tends to be fine for days on end and then suddenly drop to below the top of the fins in one go (I always top it up because it almost invariably is below the top of the fins when it drops* dunno how low it'd go if I left it!).

It does have a heater tap - shows no sign of leaking.

I may just throw a new cap on then, and I'll get an 8lb one.

* But seriously, I'll go weeks without it dropping at all, and then it'll disappear twice in one week.

[rayofleamington]

I always top it up because it almost invariably is below the top of the fins when it drops* dunno how low it'd go if I left it!

If it's down to the fins then I'd also be worried! This is somewhere around the level of the water chanels in the head so a bit risky.

Do you have a temperature guage? If so then you've probably already monitored for overheating so not much point for me to ask.

I would be surprised if that amount of water loss is purely from the cap. By the time it gets that low you shouldn't be getting water anywhere near the cap so maybe it's leaking elsewhere

[Pyoor_Kate]

Aye, that's what's been worrying me, but I don't just want to throw radweld in (which is what the engine place suggested) - without knowing where it's coming from. If it *is* leaking from the rad then I'll just get a new rad, quite frankly, rather than put radweld into my new engine.

Yeah, temp gauge is fitted - it's not overheating so far as I can tell...

[rayofleamington]

I'd agree with you on the radweld - it's better as a last resort in an emergency, not a long term fix for an undetermined problem.

[mike.perry]

I get the same sort of problems with my engines. The traveller sometimes empties the coolant into the sump so I get a grey emulsion on the dipstick, I think I may have a crack in the block between the water jacket and the sump as there is no oil in the water.
The Series MM just likes losing water occasionally, no signs of dripping, trouble is when it does leak the water evaporates off the hot engine before I can spot the leaks. Like your's its very hit and miss so I just stop and check it every hour or so.
Was your engine rebuilt by somebody else as it is worth checking that the head has been torqued down properly, or you could be getting water leaking past the head gasket. It may be worth giving the engine a compression check to make sure that the head gasket is ok.
I'm not a great fan of radweld as it blocks all the water passages, and the bottom of the radiator and engine water jacket get filled with sludge.

[Mogwai]

Have you had the cooling system pressure tested? if its using that much coolant it must be going somewhere if its not leaking externaly could be the headgasket
may be worth taking the spark plugs out to see if any of them look washed which would indicate this

[Pyoor_Kate]

Well, the 500 mile check's been somewhat delayed (I discussed this with them) 'cos of a leaking oil-breather - which they want to replace, but I need to have 3 hours free the day I go up to see them...

...so the head wasn't retorqued at 500 miles - but the oil that came out when I changed it was clean and water/sludge free.

[Leo]

Check all your rubber hoses including the bypass
They can be water tight when hot but lose water when cold through the hose clip joint
Best to tighten hose clips when system is hot
Check that bypass hose again, they can be very difficult to seal

Leo 69 Traveller

[rayofleamington]

very good point! I was only thinking of places likely to loose water when hot, but at this time of year it's also possible to get leaks because of the cold. Most of thje time a hose will tighten when it's cold as the diameter will shrink - but on a small hose like the bypass hose it can be sealing on a wing and a prayer at the best of times.

[alzax3]

I've got a pressure tester, but I see you're a bit far from Cornwall to borrow it! The old Marina engine in our van used a fair bit of water, without any obvious signs of leakage - when I put the tester on it and pressurised the system I had three 'micro mist' jets spraying out (much finer than a hair) two from the rad core and one from the bottom hose. Like I said, neither showed up in normal running. (The same tester does the caps too - it showed ours was weak, but of course putting a better one on would have increased the water loss!)

[bmcecosse]

Simply put a catch tank (plastic bottle is fine) on the end of the overflow pipe from the rad. You will then see if any water has been blown out - and when the engine cools - it will suck it back in anyway! I would stick with 4lb cap - the only reason for higher pressure is to delay boiling - and it should really never be near boiling point anyway. The 88 or even 92 stat is a very good idea in winter - go for that. And be sure to keep some anti-freeze in there !
The 'leaking' oil breather sounds ominous - is it blowing excessive oil/fume from the breather ?

[rayofleamington]

and when the engine cools - it will suck it back in anyway!

unless it's a Minor.

[Judge]

Unless it's a Minor like mine Ray, with an expansion bottle

[bmcecosse]

If it doesn't suck in the fluid - there is something wrong with the cap. My Minor certainly does! The Minor cooling system is no different to any other system of that era.

[mike.perry]

Surely with an expansion bottle the pressure cap is on the bottle not on the radiator. The coolant won't draw back into the radiator if it has a pressure cap. Or have I missed something?

[bmcecosse]

It does on mine ! Maybe different caps have different venting arrangement - but I have had more than one cap on mine -and all do it. When I take the cap off - the rad is always brim full - and some water in the catch bottle. Yes - a proper 'expansion tank' as fitted to the 1100/1300 BMC range - has the pressure cap on the expansion tank - as does my TR7!

[Pyoor_Kate]

The 'leaking' oil breather sounds ominous

Nah, it's a pin-prick hole in the breather which made itself apparent the first day I drove home!