I recently noticed that a neighbour had changed his car, but not for the better. The car he had bought was older and shabbier looking than his previous wheels.
When I asked the reason for the swap, he told me that although his car would start easily on cold mornings, after being driven for anything more than 15km or so in the recent spell of hot weather, and then switching off, it was impossible to restart. After the latest hot start failure, he had lost his cool and got rid of it.
OK, I know how annoyed he must have been, but nevertheless he made a foolish move.
We all get peeved whenever an engine refuses to start, whether in ultracold conditions because of a tired battery and thickening oil when a cold engine is reluctant to spin, or in hot conditions when the under-bonnet temperature can exceed 120°C.
(VERY) COLD STARTS
I remember that during English winters we poured boiling water over engines to help get them started. Some people used electric heater blowers to give the engine a warm-up on cold mornings. Some even placed electric fires under the sump, but definitely not a recommended practice!
On any engine with a carburettor, very hot conditions might boil the petrol in the fuel bowl, losing it in vapour form. The delay in starting occurs because the bowl takes time to refill and reach the discharge nozzle.
But, carburettors aside, all engines can suffer from vaporised fuel in the fuel lines (vapour lock) which, because vapour is less compressible, the fuel pump is not always able to deliver fresh fuel.
HEAT SOAK
Fuel injection is superior to carburetion in many ways, but the number of fuel lines to the various injectors – some near the hot parts of the engine – increases the likelihood of heat soak.
Some systems add a little extra fuel, similar to that used in cold start systems, to combat vaporisation. During slow cranking, this aids starting and then with the engine running, increased air and fuel flow get rid of vapour lock.
Warm starting is another story entirely because a warm, as opposed to a cold engine, helps vaporise the fuel. As in normal warm running, the demands are simple and fuel is unlikely to condense on to warm parts of the engine.
Starting techniques vary from driver to driver and we all get to know the best way for our own vehicles.
Some cars with carburettors start easier with a slight dab of the accelerator, thus making the accelerator pump send a little extra fuel. Some people pump the throttle aggressively, but if that works for you, it’s OK.
If a fuel-injection system senses that the temperature is slightly below normal, it might improve warm starts by sending a slightly richer mixture and increasing, again slightly, intake air flow.
It’s nice to have these modern management systems doing the thinking for us, rather than getting the non-starter pushed and towed down the road as we often had to in the old days.
All the same, the basic reasons for reluctant starting and poor running are still often caused by no more than duff spark plugs and dirty filters. - Star Motoring