Hesitation

[Clifford Pope]

Originally Posted by classicswede

The vapouriser should be T'ed into both of the heater hoses. If it is plumbed in correctly I would suspect some kind of blockage or a nearly dead water pump. If it is plumbed in correctly then first step would be to disconect one of the water hoses and run a hose pipe through the vapouriser. leaving one pipe connected will flush the full line.

I've done all that. I had the pump off recently to replace the rubber seal, so I know it is good.

I suspect that the clue is in the "T'ed into both the heater hoses". It is a T junction, but the vapouriser is connected to the side limb, and the heater is straight through. I don't know what sort of heat exchange matrix there is inside the vapouriser, but experiment shows that water resistance through the heater is much less, with straight through connection, than through the vapouriser.

So on cold mornings I now have the routine:
1) start on petrol and only switch over to gas when the temperature needle is climbing steadily past the 1/4 position (half mile)
2) open the heater valve a small amount when the gauge is up to 1/2, ie Normal
3) open the heater valve fully, if required, only after about 5 miles when the engine block is fully hot.

Opening the heater valve fully, prematurely, can sap all the heat in that circuit, even if the engine is apparently up to temperature.

Perhaps strictly speaking Y- junctions would be better than Ts. With a T junction there is not even a certainty that water will flow in the required direction. A rapid flow through a T junction can even draw fluid IN rather than pump it OUT - that is the principle of laboratory vacuum pumps that connect to a water tap.

Anyway, I can live it now I have found a theory that appears to explain what is going on.

[classicswede]

Y's are better and I do keep some in stock but often you can not use them. Normaly the issue is not enough heat getting to the heater on most cars.

With the 240 the best way of fitting the T'es is where the pipes bend going to the bulkead. I cut the bend out and then use teh T to form the bend and give the spur off for the vapouriser. Going it that gives an unrestricted path to the vapouriser, not that the normal method of tapping in is a problem in most cases.