From a point at sea, to the circles of your mind, this is Dave
Wheatley:

Tonight while running on lpg sat in traffic my RR started misfiring on &
off then seemed ok. Then traffic moved and as I tried to move off it
started spluttering, almost stalling. I quickly flicked over to petrol &
it was fine. A few more 'tests' on the journey proved that it is only on
gas that it happens. I'm having to top up the rad with coolant as the
dash light keeps coming on - I've pinpointed that to the expansion tank
cap- I can hear it escaping when hot, so I'll get one of those in the
next few days. The engine isnt overheating but I wondered if the two
things could be related seeing as the pipework flows through the gas
assembly. I know the gas level indicators are usually a way out but I'm
easily 60/70 miles from being empty (I use the trip meter to guage it)
There are no obvious faults (hanging wires etc)

The vapouriser takes heat from the cooling system to stop it from
freezing as the gas turns to liquid (latent heat of vapourisation and
all that). If the water level drops to the point where none is getting
to the vapouriser then it will start to ice up. The effect is similar
to carb. icing, which some petrol engines used to be prone to.

I guess at low engine speeds, when stuck in traffic, the coolant is
not circulating very fast, which may exacerbate the low level.

If it happens again, switch to petrol for a few minutes to give the
vapouriser time to thaw out, then see if it is still doing it.

Also, I'm a little concerned by your exapnsion cap theory. The cooling
system will be pressurised, but the cap is meant to allow air out
above a certain pressure (and back in again if the pressure drops too
low as it cools). However, if you are not filling the water level
higher than the maximum level mark, and it is still chucking it out,
then something is amiss (on my car I can remove the cap altogether and
not lose any coolant). Try a new cap by all means, but it may be
something more than this. I'd be happy to hear I'm talking bollox
here.


--

Stewart Hargrave

A lot faster than public transport


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