43 replies to this topic

[jime17]

Hi all,

My 91 998 carb auto's coolant keeps disappearing.

Its a gradual process, disappearing from the top of the wire loops to below the perforated plate in the rad over the course of 4 or 5 9 mile journeys to work and back.

It doesn't seem to leak. I check after each journey with the engine running, then with it off and then when cool. No puddles.

My guesses are its either blowing it out of the overflow pipe during the journey a bit at a time or its using it.

The thermostat appears to work as I ran it with the cap off topped up and I saw the change when the water started to circulate in the top of the rad.

There's no evidence of froth in the oil and likewise none of oil in the water. Also the exhaust doesn't seem to drip water.

There is a new 15lb rad cap on so I assume that's ok.

The heater matrix gets hot and I can't see or feel any sign of leaks.

the hot air does seem to have an odour, but unsure if that's just the smell of the carpet and soundproofing getting blasted with hot air and which is a touch damp from rain water finding its way in somewhere.

Has anyone got any thoughts?

[Stu1961]

Not an expert on cooling systems but sounds like head gasket is on it's way out to me.

[jime17]

Was wondering that, but no signs of froth in the oil.

Car is running best it ever has. Doesn't seem like any loss of compression. Will have to test that to confirm I guess.

[Cooperman]

If there is a slight leak into the combustion chamber then there won't be any emulsification in the oil - it will simply let water into the combustion chambers when the engine is cooling down.

You may have to simply remove the head and fit a new head gasket. A 2 hour job.

[carbon]

If the radiator is original then it's possible that this may have a slight leak from the radiator matrix, had this on my clubby estate many years back.

 

There was no sign of a visible leak, probably because it only happened when engine hot and system pressurised. Being a slight leak it probably just evaporated off helped on its way by the draft from the radiator fan. When I fiannly took it off there were quite a few of the gills corroded through.

 

Radweld can work wonders for slight leaks...

[Stu1961]

If the cooling system is leaking coolant into the cylinder bore/s I would suspect 99.9% of it will be expelled into the exhaust system

so you won't see any signs of it getting into the engine oil, I'm not saying that can't happen as a sudden major failure of the head gasket

it will probably.  

 

Sounds as if you had a relatively small leak which is getting to the point now where it is creating an issue. You also will probably not see

any signs of the lost coolant at the end of the exhaust pipe because of the heat of the exhaust gases though don't quote me on that one

 

Is the coolant clean or dirty, if dirty this can also indicate that combustion gases are getting into the cooling system (Going the opposite way) 

 

Stuart

[jime17]

Thanks all. Really helpful.

Cooperman, what's the best approach to taking the head off? Can it be done with the manifold connected? It blows where it connects to the Down pipe and so i need to reseal it, so if I can get away without disrupting all the gaskets between manifold and head and manifold and carb, id rather.

The water is just rusty by the way so that's why its easy to see its not leaking. When the old rad cap was leaking I used to leave bright orange trails where I pulled up anywhere!

[Cooperman]

You can remove the head with the manifolds connected and just disconnect at the manifold to exhaust down pipe and leave manifolds and carb on the head.

 

If there is a small leak into a cylinder bore do the repair sooner rather than later as an ingress of coolant will erode the head and/or block and is it erodes the block the engine will need to be completely stripped to skim the block deck. I had to fix a very early 998 Traveller where this had been allowed to happen. It was losing a small amount of water over a few months and the block deck had to be skimmed to ensure a seal when a new gasket was fitted. A very expensive fix for what was initially a very minor problem.

[jime17]

Ok thanks.

Is there a way to definitively diagnose a slight gasket leak or is it simply take the head off?

I guess I should be hoping the block isn't cracked?

[Stu1961]

Might as well take the head off and at the same time flush out the cooling system
as it sounds like it is long overdue going by your description of it.

[Cooperman]

A cracked block on an A-Series would be very unusual. I've never seen on in over 50 years of messing about with them. I've seen cracked heads, mainly on early Cooper 'S's and heads with max. oversize valves.

In your case I would suspect a slight gasket weep into one of the cylinders.

Just whip the head off, clean up the block & head face and fit a new gasket to be on the safe side. It's just an evening's job, assuming you have the right tools, and then you know it'll be OK.

[jime17]

Sorry another question.
is it necessary to remove the rocker shaft and rockers or can they stay on the head.

Haynes seems to suggest you have to remove them, but again id rather not.

[Cooperman]

The back row of cylinder head nuts also hold one set of rocker shaft fixings, so, yes, the rocker shaft must be removed and the valve clearances re-set correctly after re-fitting.

 

Head removal sequence is:

 

Remove rocker cover,

Drain coolant

Remove radiator top bracket

Remove top hose

Remove heater hose

Undo the carburettor connections - fuel, choke and throttle cable

Undo exhaust manifold to exhaust down pipe clamp

Remove plug leads & plugs

Undo the b1/2" AF rocker shaft nuts

Undo all the hear stud nuts

Remove rocker shaft

Remove all 8 push rods

Lift entire head and manifolds and carb from engine block.

[jime17]

Sorry one last question I promise.

If I remove the pushrods, when I put them back, will the rod ends just drop back into the cam follower or do I need to take the tappet chest cover off?

[sonikk4]

It may pay you to drop the heater matrix out before you do the head. I had steam and a funny smell coming from the heater vents but no sign of leakage. Dropped the heater and found water in the case but not enough to drop out.

I never checked the fluid levels as the car as it was parked up. Anyway the matrix was rotten.