Click images to enlarge

XPAG Warming Up Times

This article can also be read in conjunction with :

XPAG Water Flow–Cooling.
Overheating or Vaporisation.
XPAG Overheating.
XPAG Engine Temperatures and Cooling.


Q, “Why does my modern car’s engine warm up faster and run smoother than my old MG?”


A, Your modern car’s engine has fuel injection controlled by an ‘ECU’. This item monitors the engine’s speed, air temperature, coolant temperature, level of oxygen left in the exhaust gasses, ignition advance required, engine load, electrical load and throttle position. It knows the engine is cold so it adjusts the engine’s fuel/air mixture to suit and automatically raises the engine’s idle RPM so it will not stall until it gets up to its normal running temperature. The cylinder block and head is probably thin-walled aluminium alloy and the cooling system probably holds up to half a gallon of water at the most. So the small amount of water heats up quickly and the alloy engine also takes little time to get up to its running temperature and soon warms up the water-heated inlet manifold. All this is taken care of out of your sight and hearing. You just turn the key to start it all off. A ballast resistor will power the 6 volt coil with 12 volts for a while to give a really fat spark at the plugs or something similar will be done with the electronic ignition. Once the resistor heats up, the feed will drop to 6 volts. The modern engine can also select a cool air intake or a hot air intake via its air filter.


Your solid cast-iron engine with its massive thick walls and the 8, 9, or 10 pints of coolant takes considerably longer to warm up. You have to adjust the choke to get the mixture ratio correct to start the cold engine and hope the choke’s little cam will also open the throttle a little if it is adjusted correctly. The starter motor will take nearly all the battery’s power and your 12 volt coil will have to cope with what is left. The colder the day the longer it will take to fire up. Once running it is up to you to adjust the choke. Most people push it in too soon and the engine will cough and spit back through the carburettor because the mixture is too weak. Then the engine stalls at the first few junctions because the tick-over is not fast enough. Others will leave the choke out too long and wash all the oil from the cylinder walls increasing cylinder wear. On cold, damp mornings the unheated carburettor can get encased in ice due to the venturi effect of the choke, this make vaporising the fuel almost impossible. (Air passing through a narrow gap will speed up and also cool down.) So you get lumps of neat petrol going through the engine unburnt. That is why you can smell an older car when its choke is in use. The XPAG can only draw cold air. After quite a few miles the engine will eventually get to its running temperature and you will have used considerably more fuel than the modern car above.


So when your modern car gets a coolant leak, it has virtually no reserve, so you quickly blow the head gasket. This means having it re-skimmed as it may well have warped with the excess heat. Many, many Rover ‘K Series’ engines have suffered this fate. The thing to do is to always monitor your modern engine’s temperature!


Article by Neil Cairns