Thread: Radiator Overflow and no power after highway

Cut the overflow hose into the bottle with an angle cut, stop it sucking to the bottom of the bottle.

Check that the rad pressure cap has a small easy-to-lift button in the centre, this allows the coolant to be sucked back in. I have seen these gunk up and jam shut.

Filling the radiator to the top will always cause some coolant to escape with expansion, generally older radiators were designed with bigger top tanks that were filled about half way.

Your carby may still be icing up, probably the idle compensation channel. Is it blowing black smoke as you attempt to move off?

Originally Posted by bee utey

Cut the overflow hose into the bottle with an angle cut, stop it sucking to the bottom of the bottle.

Check that the rad pressure cap has a small easy-to-lift button in the centre, this allows the coolant to be sucked back in. I have seen these gunk up and jam shut.

Your carby may still be icing up, probably the idle compensation channel. Is it blowing black smoke as you attempt to move off?

Thanks Bee Utey,
Just gave the overflow hose a snip. Now that i've done that, i'm not feeling very smart as I don't think the radiator cap does allow return. The 'button' is held down by a fairly stiff spring:




I haven't noticed black smoke, but I am usually more interested in trying to get moving than to see what's following
If it is icing up is there a way to prevent it? I don't have any more long trips in the Series planned so not sure when i'll get to test any theories

Actually your cap has a centre button, just lift the small brass dome thing in the middle of the cap lower face and clean all the gunk off. Also check the overflow hose isn't blocked with yuck, I see a lot of it in the photos of the cap. Time for a flush and new coolant?

The main way of preventing icing is to direct warm air into the carby, usually off the exhaust manifold area. Newer vehicles' carbies all have warm air feed in winter to stop icing up, usually controlled by a little thermostat spring thing on the air cleaner intake.

Gotcha Bee Utey, I learnt something new about radiator caps
Just emptied the radiator and stuck the hose in the bottom to back flush it, should get rid of some of the filth, this coolant had been sitting in the vehicle for a year prior to running so it's a little stale.


I suppose with the carby icing, just knowing when to expect it to happen and how to counter it retroactively is about the only way? I don't want to go changing things too much. I thought bolting straight onto the exhaust manifold would be enough!

problem a, wrong radiator cap, blocked recovery hose and possibly failing radaitor hoses.

problem B, possibly over heating of the fuel pump output line feeding vapour up to the carby. Try holding High idle when you come to a halt and see if that solve it, if it does the problems not icing.

Not related to LR's but I have found that water forcing passed the radiator cap AFTER the engine has been shutdown is (must be) caused by an increase in pressure. The only way that I can see, or have experienced, for the pressure to increase after the engine is switched off is for there to be a hot spot somewhere. Under normal conditions, with water circulating through the system, there is enough cooling for that hot-spot to not boil the water. When the engine is switched off, and the water around that hot-spot is no longer constantly being replaced, the coolant gets locally hot and boils, increasing the pressure and causing the radiator cap to lift.

I had an A-series engine that did exactly the same. It would run all day without a problem, but boiled the instant it was switched off. The water channels in the block were almost, but not quite, blocked around one cylinder. When the water was circulating there was just enough cooling to prevent boiling, but as soon as the water stopped flowing, it boiled. In that engine (and being careful not to get burnt!) you could put a stethoscope against the block and hear the bubbling....

doesnt just have to be a block gallery causing problems to give that effect, anything else that limits the flow of coolant at low engine speeds can do it.

Originally Posted by Blknight.aus

problem a, wrong radiator cap, blocked recovery hose and possibly failing radaitor hoses.

problem B, possibly over heating of the fuel pump output line feeding vapour up to the carby. Try holding High idle when you come to a halt and see if that solve it, if it does the problems not icing.

Agree with doesn't look like the right cap. As a comparison, a Toyota Crown I'm working on at the moment has a overflow/expansion tank. The radiator has a two way cap that allows overflow at a lower pressure than the expansion tanks cap (9 vs 13 psi by memory) and also allows return vacuum as the engine cools to let the fluid suck back into the system. This should be the difference between the cool/lower level and hot/higher levels in the expansion tank. The expansion tank cap allows fluid to expel if it's too full. Not sure if it allows suction of air back into the tank or not. Suspect it might as otherwise it may collapse the tank. And for a car from Toyota, in the 60's like this (triple SU's, fridge, auto dimming lights, a/c, power steer, 4 wheel discs, AM/FM/SW/8 track) it's unlikely they would allow that potential.