Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Smiths Round heater

And on to my next issue

I have the round Smiths Heater in the passenger footwell and although she gets a little warm, she doesn't get hot. The previous owner had a tap installed, so it must have got 'too warm' at some point in the past.

At the weekend I replaced the hoses, removed the tap and flushed the heater matrix in both directions. However she still doesn't seem to get warm.

I have one hose that goes from a 'take off' on the the water pump and into the heater matrix and a second hose that goes from the matrix to the inlet manifold.

When the engine runs, the hose from the heater matrix to manifold gets warm, whereas the hose from the water pump to heater remains cold. Personally I would have thought the opposite - the water should flow from the water pump, to the heater matrix and then back in through the manifold so the hoses should either be the same temperature, or the pump to matrix hose should be slightly warmer.

Any thoughts?

Both hoses are new. The matrix is clear and water is definitely flowing out of the water pump at pressure when running and the car maintains temperature well.

Manifold to heater then return to the water pump is the correct direction. It sounds like you have an air-lock. I'd loosen the clip on the heater return hose and gently pull it away when the engine's just started to see if any air comes out.

Ah, opposite to the way I thought and will explain why that hose gets hot first. Thank you.




I did this - got showered in fluid- there was definitely water coming out of the matrix. I'll have a crack again at the weekend and see if I can get any air out. Is there a preferred 'in and out' for the matrix? Currently the hose from manifold enters the matrix on the passenger left/passenger side and exits back to water pump on the right/drivers side.

If I was going to fit a tap, am I right to assume it should be in the hose going from manifold to matrix, rather than in the hose from matrix to pump (as fitted by Allon White).

Try removing both hoses and filling the heater manually

If you feed the hot supply in to the top of a matrix & the return cooler water out of the lower level, you will aid circulation by the thermo-syphonic effect

make sure a thermostat is fitted.

David Byrne

Unfortunately Inlet and Outlet are exactly the same level.

You could try eliminating the matrix by joining the two hoses together and seeing whether the whole length of the joined hose heats up. That should give you a better idea exactly where the problem is.

Good plan

Oh dear, not well designed, this makes you totally reliant on the efficiency of the water pump and the frictional losses of the hoses and matrix core, you may have a partial air lock in the heater - try a bit of a power flush with a hosepipe via the feed pipework